International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp9010011
Authors: Stéphane Moreau Michel Roger
The present paper is aimed at providing an updated review of prediction methods for the aerodynamic noise of ducted rotor–stator stages. Indeed, ducted rotating-blade technologies are in continuous evolution and are increasingly used for aeronautical propulsion units, power generation and air conditioning systems. Different needs are faced from the early design stage to the final definition of a machine. Fast-running, approximate analytical approaches and high-fidelity numerical simulations are considered the best-suited tools for each, respectively. Recent advances are discussed, with emphasis on their pros and cons.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp9010010
Authors: Alexandra P. Schneider Benoit Paoletti Xavier Ottavy Christoph Brandstetter
Experimental monitoring of blade vibration in turbomachinery is typically based on blade-mounted strain gauges. Their signals are used to derive vibration amplitudes which are compared to modal scope limits, including a safety factor. According to industrial guidelines, this factor is chosen conservatively to ensure safe operation of the machine. Within the experimental campaign with the open-test-case composite fan ECL5/CATANA, which is representative for modern lightweight Ultra High Bypass Ratio (UHBR) architectures, measurements close to the stability limit have been conducted. Investigation of phenomena like non-synchronous vibrations (NSV) and rotating stall require a close approach to the stability limit and hence demand for accurate (real-time) quantification of vibration amplitudes to ensure secure operation without exhaustive safety margins. Historically, short-time Fourier transforms of vibration sensors are used, but the complex nature of the mentioned coupled phenomena has an influence on amplitude accuracy, depending on evaluation parameters, as presented in a previous study using fast-response wall-pressure transducers. The present study investigates the sensitivity of blade vibration data to evaluation parameters for different spectral analysis methods and provides guidelines for fast and robust surveillance of critical vibration modes.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp9010009
Authors: Nicola Casari Ettore Fadiga Stefano Oliani Mattia Piovan Michele Pinelli Alessio Suman
Automotive fans, small wind turbines, and manned and unmanned aerial vehicles (MAVs/UAVs) are just a few examples in which noise generated by the flow’s interaction with aerodynamic surfaces is a major concern. The current work shows the potential of a new airfoil shape to minimize noise generation, maintaining a high lift-to-drag ratio in a prescribed Reynolds regime. This investigation uses a multifidelity approach: a low-fidelity semiempirical model is exploited to evaluate the sound pressure level (SPL). Fast evaluation of a low-cost function enables the computation of a large range of possible profiles, and accuracy is added to the low-fidelity response surface with high-fidelity CFD data. The constraint of maintaining a predefined range of the lift coefficient and lift-to-drag ratio ensures the possibility of using this profile in usual design procedures.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp9010008
Authors: Christian Lehr Pascal Munsch Romuald Skoda Andreas Brümmer
The acoustic properties of a single-stage centrifugal pump with low specific speed are investigated by means of compressible 3D CFD simulations (URANS) and experiments. In order to determine the pump’s acoustic transmission and excitation characteristics, a four-pole approach in the frequency domain is used. The transmission parameters determined by simulation are compared to experiments in water and air as functions of the Helmholtz number. The results indicate that the acoustic transmission characteristics within the experiments are significantly influenced by the structural compliance of the volute casing in terms of a fluid–structure interaction (FSI). A modelling approach for a one-dimensional representation of the centrifugal pump’s acoustic transmission characteristics in the time and frequency domains is applied to the current pump. As one model parameter, the effective speed of sound in the 1D model needs to be reduced to 607 ms−1 to account for the FSI. The agreement of the simulation results and the experiments underlines the above statement about the influence of the FSI. In a last step, the acoustic excitation parameter, depicted as monopole and dipole amplitudes, at two different blade-passing frequencies (fBP≈[111;169] Hz) are determined for several operating points. Especially for dipole amplitudes, a good agreement between experiments and simulations can be seen. The monopole amplitudes are also of similar orders of magnitude, but show stronger deviations. The cause of discrepancies between the 3D CFD simulations and experiments is believed to be the neglected influence of the FSI and surface roughness as well as the inaccurate reproduction of flow separation at the volute’s tongue due to the use of wall functions. A final important observation made during the numerical investigations is that the excitation mechanisms at the blade-passing frequency are probably independent of the piping system’s acoustic impedance.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp9010007
Authors: Sanjay Nambiar Anan Ashrabi Ananno Herman Titus Anton Wiberg Mehdi Tarkian
In the quest to enhance the efficiency of gas turbines, there is a growing demand for innovative solutions to optimize high-pressure turbine blade cooling. However, the traditional methods for achieving this optimization are known for their complexity and time-consuming nature. We present an automation framework to streamline the design, meshing, and structural analysis of cooling channels, achieving design automation at both the morphological and topological levels. This framework offers a comprehensive approach for evaluating turbine blade lifetime and enabling multidisciplinary design analyses, emphasizing flexibility in turbine cooling design through high-level CAD templates and knowledge-based engineering. The streamlined automation process, supported by a knowledge base, ensures continuity in both the mesh and structural simulation automations, contributing significantly to advancements in gas turbine technology.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp9010006
Authors: Michael van de Noort Peter T. Ireland
Double-Wall Effusion Cooling schemes present an opportunity for aeroengine designers to achieve high overall cooling effectiveness and convective cooling efficiency in High-Pressure Turbine blades with reduced coolant usage compared to conventional cooling technologies. This is accomplished by combining impingement, pin-fin and effusion cooling. Optimising these cooling schemes is crucial to ensuring that cooling is achieved sufficiently at high-heat-flux regions and not overused at low-heat-flux ones. Due to the high number of design variables employed in these systems, optimisation through the use of Computational Fluid Dynamics (CFD) simulations can be a computationally costly and time-consuming process. This study makes use of a Low-Order Flow Network Model (LOM), developed, validated and presented previously, which quickly assesses the pressure, temperature, mass flow and heat flow distributions through a Double-Wall Effusion Cooling scheme. Results generated by the LOM are used to rapidly produce an ideal cooling system design through the use of an Evolutionary Genetic Algorithm (GA) optimisation process. The objective is to minimise the coolant mass flow whilst maintaining acceptable metal cooling effectiveness around the external surface of the blade and ensuring that the Backflow Margin for all film holes is above a selected threshold. For comparison, a Genetic Aggregation model-based optimisation using CFD simulations in ANSYS Workbench is also conducted. Results for both the reduction of coolant mass flow and the total optimisation runtime are analysed alongside those from the LOM, demonstrating the benefit of rapid low-order solving techniques.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp9010005
Authors: Abdelrahman S. Abdeldayem Salma I. Salah Omar A. Aqel Martin T. White Abdulnaser I. Sayma
Supercritical carbon dioxide (sCO2) can be mixed with dopants such as titanium tetrachloride (TiCl4), hexafluoro-benzene (C6F6), and sulphur dioxide (SO2) to raise the critical temperature of the working fluid, allowing it to condense at ambient temperatures in dry solar field locations. The resulting transcritical power cycles have lower compression work and higher thermal efficiency. This paper presents the aerodynamic flow path design of a utility-scale axial turbine operating with an 80–20% molar mix of CO2 and SO2. The preliminary design is obtained using a mean line turbine design method based on the Aungier loss model, which considers both mechanical and rotor dynamic criteria. Furthermore, steady-state 3D computational fluid dynamic (CFD) simulations are set up using the k-ω SST turbulence model, and blade shape optimisation is carried out to improve the preliminary design while maintaining acceptable stress levels. It was found that increasing the number of stages from 4 to 14 increased the total-to-total efficiency by 6.3% due to the higher blade aspect ratio, which reduced the influence of secondary flow losses, as well as the smaller tip diameter, which minimised the tip clearance losses. The final turbine design had a total-to-total efficiency of 92.9%, as predicted by the CFD results, with a maximum stress of less than 260 MPa and a mass flow rate within 1% of the intended cycle’s mass flow rate. Optimum aerodynamic performance was achieved with a 14-stage design where the hub radius and the flow path length are 310 mm and 1800 mm, respectively. Off-design analysis showed that the turbine could operate down to 88% of the design reduced mass flow rate with a total-to-total efficiency of 80%.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp9010004
Authors: Andrea Notaristefano Giacomo Persico Paolo Gaetani
Turbulence intensity impacts the performance of turbine stages and it is an important inlet boundary condition for CFD computations; the knowledge of its value at the turbine inlet is then of paramount importance. In combustor–turbine interaction experimental studies, combustor simulators replace real combustors and allow for the introduction of flow perturbation at the turbine inlet. Therefore, the turbulence intensity of a combustor simulator used in a wide experimental campaign at Politecnico di Milano is characterized using a hot-wire probe in a blow-down wind tunnel, and the results are compared to URANS CFD computations. This combustor simulator can generate a combination of a swirl profile with a steady/unsteady temperature disturbance. In the cold unsteady disturbance case, hot-wire measurements are phase-averaged at the frequency of the injected perturbation. The combustor simulator turbulence intensity is measured at two different axial positions to understand its evolution.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp9010003
Authors: Matteo Dellacasagrande Davide Lengani Daniele Simoni Marina Ubaldi
The bursting phenomenon consists in the switch of a laminar separation bubble from a short to a long configuration. In the former case, reduced effects on profile pressure distribution are typically observed with respect to the attached condition. On the contrary, long bubbles provoke significant variations in the loading coefficient upstream of the separation position, with increased risk of stall of the lifting surfaces. The present work presents an experimental database describing separated boundary layers evolving under different Reynolds numbers, adverse pressure gradients and free-stream turbulence levels. Overall, more than 80 flow conditions were tested concerning short and long bubbles for the characterization of separated flows under turbine-like conditions. Measurements were performed on a flat plate geometry using a fast-response Particle Image Velocimetry (PIV) system. For each flow case, two sets of 6000 flow records were acquired with an acquisition frequency equal to 300 and 1000 Hz. Based on existing criteria for the identification of the bursting phenomenon, the flow cases were clustered in terms of short and long bubble states. Additionally, the kind of instability (i.e., convective or absolute) developing into the separated boundary layer was identified based on flow statistics. The present data captures the existing link between the bursting of a laminar separation bubble and the onset of the absolute instability of the separated shear layer, with stationary vortices forming in the dead air region.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp9010002
Authors: Bao Liu Maarten Vanierschot Frank Buysschaert
The present work examines the capabilities of two transition models implemented in ANSYS Fluent in the open-water performance prediction of a rim-driven thruster (RDT). The adopted models are the three-equation k−kL−ω and the four-equation γ−Reθ models. Both of them are firstly tested on a ducted propeller. The numerical results are compared with available experimental data, and a good correlation is found for both models. The simulations employing two transition models are then carried out on a four-bladed rim-driven thruster model and the results are compared with the SST k−ω turbulence model. It is observed that the streamline patterns on the blade surface are significantly different between the transition and fully turbulent models. The transition models can reveal the laminar region on the blade while the fully turbulent model assumes the boundary layer is entirely turbulent, resulting in a considerable difference in torque prediction. It is noted that unlike the fully turbulent model, the transition models are quite sensitive to the free-stream turbulence quantities such as turbulent intensity and turbulent viscosity ratio, as these quantities determine the onset of the transition process. The open-water performance of the studied RDT and resolved flow field are also presented and discussed.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp9010001
Authors: Alexander Hergt Tobias Danninger Joachim Klinner Sebastian Grund Manfred Beversdorff Christian Werner-Spatz
In this paper, an experimental and numerical investigation of the effect of leading-edge erosion in transonic blades was performed. The measurements were carried out on a linear blade cascade in the Transonic Cascade Wind Tunnel of DLR in Cologne at two operating points with an inflow Mach number of 1.05 and 1.12. The numerical simulations were performed by ANSYS Germany. The type and specifications of the erosion for the study were derived from real engine blades and applied to the leading edges of the experimental cascade blades using a waterjet process, as well as modeled in detail and meshed within the numerical setup. Numerical simulations and extensive wake measurements were carried out on the cascades to evaluate the aerodynamic performance. The increase in losses was quantified to be 4 percent, and a reduction in deflection and a rise in pressure were detected at both operating points.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040055
Authors: Christian Windemuth Martin Lange Ronald Mailach
A growing significance of flexible steam turbine operation challenges the control of turbines, as part load operation using control valves can be accompanied by highly unsteady flow conditions. The increased dynamic load induced by pressure forces can reduce the reliable operating range, weaken the valve, and lead to mechanical failures. The geometry of the valve plays a major role in the reduction of dynamic forces. Using a scaled control valve, experiments were conducted with a focus on the dynamic behavior of the valve head. A spherical valve shape favoring unstable operation was used as a reference case, and the desired instability was proven by measurements. Different modified valve geometries based on literature featuring separation edges were then tested against the spherical shape. Results indicate the improved stability of the modified geometries over the reference geometry. For most of the operating range, vibrations were drastically reduced, and the overall flow stabilized.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040054
Authors: Claudio Bernardi Federico Porcacchia Claudio Testa Pietro De Palma Stefano Leonardi Stefania Cherubini
This paper deals with large onshore wind turbine aeroacoustics. Noise from the NREL 5 MW device is predicted by the permeable-surface Ffowcs Williams–Hawkings equation (FWH-P), starting from the postprocessing of LES data on different acoustic surfaces S. Their size and placement is aimed at embedding most of the aerodynamic sources of sound surrounding rotor and nacelle. Due to the presence of eddies that inevitably cross S, this paper compares results from open and closed acoustic surfaces, and the outflow disk averaging technique. The issues related to the interpolation process of LES data on S is discussed as well. In order to assess the LES/FWH-P aeroacoustic platform, LES and FWH-P pressures are compared in the very-near field. It is shown that, within the limits of the discretization settings imposed by the interpolation procedure and for the Reynolds number working condition investigated herein, the lack of quadrupole sources outside the permeable surface(s) deeply affect the quality of FWH-P acoustic pressures with respect to direct LES signals.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040053
Authors: Oliver Sjögren Tomas Grönstedt Anders Lundbladh Carlos Xisto
In modern turbofan engines, the bypass section of the fan stage alone provides the majority of the total thrust required in cruise, and the size of the fan has a considerable effect on the overall engine weight and nacelle drag. Thrust requirements in different parts of the flight envelope must also be satisfied together with sufficient margins towards stalling. An accurate description of the interdependencies between the relevant performance and design attributes of the fan stage alone—such as efficiency, surge margin, fan-face Mach number, stage loading, flow coefficient, and aspect ratio—are therefore necessary to estimate system-level objectives such as mission fuel burn and the direct operating cost with enough confidence during the conceptual design phase. The contribution of this study is to apply a parametric optimization approach to the conceptual design of fan stages for low specific thrust turbofans based on the streamline curvature method. Trade-offs between fan stage attributes for Pareto-optimal solutions are modeled by training Kriging surrogate models on the results from the parametric optimization. A case study is provided in the end to demonstrate the potential implications of including a higher level of fan-stage parameter interdependency in an engine systems model. Results implied that being able to predict the rotor solidity required to maintain a given average blade loading—in addition to stage efficiency—is of significant importance when it comes to evaluating the trade-off between engine weight and thrust-specific fuel consumption.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040052
Authors: Marco Castaldi Ignacio Mayo Jacques Demolis Frank Eulitz
Helicopter and turboprop engines are susceptible to the ingestion of debris and other foreign objects, especially during take-off, landing, and hover. To avoid deleterious effects, filters such as Inlet Particle Separators (IPS) can be installed. However, the performance and limitations of these systems have to be investigated before the actual equipment can be installed in the aircraft powerplant. In this paper, we propose different numerical methods with increasing resolution in order to provide an aerodynamic characterization of the IPS, i.e., from a simple semi-empirical model to 3D large eddy simulation. We validate these numerical tools that could aid IPS design using experimental data in terms of global parameters such as separation efficiency and pressure losses. For each of those tools, we underline weaknesses and potential benefits in industry practices. Unsteady flow analysis reveals that detached eddy simulation is the trade-off choice that allows designers to most effectively plan experimental campaigns and mitigate risks.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040051
Authors: Leander Hake Stephan Sundermeier Stefan aus der Wiesche
The results of profile loss measurements, including trailing edge flow details, are presented for the flow of an organic vapor through a linear turbine cascade. The so-called VKI-I blade profile from the open literature was chosen for the cascade, and the working fluid was NOVEC 649. Pitot probes and hot-wire anemometry were employed to measure the flow field up and downstream of the cascade. Details of the unsteady flow caused by the trailing edge of the blades and the turbulent spectrum were investigated using hot-wire anemometry. The new organic vapor flow results were compared with the literature data obtained for air and with the prediction of conventional literature loss models. It was found that, under certain thermodynamic conditions, specific traditional loss models can reasonably predict organic Rankine cycle (ORC) turbines’ profile loss. Still, significant deviations between the loss models and the experimental data can also occur.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040050
Authors: Benjamin J. Brimacombe James A. Scobie Joseph M. Flynn Carl M. Sangan Oliver J. Pountney
This paper presents experimental measurements of adiabatic effectiveness for three transpiration cooling porosities (ϕ= 0.3, 0.4, and 0.5) constructed from gyroid lattice structures. To the authors’ knowledge, this is the first use of a Triply Periodic Minimal Surface (TPMS) function to produce transpiration test coupons of varying porosity. Polymer gyroid lattice structures were successfully printed using Stereolithography (SLA) down to ϕ= 0.3 for a print resolution of 25 microns and unit cell size of 2 mm. Cooling performance was measured in a small-scale wind tunnel. High-resolution Infrared Thermography was used to determine wall temperatures downstream of the porous section. When tested at both common blowing ratios (M = 0.029, 0.048, and 0.062) and common injection ratios (F = 0.010, 0.017, and 0.022) the cooling performance was found to be dependent on porosity for constant M but not for constant F. Having determined F as the more important parameter for comparison, results are presented alongside transpiration and effusion data from literature.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040049
Authors: Simon Pramstrahler Andreas Peters Mikel Lucas García De Albéniz Peter Adrian Leitl Franz Heitmeir Andreas Marn
A turbine vane frame is a special type of intermediate turbine duct, and is one option to improve the efficiency and reduce the length and weight of an aero-engine. However, due to its geometry, it features a complex flow field, and therefore in-depth aerodynamic investigations are necessary. Especially for aviation, every component needs to function reliably during all operating points. To perform this study at the Institute for Thermal Turbomachinery at the Graz University of Technology, the Subsonic Test Turbine Facility for Aerodynamic, Aeroacoustic and Aeroelastic Investigations was equipped with a turbine vane frame and a low-pressure turbine located downstream. Measurements were taken with aerodynamic five-hole probes for three operating points, and were compared with steady-state and transient simulations as well as analytic solutions for the pressure drop in the TVF. Finally, the most important loss mechanisms are described.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040048
Authors: Tobias Haeckel Dominik Paul Sebastian Leichtfuß Heinz-Peter Schiffer Werner Eißler
The surge limit of centrifugal compressors is a key parameter in the design process of modern turbochargers. Numerical methods like steady-state simulations are state-of-the-art methods for predicting the performance of the centrifugal compressor. In contrast to that, the determination of the surge limit with any numerical method is still an unsolved challenge. Since the extensive work of Greitzer and many other researchers in this field, it is well-known that surge is a system-dependent phenomenon. In the case of steady-state simulations, the simulation domain is chosen to be as small as possible due to the numerical cost. This simply implies that there is no system information included in the numerical model. Therefore, it is not possible to determine any system-dependent surge limit with today’s applied numerical methods. To overcome this issue, an enhanced Greitzer surge model, which has been developed at Tu Darmstadt, should act as a link between the simulation and the system in which the compressor will be operated. The focus of this paper will rather be on the methodology of determining the surge limit by means of numerical data than on the surge model itself. The methodology will be validated by experimental data of different systems.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040047
Authors: Edwin Joseph Munoz Lopez Alexander Hergt Till Ockenfels Sebastian Grund Volker Gümmer
The successful design of compressor blades through numerical optimization relies on accurate CFD-RANS solvers that are able to capture the general performance of a given design candidate. However, this is a difficult task to achieve in transonic flow conditions, where the flow is dominated by inherently unsteady shock effects. In order to assess the current gap between numerics and experiments, the DLR has tested the recently optimized Transonic Cascade TEAMAero at the transonic cascade wind tunnel. The tests were performed at a Mach number of 1.2 and with inflow angles between 145 and 147°. The results indicate satisfactory agreement across the expected working range, over which the cascade losses were consistently predicted within a 3–6% error. However, some key differences are observed in the details of the wake and in the performance near the endpoints of the working range. This comparison helps validate the design process but also informs its constraints based on the limitations of CFD-RANS solvers.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040046
Authors: Qiaorui Si Fanjie Deng Yu Lu Minquan Liao Shouqi Yuan
A numerical method using combined detached-eddy simulation (DES) and a cavitation model considering the rotation effect is used for unsteady cavitation flow field of the centrifugal pump. A closed-type pump test system was established to obtain the pump performance and pressure pulsation characteristics under different flow rates and cavitation condition, which provide boundary conditions and verification of calculations. Based on the calculation results of the unsteady flow field of the centrifugal pump cavitation, the entropy generation analysis of the flow field and an analysis of the pressure fluctuation characteristics were carried out. Then, we tried to reveal the relationship between cavitation and the deterioration of the centrifugal pump performance and the generation of the unstable operation excitation force. The internal energy loss is mainly concentrated in the impeller, volute, and pump cavity area, which accounts for more than 85% of the total entropy generation. The characteristic frequency of a Strouhal number of about 0.333 appears at the volute tongue due to the cavitation flow spread downstream.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040045
Authors: Robin M. Robrecht Peter F. Pelz
Grooved liquid annular seals have a significant influence on the design of turbomachines. Corresponding lubrication film models need to account for the different friction behavior of the grooves compared to plain seals. However, there is a lack of reliable and validated models for this purpose. Thus, the applicability of a friction factor model is explored and a calibration method is presented. A single square groove is investigated by means of 96 steady-state RANS simulations for different operation conditions and groove geometries. The results are used to calibrate the friction model and successfully verify it in terms of the pressure drop over the groove. For validation, two full grooved seals with relatively large square grooves were investigated by experiment. The friction model was incorporated in a lubrication model and compared to the measurement data for the pressure difference and the resulting force for specified leakage and eccentricity. The model predictions for the pressure difference can be considered very good. The force predictions show significant deviation, but can be considered acceptable given the low force magnitudes and measurement uncertainty. The results offer a general validity to our friction model approach, assumptions and the calibration method.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040044
Authors: Riccardo Toracchio Fabrizio Fontaneto Koen Hillewaert
This paper presents the numerical characterization of a highly loaded compressor by means of 3D unsteady RANS simulations. The focus is on critical flow structures and their evolution at different operating points of the machine. First, the numerical setup and mesh quality are presented to support the reliability of the provided results. The comparison against experiments is then described for this purpose. Later, a full description of the unsteady behavior of the machine is provided, giving special attention to the two regions where the most critical features are expected: the rotor hub wall and the casing. Rotor–stator interactions are then investigated and the role of the inlet guide vane (IGV) is finally discussed. Results are analyzed at design and near-stall conditions, with a focus on the behavior close to the stability limit at 100% speed.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040043
Authors: Filippo De Girolamo Lorenzo Tieghi Giovanni Delibra Valerio Francesco Barnabei Alessandro Corsini
Wind turbines play a major role in the European Green Deal for clean energy transition. Noise is a critical aspect among open technological issues, as it determines the possibility of onshore installations near inhabited places and the possible detrimental effects on wildlife when offshore. This paper assesses the accuracy of different approaches to predicting the sound pressure level (SPL) of a wind turbine. The 2.75 MW Neg Micon NM80 horizontal axis wind turbine (HWAT) was simulated in OpenFOAM, modeling the turbine with the actuator line method (ALM) implemented in the turbinesFoam library. Two different inflow conditions were considered: a stationary inflow with a typical atmospheric boundary layer profile and a time-dependent inflow derived from a precursor channel with fully turbulent conditions. The surrogate model for noise prediction used for this work is based on the synthetic/surrogate acoustics models (SAMs) of Amiet and Brooks-Pope-Marcolini (BPM). This approach allows for blade motion modeling and the prediction of the SPL of the URANS postprocessing results. The SPL spectrum obtained was then compared to the results from the other aeroacoustic solvers of IEA Task 39 participants, showing the best performance in the fully turbulent case. The results demonstrate that coupling between the ALM and surrogate acoustics provides more accurate results than the blade element momentum (BEM) approach.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040042
Authors: Michael Mansour Dominique Thévenin
This paper aims to summarize the results of several experimental investigations regarding two-phase liquid–gas flows in radial centrifugal pumps. The main objective is to combine the corresponding experimental results and collect the obtained knowledge to provide a better understanding of this configuration. The simultaneous transport of the two phases, the phase segregation, and the regions of safe or critical pump performance were described for a wide variety of pump configurations. This review covers single- and two-phase pumping conditions, performance degradation, pump breakdown, performance hysteresis, different flow regimes, flow regime maps, flow instabilities, and surging. This manuscript also considers the influence of employing different pump configurations on pump performance and flow regimes. This includes comparisons between closed and semi-open impellers, standard and increased tip clearance gaps, and running the pump with and without an inducer. Many of the results discussed have been published in a series of research papers. They were all collected, summarized, and compared systematically in the present review.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040041
Authors: Romain Hottois Arnaud Châtel Tom Verstraete
Numerical optimization methods are widely used for designing turbomachinery components due to the cost and time savings they can provide. In the available literature, the shape optimization of radial compressors mainly focuses on improving the impeller alone. However, it is well-established knowledge that the volute plays a key role in the overall performance of the compressor. The aim of the present paper is to perform an adjoint-based optimization of a volute that is designed for the SRV2-O compressor. The CAD model was first created by using the parametrization of 33 design parameters. Then, a butterfly topology was applied to mesh the computational domain with a multi-block structured grid, and an elliptic smoothing procedure was used to improve the quality of the fluid grid. A steady-state RANS CFD solver with a Spalart-Allmaras turbulence model was used to solve the Navier–Stokes equations, and then the flow sensitivities were computed with an adjoint solver. The objective function consists of minimizing the loss coefficient of the volute. The optimization is performed to obtain an improved design with a 14% loss reduction. A detailed flow and design analysis is carried out to highlight the loss reduction mechanisms, followed by the optimizer. Finally, the compressor map of the full stage is compared between the baseline and the optimized volute from the CFD simulations using a mixing plane interface. This research demonstrates the successful use of a gradient-based optimization technique to improve the volute of a radial compressor and opens the door towards simultaneously optimizing the wheel and the volute.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040040
Authors: Manuel Ernesto Maqueo Martínez Stefan Schippling Markus Schatz Damian M. Vogt
Considerable progress has been achieved in recent decades in understanding the phenomena related to the onset of condensation in steam flows, both experimentally and especially numerically. Nevertheless, there is still a certain disagreement between the different numerical models used. Unfortunately, the available experimental validation data are not sufficiently detailed to allow for proper validation of computational fluid dynamics (CFD) simulations. Therefore, this paper presents new experimental data for condensing steam flows, acquired in a supersonic nozzle according to Barschdorff, at the Institute of Thermal Turbomachinery Laboratory (ITSM) at the University of Stuttgart. A steady inlet pressure of approximately 784 mbar was set for three inlet temperatures down to 100.2 ∘C. Condensation onset is accurately captured across the nozzle, using down to 1 mm spatial resolution for both pneumatic and light spectra measurements. CFD simulations were performed using the commercial solver ANSYS CFX. The droplet diameters are numerically overestimated by approximately a factor of 1.5. Disagreement has been found between original Barschdorff’s experiments and measurements at ITSM. However, there is a good agreement in terms of the pressure distribution along the nozzle axis between experimental and numerical results. The reproducibility of the results is excellent.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040039
Authors: Hanbing Ma Oliver Kirschner Stefan Riedelbauch
The head and flow rate of a pump characterize the pump performance, which help determine whether maintenance is needed. In the proposed method, instead of a traditional flowmeter and manometer, the operating points are identified using data collected from accelerometers and microphones. The dataset is created from a test rig consisting of a standard centrifugal water pump and measurement system. After implementing preprocessing techniques and Convolutional Neural Networks (CNNs), the trained models are obtained and evaluated. The influence of the sensor location and the performance of different signals or signal combinations are investigated. The proposed method achieves a mean relative error of 7.23% for flow rate and 2.37% for head with the best model. By employing two data augmentation techniques, performance is further improved, resulting in a mean relative error of 3.55% for flow rate and 1.35% for head with the sliding window technique.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040038
Authors: Katharina Brinkmann Thomas Hoffmann Lars Panning-von Scheidt Heinrich Stüer
In this work, the vibration response of an academic free-standing turbine blisk is analyzed in regard to transient resonance passages. Measurement data are recorded using strain gauges and tip timing to evaluate the blades first bending mode both linearly and with two different types of underplatform dampers. These results are validated against steady-state responses and show good agreement with each other. To examine the effects of a transient resonance passage, response functions of each blade are evaluated both with and without the underplatform dampers. It is shown that friction damping is able to inhibit any appearance of a transient ring-down. Additionally, a multi-mass oscillator model with frictional contacts is analyzed, which qualitatively exhibits the same dynamics as the measurements. Due to geometric mistuning, all blades exhibit different vibration responses. This can lead to a transient amplitude amplification, which is observed on several blades. Analogously, this phenomenon can be mitigated by friction damping.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040037
Authors: Takashi Ando
For engines operating using heavy fuel oil (HFO), the nozzle rings of turbocharger turbines are prone to severe degradation because of contamination with unburned fuel deposits. This contamination may lead to increased excitation of blade resonance. A previous study provides technical guidelines on how to extract the relevant information from pulsation spectra using a single probe installed away from the turbine trailing edge and some sound experimental proofs of integral mode turbine vibration detection. These theoretical discussions only allude to the effects of mistuning and interferences due to classical blade passing frequencies on sound radiation patterns emitted by integral blade vibration modes. In this study, both effects are thoroughly discussed. Combining the knowledge of theoretical study and further experimental results, the application range of this blade vibration detection method can be remarkably extended.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8040036
Authors: Gustavo Lopes Loris Simonassi Sergio Lavagnoli
The aerodynamics of a high-speed low-pressure turbine (LPT) cascade were investigated under steady and unsteady inlet flows. The tests were performed at outlet Mach (M) and Reynolds numbers (Re) of 0.90 and 70k, respectively. Unsteady wakes were simulated by means of a wake generator equipped with bars. A bar reduced frequency (f+) of ∼0.95 was used for the unsteady case. The inlet flow field was characterized in terms of the total pressure profile and incidence. The blade aerodynamics at midspan and the secondary flow region were investigated by means of pneumatic taps and hot-film sensors. The latter provided a novel view into the impact of the secondary flows on the heat transfer topology on the blade suction side (SS). The cascade performance was quantified in terms of the outlet flow angle and losses by means of a directional multi-hole probe. The results report the phase-averaged impact of unsteady wakes on the secondary flow structures in an open test case high-speed LPT geometry.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030035
Authors: Loris Simonassi Gustavo Lopes Sergio Lavagnoli
The influence of unsteady wakes incoming from the upstream stages is of high relevance in modern high-speed, low-pressure turbines (LPT) operating at transonic exit Mach numbers and low Reynolds numbers for their potential to trigger transition and influence the separation of the boundary layer on the blade suction side. The aim of this paper is the experimental characterization of the influence of incoming wakes on the 2D aerodynamics of a high-speed LPT cascade operating at a low Reynolds number and transonic exit Mach number. A detailed analysis of the status of the flow along the blade under investigation and its impact on the profile loss are presented for a range of Mach numbers from 0.70 to 0.95 and Reynolds numbers from 70k to 120k under steady and unsteady inflow conditions. Tests were conducted at on- and off-design engine realistic conditions in the VKI S-1/C wind tunnel on the SPLEEN C1 transonic cascade. The wakes incoming from an upstream blade row have been replicated using a set of rotating bars, which shed wakes at an engine-representative reduced frequency (f+=0.95) and flow coefficient (Φ=0.80). A set of densely instrumented traversable blades were used to sample the surface pressure distributions. The development of the boundary layers along the blade suction side is examined through quasi-wall shear stress obtained with surface-mounted hot-film sensors. Wake traverses were carried out downstream of the cascade with a miniaturized L-shaped five-hole probe to characterize the blade losses. The introduction of periodic incoming wakes promotes variations in the flow topology over the blade. The effect on the suction side separation bubble is shown to depend on the exit flow conditions. At low Mach numbers, the incoming wakes determine a reduction in the size of the bubble; in contrast, this effect is not registered as the exit Mach number increases. Consistently, a high dependence of the unsteady wake effect on the profile loss on the exit Reynolds and Mach numbers is demonstrated.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030034
Authors: Matteo Dellacasagrande Edward Canepa Andrea Cattanei Mehrdad Moradi
The present work reports an experimental study of the leakage flow in a low-speed fan ring. Existing 2D Particle Image Velocimetry (PIV) measurements taken in a meridional plane in front of the rotor gap have been further processed and analyzed by means of the Proper Orthogonal Decomposition (POD). Three values of the dimensionless pressure rise across the rotor have been investigated. Namely, attention has been focused on the intermediate case—the one for which a strong radial oscillation in the leakage flow has been observed: POD results have shown that, in this condition, the leakage flow exhibits periodic radial oscillations that are not correlated to the periodic blade passing. Moreover, such coherent motions have been found to promote turbulence transport at different radial positions, whereas rotor-related oscillations have a negligible effect in this sense. The present POD procedure can be generally applied to turbomachinery flows to characterize their unsteady behavior beside the classical phase-averaging methods based on rotor-related quantities. The present approach is novel for the study of leakage flow dynamics in axial fans.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030032
Authors: James Brind
This paper derives and validates an analytical model for acoustic boundary conditions on a can-annular gas turbine combustion system composed of discrete cans connected to an open annulus upstream of a turbine. The analytical model takes one empirical parameter: a connection impedance between adjacent cans. This impedance is extracted from time-marching computations of two-can sectors of representative combustors. The computations show that reactance follows the Rayleigh conductivity, while resistance takes a value of order 0.1 as a weak function of geometry. With a calibrated value of acoustic resistance, the analytical model reproduces can-to-can transfer functions predicted by full-annulus computations to within 0.03 magnitude at compact frequencies. Varying the combustor–turbine gap length, both model and computations exhibit a minimum in reflected energy, which drops by 63% compared to the datum gap. A parametric study yields a design guideline for gap length at the minimum reflected energy, allowing the designer to maximise transmission from the combustion system and reduce damping requirements.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030033
Authors: Hauke Witte Christoph Bode Jens Friedrichs
Typically installed in a rotor-only configuration, low-pressure axial fans discharge directly into a free atmosphere and the discharge shows a strong swirl component. Since such designs, without guide vanes, cannot convert the dynamic pressure in the swirl component back into static pressure, the dynamic pressure is usually considered a loss. However, the radial equilibrium shows that a significant part of the kinetic energy contained in this swirl component is recovered as static pressure in the free atmosphere. This additional pressure increase has been sparsely researched. A comparison between two configurations with and without outlet guide vanes allows for the formulation of an evaluation criterion of the rotor-only configuration. Utilizing this evaluation criterion, the investigation of velocity profiles corresponding to generic rotor designs shows promise in terms of pressure recovery for new designs.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030031
Authors: Christopher Hartmann Julia Schweikert François Cottier Ute Israel Jochen Gier Jens von Wolfersdorf
Experimental results for the transient heat transfer characteristics over a flat plate and over a plate with V-shaped ribs were compared to numerical results from a coupling environment applying FEM and CFD. In order to simulate transient effects in the cooling process of engine components during typical flight missions, the temperature and the velocity at the inlet of the channel were varied over time. The transient temperature distribution at the plate was measured using infrared thermography. Five different plate materials (perspex, PEEK, quartz, aluminum, and steel) were considered to investigate the influence of thermal conduction on the heat transfer between solid and fluid depending on the Biot number. The experimental results represent a reference database for a Python-based coupling environment applying CalculiX (FEM) and ANSYS CFX (CFD). The results were additionally compared to numerical results simulating the complete transient conjugated heat transfer with CFD. A good agreement between the numerical and the experimental results was achieved using different coupling sizes at different Biot numbers for the flat plate and the plate with V-shaped ribs.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030030
Authors: Clémence Rannou Julien Marty Geoffrey Tanguy Antoine Dazin
The tip gap region of an axial compressor rotor is a source of complex flows, inducing losses and stability issues. Recent works have proven the ability of blowing high-speed jets in the tip region to improve the surge margin of an axial compressor stage with a narrow tip gap configuration. However, the tip gap size can evolve during the compressor lifetime, possibly affecting its performance and operability. The objective is to evaluate the performance of an active flow control system on a compressor with different tip gap sizes. The present work is based on the single-stage compressor CME2 located at the Laboratory of Fluid Mechanics of Lille and equipped with actuators blowing at the rotor tip leading edge. Configurations with two different values of the tip gap to chord ratio (0.6% and 2.4%) are experimentally tested. RANS simulations are also performed. The effect of tip gap sizes and tip blowing on the flow topology and compressor performance is evaluated (surge margin improvement of the order of 200% for the larger tip gap size).
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030029
Authors: Mareen Derda Ferdinand Neumann Paul Uwe Thamsen
Even if wind tunnel tests and simulations have confirmed that tubercles can influence the behaviour of a profile, research in the field of axial pumps has so far been lacking. However, previous studies cannot be transferred to the application of axial pumps, since the requirements for the profile geometry as well as the Reynolds number range differ. The present study aims to address this research gap by performing a CFD simulation with a profile common for axial pumps, the Goe11K, testing four different tubercle configurations. At the same time, this simulation is a preliminary study for experimental tests. The results show that certain tubercle configurations improve the behaviour of the profile in the post-stall area, i.e., increase the lift of the profile at large angles of attack (α). In general, the curve of the profiles with tubercles runs more evenly, without the drastic drop in lift. This improved property comes at the expense of lower maximum lift and increased drag at lower α. With regard to the use of axial pumps, it can be concluded that there are advantages, particularly in the partial load range. These could ultimately enlarge the operation range of an axial pump.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030028
Authors: Markus Hundshagen Kevin Rave Michael Mansour Dominique Thévenin Romuald Skoda
A hybrid two-phase flow solver is proposed, based on an Euler–Euler two-fluid model with continuous blending of a Volume-of-Fluid method when phase interfaces of coherent gas pockets are to be resolved. In a preceding study on a two-dimensional bladed research pump with reduced rotational speed, the transition from bubbly flow to coherent steady gas pockets observed in optical experiments with liquid/gas flow could be well captured by the hybrid solver. In the present study, the experiments and solver validation are extended to an industrial-scale centrifugal pump with twisted three-dimensional blades and elevated design rotational speed. The solver is combined with a population balance model, and a scale-adaptive turbulence model is employed. Compared to the two-dimensional bladed pump, the transition from agglomerated bubbles flow to attached gas pockets is shifted to larger gas loading, which is well captured by the simulation. The pump head drop with increasing gas load is also reproduced, showing the hybrid solver’s validity for realistic pump operation conditions.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030027
Authors: Giacomo Zanetti Giovanna Cavazzini Alberto Santolin
This paper presents a numerical analysis of the influence of the von Karman vortex shedding at the blade trailing edge on the hydrodynamics of a recently installed small hydro Francis turbine manifesting very loud and high-frequency acoustic pulsations when operating close to the nominal load. A reduced single-passage numerical model is developed to reduce the computational effort of the simulation while ensuring high accuracy in the assessment of fluid flow. The accuracy of the proposed numerical approach is investigated by comparing the frequency spectrum of the experimentally acquired acoustic frequency and the numerical pressure signals, confirming the nature of the machine’s vibrations. The validated numerical model represents a useful tool for an in-depth analysis of the machine’s hydrodynamics in the preliminary design phases. The proposed approach represents a valid alternative to the traditional correlation-based approach for the evaluation of the von Karman shedding frequency with less computational effort compared with a transient simulation of the entire machine.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030026
Authors: Simon Joßberger Stefan Riedelbauch
Double-regulated Kaplan turbines with adjustable guide vanes and runner blades offer a high degree of flexibility and good efficiency for a wide range of operating points. However, this also leads to a complex geometry and flow guidance with, for example, vortices of different sizes and strengths. The flow in a draft tube is especially challenging to simulate mainly due to flow phenomena, like swirl, separation and strong adverse pressure gradients, and a strong dependency on the upstream flow conditions. Standard simulation approaches with RANS turbulence models, a coarse mesh and large time step size often fail to correctly predict performance and can even lead to wrong tendencies in the overall behavior. To reveal occurring flow phenomena and physical effects, a scale-resolving hybrid RANS-LES simulation on a block structured mesh of about 400 million hexahedral elements of a double-regulated five-blade model Kaplan turbine is carried out. In this paper, first, the results of the ongoing simulation are presented. The major part of the simulation domain is running in LES mode and seems to be properly resolved. The validation of the simulation results with the experimental data shows mean deviations of less than 0.8% in the global results, i.e., total head and power, and a good visual agreement with the three-dimensional PIV measurements of the velocity in the cone and both diffuser channels of the draft tube. In particular, the trend of total head and the results for the draft tube differ significantly between the scale-resolving simulation and a standard RANS simulation. The standard RANS simulation exhibits a highly unsteady behavior of flow, which is not observed in the experiments or scale-resolving simulation.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030025
Authors: Xavier Flete Nicolas Binder Yannick Bousquet Sandrine Cros
In the current study, full-stage unsteady simulations were performed to investigate rotating instability inception mechanisms in a particularly large tip clearance centrifugal compressor with a vaneless diffuser and a volute. Four operating points along a speed line were analysed to understand the influence of the mass flow reduction on flow structures. Close to the peak efficiency, an unsteady interaction between the tip clearance vortices and splitter blades was observed. Considering other studies, the influence of the tip gap size was analysed. Then, a large-scale vortex shedding from the leading edges of the main blades was detected when the stage operated near the maximum pressure ratio. It was demonstrated that shed vortices were caused by the combination of the radial gradient of the tangential velocity under the tip vortex and the reverse backflow near the casing. Previous studies on axial compressors refer to these vortical structures as backflow vortices. These vortices cause a significant increase in the incidence angle in the tip region.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030024
Authors: Mario Carta Tiziano Ghisu Shahrokh Shahpar
Due to the increasingly high turbine inlet temperatures, heat transfer analysis is now, more than ever, a vital part of the design and optimization of high-pressure turbine rotor blades of a modern jet engine. The present study aimed to find out how shape deviation and in-service deterioration affect heat exchange patterns on the rotor blade. The rotor geometries used for this analysis are represented by a set of high-resolution 3D structured light scans of blades with the same number of in-service hours. An automatic meshing technique was employed to generate high-resolution meshes directly on the scanned rotor geometries, which captured all the surface features with high fidelity. Steady-state 3D RANS flow simulations with a k-ω SST turbulence model were conducted on a one-and-a-half stage computational domain of the scanned geometries. First, the distribution of the heat transfer coefficient was calculated for each blade; then, a correlation was sought between the heat transfer coefficient and parametrized shape deviation, to assess the impact of each parameter on HTC levels.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030023
Authors: Hamed Abdeh Giovanna Barigozzi Nicoletta Franchina
Off-design condition of a rotor blade cascade with and without platform cooling was experimentally investigated. The ability of the gas turbine to operate down to 50% to 20% of its nominal intake air flow rate has an important consequence in the change in the inlet incidence angle, which varied from nominal to −20°. Platform cooling through an upstream slot simulating the stator-to-rotor interface gap was considered. The impact of rotation on purge flow injection was simulated by installing fins inside the slot to give the coolant flow a tangential direction. Aerodynamic measurements to quantify the cascade aerodynamic loss and secondary flow structures were performed at Ma2is = 0.55, varying the coolant to main flow mass flow ratio (MFR%) and the incidence angle. The results show that losses strongly increase with MFR. A negative incidence allows a reduction in the overall loss even when coolant is injected with a high MFR. The more negative the incidence, the greater the loss reduction.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030022
Authors: Filippo Merli Nicolas Krajnc Asim Hafizovic Emil Göttlich
The efficiency assessment of a high-pressure turbine (HPT) stage is complicated by the presence of upstream and downstream purge flows. In fact, the efficiency calculation is often based on mass flow-averaged values of total temperature at the stage inlet and outlet planes. Moreover, the purge flow distribution in the annulus is usually unknown and therefore assumed to be uniform. This paper presents and applies an alternative method to calculate the efficiency of a fully purged HPT stage. Such a definition relies on seed gas concentration measurements at the HPT stage outlet plane to determine the outlet purge flow distribution. After comparing the alternative method to the standard definition (based on the assumption of uniform purge) for the nominal purge case, the efficiency variation between the case with nominal purge and the case without purge is investigated.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030021
Authors: Fabio Licheri Tiziano Ghisu Francesco Cambuli Pierpaolo Puddu
An experimental investigation of the local flow field in a Wells turbine has been conducted, in order to produce a detailed analysis of the aerodynamic characteristics of the rotor and support the search for optimized solutions. The measurements were conducted with a hot-wire anemometer (HWA) probe, reconstructing the local three-dimensional flow field both upstream and downstream of a small-scale Wells turbine. The multi-rotation technique has been applied to measure the three velocity components of the flow field for a fixed operating condition. The results of the investigation show the local flow structures along a blade pitch, highlighting the location and radial extension of the vortices which interact with the clean flow, thus degrading the turbine’s overall performance. Some peculiarities of this turbine have also been shown, and need to be considered in order to propose modified solutions to improve its performance.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030020
Authors: Filippo Merli Nicolas Krajnc Asim Hafizovic Marios Patinios Emil Göttlich
The purpose of the paper is to characterize the aerodynamic behavior of a rotor-downstream hub cavity rim seal in a high-pressure turbine (HPT) stage. The experimental data are acquired in the Transonic Test Turbine Facility at the Graz University of Technology: the test setup includes two engine-representative turbine stages (the last HPT stage and first LPT stage), with the intermediate turbine duct in between. All stator-rotor cavities are supplied with purge flows by a secondary air system, which simulates the bleeding air from the compressor stages of the real engine. The HPT downstream hub cavity is provided with wall taps and pitot tubes at different radial and circumferential locations, which allows the performance of steady pressure and seed gas concentration measurements for different purge mass flows and HPT vanes clocking positions. Moreover, miniaturized pressure transducers are adopted to evaluate the unsteady pressure distribution, and an oil flow visualization is performed to retrieve additional information on the wheel space structures. The annulus pressure asymmetry depends on the HPT vane clocking, but this is shown to have negligible impact on the minimum purge mass flow required to seal the cavity. However, the hub pressure profile drives the distribution of the cavity egress in the turbine channel. The unsteady pressure field is dominated by blade-synchronous oscillations. No non-synchronous components with comparable intensity are detected.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8030019
Authors: Kenichiro Takeishi Robert Krewinkel
In the coming carbon-neutral era, industrial gas turbines (GT) will continue to play an important role as energy conversion equipment with high thermal efficiency and as stabilizers of the electric power grid. Because of the transition to a clean fuel, such as hydrogen or ammonia, the main modifications will lie with the combustor. It can be expected that small and medium-sized gas turbines will burn fewer inferior fuels, and the scope of cogeneration activities they are used for will be expanded. Industrial gas turbine cycles including CCGT appropriate for the carbon-neutral era are surveyed from the viewpoint of thermodynamics. The use of clean fuels and carbon capture and storage (CCS) will inevitably increase the unit cost of power generation. Therefore, the first objective is to present thermodynamic cycles that fulfil these requirements, as well as their verification tests. One conclusion is that it is necessary to realize the oxy-fuel cycle as a method to utilize carbon-heavy fuels and biomass and not generate NOx from hydrogen combustion at high temperatures. The second objective of the authors is to show the required morphology of the cooling structures in airfoils, which enable industrial gas turbines with a higher efficiency. In order to achieve this, a survey of the historical development of the existing cooling methods is presented first. CastCool® and wafer and diffusion bonding blades are discussed as turbine cooling technologies applicable to future GTs. Based on these, new designs already under development are shown. Most of the impetus comes from the development of aviation airfoils, which can be more readily applied to industrial gas turbines because the operation will become more similar. Double-wall cooling (DWC) blades can be considered for these future industrial gas turbines. It will be possible in the near future to fabricate the DWC structures desired by turbine cooling designers using additive manufacturing (AM). Another conclusion is that additively manufactured DWC is the best cooling technique for these future gas turbines. However, at present, research in this field and the data generated are scattered, and it is not yet possible for heat transfer designers to fabricate cooling structures with the desired accuracy.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8020018
Authors: David Beck Paul Uwe Thamsen
Especially in the field of sewage pumps, the design of radial impellers focuses not only on maximum efficiency but also on functionality in terms of susceptibility to clogging by fibrous media. In general, the efficiency of sewage impellers is significantly lower than that of clear water impellers. These sewage impellers are designed with a low number of blades to ensure that fibrous media can be pumped. This paper describes the methodology of an optimisation for a sewage impeller. The optimisation is carried out on a semi-open two-channel impeller as an example. Therefore, a new impeller is designed for a given volute casing. Based on a basic design for given boundary conditions, the impeller is verified by means of numerical simulation. The manufactured impeller is then tested on the test rig to verify the simulation. With regard to the optical investigations, the clogging behaviour of the impeller is specifically improved over three different modifications in order to finally present an impeller with good efficiency and a low clogging tendency.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8020017
Authors: Youngkuk Yoon Seung Jin Song
Cavitation instabilities can induce axial and circumferential vibrations, as well as noise in turbopump inducers. Therefore, the purpose of the present study is to investigate the mechanism of cavitation instability. The flow field near the two-bladed inducer leading edge under alternate blade cavitation was experimentally investigated using particle image velocimetry (PIV). It was found that the tip leakage vortex cavitation draws the flow toward its region of collapse and induces a negative change in the incidence to the adjacent blade. Moreover, this blade-to-blade interaction was identified as the main cause of alternate blade cavitation. Furthermore, it was demonstrated that this blade-to-blade interaction is strongest when the cavity collapse occurs in the inducer throat area, where the leading edge of the following blade is located.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8020016
Authors: Gerard Bois
Gas–liquid mixtures are present in numerous industrial applications, such as in the process industry, oil production and transport with natural gas, deep-sea extraction, and irrigation. Any pump may have to carry multiphase flows. However, the present document is related to non-miscible liquid/gas flow transport analysis in centrifugal pumps because which topic can be a more challenging task compared with axial and mixed flow machines due to specific body force and buoyancy actions and large density differences between the phases. The present document first introduces the main usual gas–liquid two-phase definitions and simplifications. A dimensional analysis introduces the main flow variables and parameters that are used for pumps. Basic physical aspects of flow motion in an impeller channel are explained, and a rapid description of two-phase flow patterns in radial flow pumps is described. Finally, a review of simplified empirical and semi-empirical analytical models is proposed with their limitations.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8020015
Authors: Markus Hundshagen Romuald Skoda
Predicting pump performance and ensuring operational reliability under two-phase conditions is a major goal of three-dimensional (3D) computational fluid dynamics (CFD) analysis of liquid/gas radial centrifugal pump flows. Hence, 3D CFD methods are increasingly applied to such flows in academia and industry. The CFD analysis of liquid/gas pump flows demands careful selection of sub-models from several fields in CFD, such as two-phase and turbulence modeling, as well as high-quality meshing of complex geometries. This paper presents an overview of current CFD simulation strategies, and recent progress in two-phase modeling is outlined. Particular focus is given to different approaches for dispersed bubbly flow and coherent gas accumulations. For dispersed bubbly flow regions, Euler–Euler Two-Fluid models are discussed, including population balance and bubble interaction models. For coherent gas pocket flow, essentially interface-capturing Volume-of-Fluid methods are applied. A hybrid model is suggested, i.e., a combination of an Euler–Euler Two-Fluid model with interface-capturing properties, predicting bubbly flow regimes as well as regimes with coherent gas pockets. The importance of considering scale-resolving turbulence models for highly-unsteady two-phase flow regions is emphasized.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8020014
Authors: Alin Ilie Bosioc Raul-Alexandru Szakal Adrian Stuparu Romeo Susan-Resiga
The current requirements of industrialized countries require the use of as much renewable energy as possible. One significant problem with renewable energy is that the produced power fluctuates. Currently, the only method available for energy compensation in the shortest time is given by hydroelectric power plants. Instead, hydroelectric power plants (especially the plants equipped with hydraulic turbines with fixed blades) are designed to operate in the vicinity of the optimal operating point with a maximum ±10% deviation. The energy market requires that hydraulic turbines operate in an increasingly wide area between −35% to 20% from the optimum operating point. Operation of hydraulic turbines far from the optimum operating point involves the appearance downstream of the turbine of a decelerated swirling flow with hydraulic instabilities (known in the literature as the vortex rope). The main purpose of this paper is to investigate numerically a new concept by using a free runner downstream on the main hydraulic runner turbine more precisely in the draft tube cone. The free runner concept requires rotations at the runaway speed with vanishing mechanical torque. The main purpose is to redistribute the total pressure and the moment between the shaft and the periphery. In addition, the free runner does not modify the operating point of the main hydraulic turbine runner.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8020013
Authors: Philipp Dietrich Marc Schneider
In applications, the acoustics of fans can differ significantly from the measurements of the standalone fan. This is due to disturbed inflow conditions, for example, caused by a heat exchanger upstream of an axial fan. Resolving the complex geometry and dimensions of typical heat exchangers in aeroacoustic scale-resolving simulations leads to a very high computation effort, which is currently not economically feasible. Turbulence reconstruction tools, such as the FRPM, provide the possibility to model the turbulent inflow conditions, thereby avoiding the representation of the heat exchanger in the aeroacoustic simulations. This approach is tested on a benchmark experiment of a ducted fan with an upstream turbulence grid.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8020012
Authors: Daniel Conrad Jonathan Mayer Erik Reichert
In many air conditioning applications fan arrays offer an increasingly popular alternative to single large fans due to redundancy and ease of maintainability. Additionally, there is the possibility to dynamically resize the array by selectively turning off a number of fans. In this work, a new method for the optimal control of such fan arrays is derived with the goal to minimize the overall power consumption, i.e., maximizing the system efficiency. The approach is universal in the sense that a fan array can be composed of any number, size, and type of fans or mixtures thereof. We explore the achievable power savings for a real world example by applying the method. Moreover, we give an outline of the optimal design of fan arrays and future work.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8020011
Authors: Stefan aus der Wiesche
The rising number of applications of the organic Rankine cycle (ORC) or supercritical CO2 (sCO2) power systems have shaped a new branch of fluid mechanics called non-ideal compressible fluid dynamics (NICFD). This field of fluid mechanics is concerned with flows of vapors or gases, which are characterized by substantial deviations from the perfect gas model. In extreme cases, even non-classical gas dynamic phenomena could occur. Although these non-ideal compressible flows are the subject of sophisticated numerical simulation studies today, there is also a growing need for experimental data for validating purposes. In the last couple of years, new experimental test rigs designed for investigating non-ideal compressible fluid dynamics have been developed and commissioned. Classical practical measurement techniques are currently being re-developed and applied to non-ideal compressible flows. Despite its substantial relevance, information about these measurement techniques and their differences from conventional methods in the open literature is scarce. The present review article is an attempt to reduce that gap. After briefly discussing the thermodynamics and fluid dynamics of non-ideal compressible flows, the currently available test rigs and their utilized measurement techniques are reviewed. This review discusses schlieren optical investigations, pneumatic and laser-optical methods, and hot-wire anemometry for non-ideal compressible flows.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8010010
Authors: Lukas Sandmaier Peter Meusburger Helmut Benigni
The complex flow conditions in Pelton turbines make it challenging to gain detailed insight into the local flow processes. However, CFD methods offer vast potential for developing and optimising Pelton turbines due to these flow conditions. In a comprehensive examination, a six-nozzle prototype Pelton turbine with 19 buckets has been investigated using 3D CFD simulations. First, the steady simulations of the manifold and the unsteady runner simulation have been performed with a mesh-based, commercial CFD code, whereby a two-equation turbulence model and the homogeneous two-phase model were used. Then, to limit the simulation time, symmetry was applied in the runner simulation, and also a strategic definition of the mesh element size in selected blocks of higher interest. Subsequently, the simulation results were analysed. Based on the first simulation results, the geometry of the distributor was modified in an iterative process to reduce losses and improve the jet shape. For the improvement of the latter, a characteristic number was introduced to quantify the secondary flows upstream of the nozzles, which act negatively on the jet shape. Furthermore, the results of the runner simulation were analysed with special regard to the jet-bucket interaction from the start to the end of the impingement cycle of a particular bucket. Finally, a potential efficiency increase could be derived from the summary.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8010009
Authors: Lorenzo Tieghi Giovanni Delibra Johan van der Spuy Alessandro Corsini
Air-cooled condensers (ACCs) are commonly found in power plants working with concentrated solar power or in steam power plants operated in regions with limited water availability. In ACCs, the flow of air is driven toward the heat exchangers by axial fans that are characterized by large diameters and operate at very high mass flow rates with a near-zero static pressure rise. Given the overall requirements in steam plants, these fans are subjected to inflow distortions, unstable operations, and are characterized by high noise emissions. Previous studies show that leading edge bumps in the tip region of axial fans can effectively reduce the sound pressure levels without affecting the static efficiency. Nevertheless, the effects of this treatment in terms of flow patterns and heat exchange in the whole ACC system were not investigated. In this work, the effect of leading edge bumps on the flow patterns is analyzed. Two RANS simulations were carried out using OpenFOAM on a simplified model of the air-cooled condenser. The fans are simulated using a frozen rotor approach. Turbulence modeling relies on the RNG k-epsilon model. The fan is characterized by a diameter of 7.3 m and a 333 m3/s volumetric flow rate at the design point. The presence of the heat exchanger is modeled using a porous medium. The comparison between the flow fields clearly exerts that the modified blade is responsible for the redistribution of radial velocities in the rotor region. This drastically reduces the losses related to the installation of the fan in a real configuration.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8010008
Authors: Jiangnan Zhang Mehrdad Zangeneh
In this paper, we present the design and optimization of a centrifugal fan with requirements of maximizing the total-to-static pressure rise and total-to-static efficiency at two operating points and the maximum torque provided by the motor power using a 3D inverse design method, a DOE (design of experiment) study, an RSM (response surface model) and a MOGA (multi-objective genetic algorithm). The fan geometry is parametrized using 13 design parameters, and 120 different designs are generated. The fan performances of all the designs at two operating conditions are evaluated through steady-state CFD simulations. The resulting design matrix is used to create an RSM based on the Kriging method and MOGA is used to search the design space using the RSM and find the optimal design.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8010007
Authors: Thomas Carolus Konrad Bamberger
This study targets determining impellers of impeller-only axial fans with an optimal hub-to-tip ratio for the highest achievable total-to-static efficiency. Differently from other studies, a holistic approach is chosen. Firstly, the complete class of these fans is considered. Secondly, the radial distribution of blade sweep angle, stagger angle, chord length, and camber are varied to adapt the blades to the complex flow in the hub and tip regions. The tool being used is an optimization scheme with three key components: (i) a database created beforehand by Reynolds-averaged Navier–Stokes (RANS)-predicted performance characteristics of 14,000 designs, (ii) an artificial neural network as a metamodel for the fan performance as a function of 26 geometrical parameters, and (iii) an evolutionary algorithm for optimization, performed on the metamodel. Typically, the hub-to-tip ratios for the impellers proposed by the optimization scheme are smaller than those obtained by applying the classic design rules. A second outcome are the shapes of the blades, which are adapted for a minimum exit loss. These shapes deviate substantially from the classic and even the state-of-the-art “swept-only” or “swept with dihedral” designs. The chord length, stagger, and sweep angle are distributed from hub to tip in a complex manner. The inherent reason is that the scheme tries to minimize not only the dynamic exit loss but also frictional losses due to secondary flows in the hub and tip regions, which eventually results in the maximum achievable total-to-static efficiency. Upon request, the authors will provide the full geometry of the four impellers analysed in some detail in this study to any individual for experimental validation or further analysis of their performance.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8010006
Authors: Zhuo Wang Lin Du Xiaofeng Sun
An immersed boundary (IB) method is applied to study the effect of the blade–row gap in a low-speed single-stage compressor. The advantage of using an IB method is that the rotor/stator interface can be eliminated and, thus, the blade–row interaction can be considered at an extremely small gap. The IB method was modified to internal-flow problems, and the adaptive mesh refinement (AMR) technique, together with a wall model, used to facilitate the simulations for high Reynolds-number flows. The results showed that both the pressure rise and the efficiency were observed to be higher in the smaller-gap cases. Comparisons between the results of two gaps, 35%ca and 3.5%ca, are highlighted and further analysis at a specific flow coefficient showed that the increase of the stage performance was contributed to by the enhancement of rotor loading and the suppression to the flow separation of the stator. Correspondingly, the increases of the total pressure rise on the rotor and the stator outlets were observed to be 0.5% and 4.3%, respectively. Although the increase on the rotor outlet is much lower than that on the stator outlet, its significance is that a higher level of static pressure is formed near the hub of the gap, which, thus, reduces the adverse pressure gradient of this region in the stator passage. This improvement suppresses the flow separation near the hub of the stator and, thereby, results in a considerable increase to the pressure rise on the stator outlet as a consequence. The effect of the gap on unsteady pressure fluctuation is also presented.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8010005
Authors: Benjamin Torner Duc Viet Duong Frank-Hendrik Wurm
The correct computation of flows over rough surfaces in technical systems, such as in turbomachines, is a significant issue for proper simulations of their performance data. Once the flow over rough surfaces is adequately computed in these machines, simulations become more trustworthy and can replace experimental prototyping. Roughness modelling approaches are often implemented in a solver to account for roughness effects in flow simulations. In these approaches, the equivalent sand roughness ks must be defined as a characteristic parameter of the rough surface. However, it is difficult to determine the corresponding ks-value for a surface roughness. In this context, this paper shows a novel and time-efficient numerical method, the discrete porosity method (DPM), which can be used to determine the ks-value of a rough surface. Applying this method, channel flow simulations were performed with an irregularly distributed cast iron surface from a turbopumps volute. After identifying the fully rough regime, the equivalent sand roughness was determined and a match with ks-values from literature data was found. Subsequently, the established ks-value for cast iron was used in a turbopump simulation with rough walls. The performance data of the pump were validated by experiments and a good agreement between the experimental and simulated performance data was found.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8010004
Authors: Johannes Brötz Christian Schänzle Peter F. Pelz
The efficiency definition allows us to compare two machines with each other. In general, the efficiency is defined as the ratio of usable power to the required power. This raises the question: what is the usable power? Most engineers discuss efficiency on the basis of the energy balance, i.e., the first law of thermodynamics. In this paper, we derive the exegetic efficiency taking the second law of thermodynamics into account. Exergy analysis takes into account work and heat and is able to model reality very accurately. On this basis, a comparison between the isentropic and exergetic efficiencies is given. A high-pressure radial fan is used as an example, and the differences are discussed. Therefore, measurements of a non-adiabatic fan are evaluated, and the role of the heat flux in the environment is discussed. The investigations show that a relevant difference between the isentropic and exergetic efficiencies becomes apparent in the partial-load range with high-pressure build-up. The thermal energy contained in the flow belongs proportionally to the exergy, i.e., the working capacity of the gas relative to its environment. For a standard such as ISO 5801 “Fans—Performance testing using standardized airways”, the efficiency must not only be physically correct, it must also be simple and practical. Against this background, the outlook of this paper discusses when and which efficiency definition is appropriate and best suited for a standard.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8010003
Authors: Zichen Yan Jianzhong Sun Yang Yi Caiqiong Yang Jingbo Sun
Data analysis is an important part of aero engine health management. In order to complete accurate condition monitoring, it is necessary to establish more effective analysis tools. Therefore, an integrated algorithm library dedicated for engine anomaly detection is established, which is PyPEFD (Python Package for Engine Fault Detection). Different algorithms for baseline modeling, anomaly detection and trend analysis are presented and compared. In this paper, the simulation data are used to verify the function of the anomaly detection algorithms, successfully completing the detection of multiple faults and comparing the accuracy algorithm under different conditions.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8010002
Authors: IJTPP Editorial Office IJTPP Editorial Office
High-quality academic publishing is built on rigorous peer review [...]
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp8010001
Authors: Felix Czwielong Stefan Becker
A novel active turbulence grid of the Institute of Fluid Mechanics at FAU Erlangen-Nuremberg is introduced. The focus of this grid is not on basic investigations of fluid mechanics, as is usually the case with active turbulence grids, but the generation of defined inflow conditions for axial fans. Thus, by means of the active turbulence grid, individual turbulence characteristics in the flow to the fan can be changed; therefore, fundamental interactions between the flow mechanics at the axial fan and the sound radiation can be analyzed. In addition, the replication of the flow fields of heat exchangers by the active turbulence grid is the focus of the investigations. The investigations showed that it is possible to use the active turbulence grid to generate defined inflow conditions for axial fans. It was also possible to reproduce the heat exchanger flow fields both for the mean turbulence values and for the spatial distributions. It was found that the grid induces tonal components due to the drive motors, but also that the inherent noise has no significant influence on the spectrum of the fans under investigation. Based on selected turbulence characteristics, direct correlations were found between the spatial distribution of the turbulence level and sound radiation at the first blade passing frequency of the axial fan. As the variance of the turbulence level increases, the sound radiation of the tonal components becomes more pronounced. The total sound pressure level, however, is mainly determined by the low-frequency broadband sound. A linear relationship between the spatial mean value of the turbulence level and the total sound pressure level was found for the investigated axial fan.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7040037
Authors: Frieder Lörcher Sandra Hub Marlène Sanjosé Stéphane Moreau
For a backward curved centrifugal fan, reducing volume flow rate from design operating point towards part load yields an increase in noise emission together with a reduction of efficiency. The spectral content of the emerging noise emission can be characterized by a subharmonic hump with several harmonics. Based on narrow-band acoustic measurements and numerical Lattice-Boltzmann simulations, a deeper insight is sought after. Downstream unsteady flow patterns are identified to play a central role in this performance deterioration; and geometrical flow stabilization means are investigated.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7040036
Authors: Thomas H. Carolus
The number of air- and gas-handling fans in use today is large [...]
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7040035
Authors: Fredrik Marincowitz Michael Owen Jacques Muiyser Peter Holkers
Ambient wind has a negative effect on mechanical forced-draft direct air-cooled steam condenser (ACC) fan volumetric performance, and increases dynamic fan blade loading. Investigating these effects directly using on-site measurement or numerical analysis is complicated, and most previous work has focused on only one effect at the expense of the other. In this study, fan axial velocity inflow uniformity is identified as a single metric offering the potential to holistically qualify ACC fan operation under windy conditions. A 3 × 6 fan cell ACC was modelled with CFD using a blade element theory-based fan model, and clear relationships between the fan inflow uniformity index and both fan volumetric performance and dynamic blade loading were observed in the results. The same relationships were observed in on-site test data collected at a single ACC fan, thus validating the numerical results. The uniformity index can be used in both numerical and experimental work as a means of investigating both fan volumetric performance and dynamic blade loading with less computational and measurement complexity; it also offers a potentially useful means of quantifying the severity of fan operating conditions, to assist with more reliable case-specific fan design and selection.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7040034
Authors: Dipali Ghodake Marlène Sanjosé Stéphane Moreau Manuel Henner
The effect of blade sweep has been studied numerically with the Lattice Boltzmann Method on a family of low-speed free-vortex axial fans with sweeps of ±45°. Good overall aerodynamic agreement is first demonstrated on all fans at the design condition, particularly in the tip gap. The local larger wall-pressure fluctuations seen in the unswept and backward swept fans compared to the forward case are traced to the stronger tip vortices that remain in the rotational plane or even move upstream. These stronger and faster vortices interacting with the fan blades are then responsible for the larger noise levels observed in the acoustic spectra of these fans, and particularly for large subharmonic humps. Excellent agreement between experimental and numerical noise predictions is finally reported stressing the dominant tip noise.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7040033
Authors: Martin Ottersten Hua-Dong Yao Lars Davidson
In this study, three voluteless centrifugal fans are compared for their aeroacoustic performances. The tonal noise is predicted by coupling the IDDES with Formulation 1A of Farassat. The sources of the tonal noise at the blade passing frequency (BPF) are identified. It is found that the sources are related to the fan inlet gap, which introduces higher velocity intensities and turbulent fluctuations interacting with the blade leading edge. By redesigning the gap, the tonal noise at the BPF is reduced effectively.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7040032
Authors: Nicola Aldi Nicola Casari Michele Pinelli Alessio Suman Alessandro Vulpio Ottavio Mantovani Paolo Saccenti
In industrial applications such as chemical plants, cement factories, and glassmakers, large-sized centrifugal fans are commonly used for dust-laden flow processing. In many cases, the contamination is due to solid particles responsible for fouling and erosion issues. Erosion induces the reduction of mechanical resistance and, at the same time, the modification of the geometry and the surface characteristics of the internal flow path. The process works according to the characteristics of the erodent particles, such as dimension and hardness, which have to be coupled with the mechanical properties of the substrate, like hardness and roughness level. In addition to this, the intensity of the erosion depends on the dynamic characteristics of particles, especially velocity and impact angle. For these reasons, erosion-related issues are difficult predict and reduce. In an attempt to preserve the structural integrity of the internal walls, wear-resistant plates are positioned where the impacting contaminants are supposed to be more detrimental. In the present work, a combined experimental and numerical approach is proposed to evaluate the proper setup of wear-resistance plates over the flow path of a large-sized centrifugal fan. The results show how different regions (rotating and stationary walls) are subjected to different impact behavior, determining that the design of the position of the wear-resistant plate is not straightforward. Suggestions related to reducing the erosion intensity are reported, highlighting the possibility of designing the best compromise between erosion, performance, and costs.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7040031
Authors: Claus Händel
Fans are components in many different products and have been regulated since 2011 by the Eco-Design Regulation. A fan is typically not a final product but is used as a component in different applications, systems, and products. This study shows that it is helpful to target and regulate a component (possibly additionally) such a fan and that the Eco-Design Regulation of fans is an important driver of energy efficiency and has a significant impact. Regulating fans as a component stimulates the availability of efficient fans at reasonable prices and drives efficiency, also in cases where fans are implemented in other products where a fan’s efficiency does not dominate its performance. Since it was first implemented in 2013, the following savings in electrical energy were achieved: 12 GW electrical power, 150 TWh electrical energy, and 12 MT CO2. This is significant and a good example for regulation.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7040030
Authors: Huang Huang Mingming Yang Dingxi Wang
Flutter was encountered at part speeds in a scaled wide chord fan blisk designed for a civil aeroengine during a rig test when the fan bypass flow was throttled toward its stall boundary. Analysis of the blade tip timing measurement data revealed that the fan blades vibrated at the first flap (1F) mode with nodal diameters of two and three. To facilitate a further rig test and ultimately eliminate the flutter problem, a numerical campaign was launched to help understand the root causes of the flutter. Both the influence coefficient method (ICM) and the traveling wave method (TWM) were employed in the numerical investigation to analyze unsteady flows due to blade vibration, with the intention to corroborate different numerical results and take advantage of each method. To eliminate nonphysical reflections, a sponge layer with an inflated mesh size was used for the extended inlet and outlet regions. Steady flow field and unsteady flow field were examined to relate them to the blade flutter. The influences of vibration frequency, mass flow rate, shock, boundary layer separation and acoustic mode propagation behaviors on the fan flutter stability were also investigated. Particular attention was paid to the acoustic mode propagation behaviors.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7040029
Authors: Henrik Feuk Francesco Pignatelli Arman Subash Ruike Bi Robert-Zoltán Szász Xue-Song Bai Daniel Lörstad Mattias Richter
The surface temperature of a burner nozzle using three different pilot hardware configurations was measured using lifetime phosphor thermometry with the ZnS:Ag phosphor in a gas turbine model combustor designed to mimic the Siemens DLE (Dry Low Emission) burner. The three pilot hardware configurations included a non-premixed pilot injection setup and two partially premixed pilot injections where one had a relatively higher degree of premixing. For each pilot hardware configuration, the combustor was operated with either methane or hydrogen-enriched methane (H2/CH4: 50/50 in volume %). The local heating from pilot flames was much more significant for hydrogen-enriched methane compared with pure methane due to the pilot flames being in general more closely attached to the pilot nozzles with hydrogen-enriched methane. For the methane fuel, the average surface temperature of the burner nozzle was approximately 40 K higher for the partially premixed pilot injection configuration with a lower degree of mixing as compared to the non-premixed pilot injection configuration. In contrast, with the hydrogen-enriched methane fuel, the differences in surface temperature between the different pilot injection hardware configurations were much smaller due to the close-to-nozzle frame structure.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7040028
Authors: Kaleab Fetahi Sharanabasaweshwara A. Asundi Arthur C. Taylor
Presented herein is a comparative performance analysis of a novel turbofan engine with an auxiliary combustion chamber, nicknamed the TurboAux engine, against a turbojet engine, and a low bypass ratio turbofan engine with an afterburner is presented. The TurboAux engine is an adaption of the low-bypass ratio turbofan engine, but with secondary combustion in an auxiliary bypass annular combustion chamber for thrust augmentation. The TurboAux engine is envisioned with the desire to facilitate clean secondary burning of fuel at temperatures higher than in the main combustion chamber with air exiting the low-pressure compressor. The comparative study starts by analyzing the turbojet engine and its performance with and without an afterburner segment attached. In parallel, the conventional turbofan and its mixing counterpart are analyzed, also with and without an afterburner segment. A simple optimization analysis of a conventional turbofan is performed to identify optimal ‘fan’ pressure ratios for a series of low-bypass ratios (0.1 to 1.5). The optimal fan pressure ratios and their corresponding bypass ratios are adapted to demonstrate the comparative performance of the varying configurations of the TurboAux engine. The formulation and results are an attempt to make a case for charter aircrafts and efficient close-air-support aircrafts. The results yielded increased performance in thrust augmentation, but at the cost of a spike in fuel consumption. This trade-off requires more in-depth investigation to further ascertain the TurboAux’s utility.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7040027
Authors: Julia Schweikert Bernhard Weigand
A central task in aviation technology is the development of efficient cooling techniques for thermal highly loaded engine components. For an optimal design of the cooling mechanisms, the heat transfer characteristics have to be known and need to be describable. As a cooling concept for low-pressure turbine casings, complex systems of impinging jets are used in order to reduce blade tip clearances during the flight mission. In order to improve established theoretical model approaches, this paper presents a novel method for the experimental investigation of such a complex system with 200 impinging jets using infrared thermography. The presented experimental method uses a thin electrically heated chrome-aluminum foil as target plate. Modeling the transient effects inside the foil, small structures and high gradients in the heat transfer coefficient can be reproduced with good accuracy. Experimental results of the local heat transfer characteristics are reported for jet Reynolds numbers of Re=2000…6000. The influence of the jet-to-jet distance and the jet Reynolds number on the Nusselt numbers are quantified with Nu∼(S/D)−0.47 and Nu∼Re0.7. The results indicate a dependency of the flow regime for the relatively low jet Reynolds numbers, as it is known from literature.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7040026
Authors: Christoph Brandstetter Sina Stapelfeldt
The prediction accuracy of aeroelastic stability in fans and compressors depends crucially on the accuracy of the underlying aerodynamic predictions. The prevalent approach in the field solves the unsteady Reynolds-averaged Navier—Stokes equations in the presence of blade vibration. Given the unsteady, three-dimensional and often separated nature of the flow in the regimes of aeroelastic interest, the confidence in URANS methods is questionable. This paper uses the simple test case of a pitching symmetric aerofoil with a sharp leading edge to illustrate the challenges of aeroelastic modelling. It compares coupled numerical simulations against time-resolved experimental measurements. The unsteady aerodynamic response of the pitching blade and its dependency on tip-clearance flow and time-averaged incidence angle are analyzed. The results indicate that differences in the unsteady aerodynamics between different numerical approaches close to stall can have a significant impact on local aerodynamic damping. Furthermore, for the chosen test case there is a strong correspondence between the local quasi-steady and unsteady behaviour which weakens, but is still present, towards stall.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7030025
Authors: Marcello Manna
The COVID-19 pandemic has not prevented the regular development of the dissemination activities promoted by Euroturbo (www [...]
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7030024
Authors: Roland Rückert Dieter Peitsch
The present paper investigates the aerodynamic performance of a cantilevered tandem stator based on experiments conducted within a high speed annular test rig at the Technische Universitaet Berlin. A tandem blade in this context describes a double rowed stator configuration where the turning of the incoming flow is split up between two blades arranged in succession. For evaluation purposes, a conventional single bladed stator is used as reference. To provide machine relevant boundary conditions of cantilevered stator assemblies, the moving hub wall is recreated by a rotating disk. Overall, the tandem stator is able to achieve higher flow turning while keeping the total pressure losses below those of a single stator. It is found that the tandem stator in general behaves similar to the conventional stator. When installed in cantilevered fashion, both stator types benefit considerably in terms of loss reduction. Without the hub clearance and therefore absence of the clearance flow, each of the configurations suffered from severe corner separation. The tandem stator responds more sensitively to change in clearance height.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7030023
Authors: Nicolas Poujol Martin Buisson Pierre Duquesne Isabelle Trébinjac
In centrifugal compressors, Mild Surge (MS) leads to unstable operation. Previous experimental work on a centrifugal compressor designed and built by Safran Helicopter Engines (SafranHE) showed that MS corresponds to the pulsation of an alternate stall pattern at the Helmholtz frequency of the test rig on two channels in the radial diffuser. The present contribution experimentally investigates the impact of the Inlet Guide Vane (IGV) stagger angle on this alternate flow and numerically studies the topology of this pulsating alternate flow. The experimental investigation is performed with unsteady pressure sensors, and shows that the IGV stagger angle only impacts the pulsation frequency of the alternate flow pattern. This change is explained by the dependence of the Helmholtz frequency on the compressor inlet section. The topological analysis of the average flow field, computed from wall-resolved Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations, demonstrates that the saddle point (major critical point) in the corner hub/suction side of the stalled blade migrates upstream while staying in the corner if the mass flow rate decreases. One main blade over two is stalled on both sides because the flow originating from this corner separation circumvents the trailing edge and migrates upstream along the pressure side. In the simulation, the pulsation of the alternate stall is coupled with the reflection of acoustic waves on the inlet and outlet planes, regarded as an environmental effect.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7030022
Authors: Giovanna Barigozzi Hamed Abdeh Samaneh Rouina Nicoletta Franchina
Design of cooling systems for rotor platforms is critical due to the complex flow field and heat transfer phenomena related to the secondary flow structures originating at the blade leading edge. Horseshoe vortex and passage vortex are the fluid-dynamic features that largely influence the aerodynamic behaviour and the thermal protection level of the platform. The driving parameter is the coolant to mainstream momentum flux ratio, but several issues have to be considered in the design process of cooling technologies. As well acknowledged, an in-depth understanding of losses and heat transfer phenomena are deemed necessary to design effective cooling systems. In the present review, measurements and predictions on the behaviour of the HPT rotor cooled platform, obtained during the last two decades by several research groups, are gathered, described and analysed in terms of aerodynamic losses and heat transfer performance, and are compared with one another with respect to the effectiveness level that is ensured.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7030021
Authors: Pierre Duquesne Joffrey Chanéac Gabriel Mondin Jérôme Dombard
Boundary-layer flow separation is a common flow feature in many engineering applications. The consequences of flow separation in turbomachinery can be disastrous in terms of performance, stability and noise. In this context, flow separation is particularly difficult to understand because of its three-dimensional and confined aspects. Analyzing the skin friction lines is one key point to understanding and controlling this phenomenon. In the case of separation, the flow at the wall agglutinates around a manifold while the fluid from the boundary layer is ejected toward the flow away from the wall. The analysis of a three-dimensional separation zone based on topology is well addressed for a simple geometry. This paper aims at providing simple rules and methods, with a clear vocabulary based on mathematical background, to conduct a similar analysis with complex turbomachinery geometry (to understand a surface with a high genus). Such an analysis relies on physical principles that help in understanding the mechanisms of flow separation on complex geometries. This paper includes numerous typical turbomachinery surfaces: the stator row, vaneless diffuser, vaned diffuser, axial rotor and shrouded and unshrouded centrifugal impeller. Thanks to surface homeomorphisms, the generic examples presented can easily be converted into realistic shapes. Furthermore, classical turbomachinery problems are also addressed, such as periodicity or rotor clearance. In the last section, the proposed methodology is conducted on a radial diffuser of an industrial compressor. The flow at the wall is extracted from LES computations. This study presents the different closed separation zones in a high-efficiency operating condition.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7030020
Authors: Chao Zhang Matthew Janeway
Optimization methods have been widely applied to the aerodynamic design of gas turbine blades. While applying optimization to high-fidelity computational fluid dynamics (CFD) simulations has proven capable of improving engineering design performance, a challenge has been overcoming the prolonged run-time due to the computationally expensive CFD runs. Reduced-order models and, more recently, machine learning methods have been increasingly used in gas turbine studies to predict performance metrics and operational characteristics, model turbulence, and optimize designs. The application of machine learning methods allows for utilizing existing knowledge and datasets from different sources, such as previous experiments, CFD, low-fidelity simulations, 1D or system-level studies. The present study investigates inserting a machine learning model that utilizes such data into a high-fidelity CFD driven optimization process, and hence effectively reduces the number of required evaluations of the CFD model. Artificial Neural Network (ANN) models were trained on data from over three thousand two-dimensional (2D) CFD analyses of turbine blade cross-sections. The trained ANN models were then used as surrogates in a nested optimization process alongside a full three-dimensional Navier–Stokes CFD simulation. The much lower evaluation cost of the ANN model allows for tens of thousands of design evaluations to guide the search of the best blade profiles to be used in the more expensive, high-fidelity CFD runs, improving the progress of the optimization while reducing the required computation time. It is estimated that the current workflow achieves a five-fold reduction in computational time in comparison to an optimization process that is based on three-dimensional (3D) CFD simulations alone. The methodology is demonstrated on the NASA/General Electric Energy Efficient Engine (E3) high pressure turbine blade and found Pareto front designs with improved blade efficiency and power over the baseline. Quantitative analysis of the optimization data reveals that some design parameters in the present study are more influential than others, such as the lean angle and tip scaling factor. Examining the optimized designs also provides insight into the physics, showing that the optimized designs have a lower amount of pressure drop near the trailing edge, but have an earlier onset of pressure drop on the suction side surface when compared to the baseline design, contributing to the observed improvements in efficiency and power.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7030019
Authors: Hanxin Chen Shaoyi Li Menglong Li
Conventional signal processing methods such as Principle Component Analysis (PCA) focus on the decomposition of signals in the 2D time–frequency domain. Parallel factor analysis (PARAFAC) is a novel method used to decompose multi-dimensional arrays, which focuses on analyzing the relevant feature information by deleting the duplicated information among the multiple measurement points. In the paper, a novel hybrid intelligent algorithm for the fault diagnosis of a mechanical system was proposed to analyze the multiple vibration signals of the centrifugal pump system and multi-dimensional complex signals created by pressure and flow information. The continuous wavelet transform was applied to analyze the high-dimensional multi-channel signals to construct the 3D tensor, which makes use of the advantages of the parallel factor decomposition to extract feature information of the complex system. The method was validated by diagnosing the nonstationary failure modes under the faulty conditions with impeller blade damage, impeller perforation damage and impeller edge damage. The correspondence between different fault characteristics of a centrifugal pump in a time and frequency information matrix was established. The characteristic frequency ranges of the fault modes are effectively presented. The optimization method for a PARAFAC-BP neural network is proposed using a genetic algorithm (GA) to significantly improve the accuracy of the centrifugal pump fault diagnosis.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7020018
Authors: Alexander Johannes Hacks Dieter Brillert
In the sCO2-HeRo project, the Chair of Turbomachinery at the University of Duisburg-Essen developed, built and tested a turbomachine with an integral design in which the compressor, generator and turbine are housed in a single hermetic casing. However, ball bearings limited operation because their lubricants were incompatible with supercritical CO2 (sCO2) and they had to operate in gaseous CO2 instead. To overcome this problem, the turbomachine was redesigned built and tested in the sCO2-4-NPP project. Instead of ball bearings, magnetic bearings are now used to operate the turbomachine with the entire rotor in sCO2. This paper presents the revised design, focusing on the usage of magnetic bearings. It also investigates whether the sCO2 limits the operating range. Test runs show that increasing the density and rotational speed results in greater deflection of the rotor and greater forces on the bearings. Measurements are also analyzed with respect to influence of the density increase on the destabilizing forces in the rotor–stator cavities. The conclusion is that for the operation of the turbomachine, the control parameters of the magnetic bearings must be adjusted not only to the rotor speed, but also to the fluid density. This enabled successful operation of the turbomachine, which reached a speed of about 40,000 rpm during initial tests in CO2.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7020017
Authors: Valdo Pagès Pierre Duquesne Stéphane Aubert Laurent Blanc Pascal Ferrand Xavier Ottavy Christoph Brandstetter
The application of composite fans enables disruptive design possibilities but increases sensitivity to multi-physical resonance between aerodynamic, structure dynamic and acoustic phenomena. As a result, aeroelastic problems increasingly set the stability limit. Test cases of representative geometries without industrial restrictions are a key element of an open scientific culture but are currently non-existent in the turbomachinery community. In order to provide a multi-physical validation benchmark representative of near-future UHBR fan concepts, the open-test-case fan stage ECL5 was developed at Ecole Centrale de Lyon. The design intention was to develop a geometry with high efficiency and a wide stability range that can be realized using carbon fibre composites. This publication aims to introduce the final test case, which is currently fabricated and will be experimentally tested. The fan blades are composed of a laminate made of unidirectional carbon fibres and epoxy composite plies. Their structural properties and the ply orientations are presented. To characterize the test case, details are given on the aerodynamic design of the whole stage, structure dynamics of the fan and aeroelastic stability of the fan. These are obtained with a state-of-art industrial design process: static and modal FEM, RANS and LRANS simulations. Aerodynamic analysis focuses on performance and shows critical flow structures such as tip leakage flow, radial flow migration and flow separations. Mechanical modes of the fan are described and discussed in the context of aeroelastic interactions. Their frequency distribution is validated in terms of resonance risk with respect to synchronous vibration. The aeroelastic stability of the fan is evaluated at representative operating points with a systematic approach. Potential instabilities are observed far from the operating line and do not compromise experimental campaigns.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7020016
Authors: James Hammond Nick Pepper Francesco Montomoli Vittorio Michelassi
Computational Fluid Dynamics is one of the most relied upon tools in the design and analysis of components in turbomachines. From the propulsion fan at the inlet, through the compressor and combustion sections, to the turbines at the outlet, CFD is used to perform fluid flow and heat transfer analyses to help designers extract the highest performance out of each component. In some cases, such as the design point performance of the axial compressor, current methods are capable of delivering good predictive accuracy. However, many areas require improved methods to give reliable predictions in order for the relevant design spaces to be further explored with confidence. This paper illustrates recent developments in CFD for turbomachinery which make use of machine learning techniques to augment prediction accuracy, speed up prediction times, analyse and manage uncertainty and reconcile simulations with available data. Such techniques facilitate faster and more robust searches of the design space, with or without the help of optimization methods, and enable innovative designs which keep pace with the demand for improved efficiency and sustainability as well as parts and asset operation cost reduction.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7020015
Authors: Tina Unglaube Dieter Brillert
With an increase in fluid densities in centrifugal compressors, fluid-structure interaction and coupled acoustoelastic modes receive growing attention to avoid machine failure. Besides the vibrational behavior of the impeller, acoustic modes building up in the side cavities need to be understood to ensure safe and reliable operation. In a coupled system, these structure and acoustic dominant modes influence each other. Therefore, a comprehensive overview of frequency shift effects in rotor-cavity systems is established based on findings in the literature. Additionally, experimental results on coupled mode pairs in a rotor-cavity test rig with a rotating disk under varying operating conditions are presented. Measurement results for structure dominant modes agree well with theoretical predictions. The development of a forward and a backward traveling wave is demonstrated for each mode in case of disk rotation. Conducted experiments reveal the occurrence of weakly and strongly coupled mode pairs as frequency shifts are observed that cannot solely be explained by “uncoupled mode effects”, such as the added mass, speed of sound, and stiffening effect, but indicate an additional coupling effect. However, the hypothesis of a bigger frequency shift for stronger coupled modes cannot be corroborated consistently. Only for the strongly coupled four nodal diameter mode pair in the “wide cavity” setup, a coupling effect is clearly visible in the form of mode veering.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7020014
Authors: Yumin Liu Patrick Hendrick Zhengping Zou Frank Buysschaert
Empirical correlations are still fundamental in the modern design paradigm of axial turbines. Among these, the prominent Ainley and Mathieson correlation (Ainley D. and Mathieson G., 1951, “A Method of Performance Estimation for Axial-Flow Turbines,” ARC Reports and Memoranda No. 2974) and its derivatives, plays a crucial role. In this paper, the underlying assumptions of the aforementioned models are discussed by means of a descriptive review, whilst an attempt is made to enhance their reliability and, potentially, accuracy in performance estimations. Closer investigation reveals an intriguing misuse of the lift coefficient in the secondary loss. In light of this, an enhanced model that, notably, builds upon the Zweifel criterion and the vortex penetration depth concept is developed and discussed. The obtained accuracy is subsequently assessed through CFD computations, employing a database comprising 109 cascades. The results indicate a 50% probability of achieving the ±15% error interval, which is twice as good as the most recent Aungier model (Aungier R., 2006, “Turbine Aerodynamics: Axial-Flow and Radial-Inflow Turbine Design and Analysis”, ASME Press, New York). Furthermore, the reliability of the proposed model is demonstrated by a reconstruction of the Smith chart, on the one hand, and a performance analysis, on the other. The reconstruction exhibits contours that conform to the original. The results of the performance study are compared with the CFD solutions of eight cascades working in off design conditions and confirm the need of the additionally included turbine design parameters, such as the axial velocity and the meanline radius ratios.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7020013
Authors: Jonah Harris Bharat Lad Sina Stapelfeldt
The increased demands of compact modern aero engine architectures have highlighted the problem of outlet guide vane (OGV) buffeting in off-design conditions. This structural response to aerodynamic excitations is characterised by increased vibration, risking structural fatigue. Investigations focused on understanding, mitigation and avoidance are therefore of high priority. OGV buffet is a type of transonic buffet caused by unsteady shock movement, but the exact parameters driving it are not fully understood. To try and understand them, this paper examines the buffet of a quasi-2D OGV geometry. Parametric studies of the incidence angle and inlet Mach number were performed. Forcing frequencies for both studies were found to be close to the experimentally detected frequency of vibration in the first bow mode, which demonstrates that buffet is driven by quasi-2D flow features. Increasing the inlet Mach number increased the dominant forcing frequency, whereas increasing the incidence yielded little change. Profiles of unsteady pressure amplitudes were shown to smoothly increase in magnitude with an increasing incidence and inlet Mach number.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7020012
Authors: Stephan Sundermeier Maximilian Passmann Stefan aus der Wiesche Eugeny Y. Kenig
In numerous turbomachinery applications, e.g., in aero-engines with regenerators for improving specific fuel consumption (SFC), heat exchangers with low-pressure loss are required. Pil low-plate heat exchangers (PPHE) are a novel exchanger type and promising candidates for high-speed flow applications due to their smooth profiles avoiding blunt obstacles in the flow path. This work deals with the overall system behavior and gas dynamics of pillow-plate channels. A pillow-plate channel was placed in the test section of a blow-down wind tunnel working with dry air, and compressible flow phenomena were investigated utilizing conventional and focusing schlieren optics; furthermore, static and total pressure measurements were performed. The experiments supported the assumption that the system behavior can be described through a Fanno–Rayleigh flow model. Since only wavy walls with smooth profiles were involved, linearized gas dynamics was able to cover important flow features within the channel. The effects of the wavy wall structures on pressure drop and Mach number distribution within the flow path were investigated, and a good qualitative agreement with theoretical and numerical predictions was found. The present analysis demonstrates that pressure losses in pillow-plate heat exchangers are rather low, although their strong turbulent mixing enables high convective heat transfer coefficients.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7010011
Authors: Leander Hake Felix Reinker Robert Wagner Stefan aus der Wiesche Markus Schatz
Results from an experimental profile loss study are presented of an additive manufactured linear turbine cascade placed in the test section of a closed-loop organic vapor wind tunnel. This test facility at Muenster University of Applied Sciences allows the investigation of high subsonic and transonic organic vapor flows under ORC turbine flow conditions at elevated pressure and temperature levels. An airfoil from the open literature was chosen for the cascade, and the organic vapor was Novec 649TM. Pitot probes measured the flow field upstream and downstream of the cascade. The inflow turbulence level was 0.5%. The roughness parameters of the metal-printed blades were determined, and the first set of flow measurements was performed. Then, the blade surfaces were further finished, and the impact of roughness on profile losses was assessed in the second flow measurement set. Although the Reynolds number level was relatively high, further surface treatment reduces the profile loss noticeably in organic vapor flows through the printed cascade.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7010010
Authors: Joseph Moubogha Moubogha Gabriel Margalida Pierric Joseph Olivier Roussette Antoine Dazin
Stall and surge are strong limitations in the operating range of compressors and thus one of the major limits of jet engine performance. A promising way to push the stability limit of compression machines is to inject a small amount of flow at the blade tip to alter the physical mechanism responsible for stall onset. This study focuses on the experimental performance of such a system. To do so, an axial compressor test bench was equipped with 40 actuators connected to an auxiliary pressurised air supply system. They were able to generate high-speed jet blowing just at the tip of the rotor blades. The opening of each actuator was controlled by an electromagnetic valve. This allowed generating continuous or pulsed jets with frequencies up to 500 Hz at different duty cycles. The performance of the control system was investigated for various control strategies, where the injected flow rate, the injection angle, the number of injectors, the jet frequency and the duty cycle were systematically varied. This paper is concluded by a study of the energy balance of the system for various configurations. To the best of the authors’ knowledge, this constitutes a rarely seen analysis in the literature.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7010009
Authors: Florian Felix Lapp Sebastian Schuster Simon Hecker Dieter Brillert
This paper presents experimental data on shear-stress-driven liquid water films on a horizontal plate formed by the condensation of superheated steam. The experimental results were obtained in the Experimental Multi-phase Measurement Application (EMMA) at the University of Duisburg-Essen. The liquid film thickness was spatially and temporally investigated with an optical measurement system. Furthermore, the resulting local heat transfer coefficient in the case of film condensation was determined for a variety of steam velocities and temperatures. Subsequently, the presented data are compared to the results of an analytical condensation model for shear-stress-driven liquid films developed by Cess and Koh. Thus, the model is qualitatively validated, with explicable remaining disparities between the model and experiment that are further discussed. The presented results are an important contribution to the contemporary research into steady-state, single-component multiphase flow considering phase-change phenomena including heat transfer.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7010008
Authors: Andrea Cassinelli Andrés Mateo Gabín Francesco Montomoli Paolo Adami Raul Vázquez Díaz Spencer J. Sherwin
Reynolds-Averaged Navier–Stokes (RANS) methods continue to be the backbone of CFD-based design; however, the recent development of high-order unstructured solvers and meshing algorithms, combined with the lowering cost of HPC infrastructures, has the potential to allow for the introduction of high-fidelity simulations in the design loop, taking the role of a virtual wind tunnel. Extensive validation and verification is required over a broad design space. This is challenging for a number of reasons, including the range of operating conditions, the complexity of industrial geometries and their relative motion. A representative industrial low pressure turbine (LPT) cascade subject to wake passing interactions is analysed, adopting the incompressible Navier–Stokes solver implemented in the spectral/hp element framework Nektar++. The bar passing effect is modelled by leveraging a spectral-element/Fourier Smoothed Profile Method. The Reynolds sensitivity is analysed, focusing in detail on the dynamics of the separation bubble on the suction surface as well as the mean flow properties, wake profiles and loss estimations. The main findings are compared with experimental data, showing agreement in the prediction of wake traverses and losses across the entire range of flow regimes, the latter within 5% of the experimental measurements.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7010007
Authors: George Hill Julian Gambel Sabine Schneider Dieter Peitsch Sina Stapelfeldt
Modern aeroengine designs strive for peak specific fuel and thermal efficiency. To achieve these goals, engines have more highly loaded compressor stages, thinner aerofoils, and blended titanium integrated disks (blisks) to reduce weight. These configurations promote the occurrence of aeroelastic phenomena such as flutter. Two important parameters known to influence flutter stability are the reduced frequency and the ratio of plunge and pitch components in a combined flap mode shape. These are used as design criteria in the engine development process. However, the limit of these criteria is not fully understood. The following research aims to bridge the gap between semi-analytical models and modern compressors by systematically investigating the flutter stability of a linear compressor cascade. This paper introduces the plunge-to-pitch incidence ratio, which is defined as a function of reduced frequency and pitch axis setback for a first flap (1F) mode shape. Using numerical simulations, in addition to experimental validation, aerodynamic damping is computed for many modes to build stability maps. The results confirm the importance of these two parameters in compressor aeroelastic stability as well as demonstrate the significance of the plunge-to-pitch incidence ratio for predicting the flutter limit.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7010006
Authors: Anne-Lise Fiquet Stéphane Aubert Nicolas Buffaz Agathe Vercoutter Christoph Brandstetter
Non-synchronous blade vibrations have been observed in an experimental multi-stage high-speed compressor setup at part-speed conditions. A detailed numerical study has been carried out to understand the observed phenomenon by performing unsteady full-annulus Reynolds-Averaged Navier–Stokes (RANS) simulations of the whole setup using the solver elsA. Several operating conditions have been simulated to observe this kind of phenomena along a speedline of interest. Based on the simulation results, the physical source of the non-synchronous blade vibration is identified: An aerodynamic disturbance appears in a highly loaded downstream rotor and excites a spinning acoustic mode. A “lock-in” phenomenon occurs between the blade boundary layer oscillations and the spinning acoustic mode. The establishment of axially propagating acoustic waves can lead to a complex coupling mechanism and this phenomenon is highly relevant in understanding the multi-physical interactions appearing in modern compressors. It is shown that aerodynamic disturbances occurring downstream can lead to critical excitation of rotor blades in upstream stages due to an axially propagating acoustic wave. The paper includes the analysis of a relevant transient test and a detailed analysis of the numerical results. The study shows the capability and necessity of a full-annulus multistage simulation to understand the phenomenon.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7010005
Authors: Michael van de Noort Peter Ireland
The high pressure turbine nozzle guide vane of a modern aeroengine experiences large heat loads and thus requires both highly effective internal and external cooling. This can be accomplished with double-wall effusion cooling, which combines impingement, pin-fin and effusion cooling. The combination of three cooling mechanisms causes high pressure losses, increasing potential for the migration of coolant towards low pressure regions, subsequently starving effusion holes on the leading edge of coolant supply. This paper presents a low order flow network model to rapidly assess the pressure and mass flow distributions through such cooling schemes for a flexible set of geometric and flow conditions. The model is subsequently validated by a series of experiments with varying mainstream pressure gradients. Results from the model are used to indicate design parameters to reduce the effect of coolant migration, and to minimise the risk of destructive hot gas ingestion.
]]>International Journal of Turbomachinery, Propulsion and Power doi: 10.3390/ijtpp7010004
Authors: IJTPP Editorial Office IJTPP Editorial Office
Rigorous peer-reviews are the basis of high-quality academic publishing [...]
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