Search Results (65)

This work presents an extensive experimental and numerical analysis, aimed at investigating the impact of shelf-like fences applied on the suction side of a turbine nozzle guide vane. The cascade is constituted of vanes characterized by long chord and low aspect ratio, which are typical features of some LPT first stages directly downstream of an HPT, hence presenting high channel diffusion, especially near the tip. In particular, the present study complements existing literature by highlighting how blade fences positioned on the suction side can reduce the penetration of the large passage vortex. This is particularly effective in applications where flow turning is limited, the blades are lightly loaded at the front, and the horseshoe vortex is weak. The benefits of the present fence design in terms of losses and flow uniformity at the cascade exit plane have been demonstrated by means of a detailed experimental campaign carried out on a large-scale linear cascade in the low-speed wind tunnel installed in the Aerodynamics and Turbomachinery Laboratory of the University of Genova. Measurements mainly focused on the characterization of the flow field upstream and downstream of straight and fenced vane cascades using a five-hole pressure probe, to evaluate the impact of the device in reducing secondary flows. Furthermore, experiments were also adopted to validate both low-fidelity (RANS) and high-fidelity (LES) simulations and revealed the capability of both simulation approaches to accurately predict losses and flow deviation. Moreover, the accuracy in high-fidelity simulations has enabled an in-depth investigation of how fences act mitigating the effects of the passage vortex along the blade channel. By comparing the flow fields of the configurations with and without fences, it is possible to highlight the mitigation of secondary flows within the channel. Full article

This study utilizes Computational Fluid Dynamics (CFD) to optimize the aerodynamic performance of a Formula 1 (F1) car diffuser, investigating the effects of vane placements, end-flap positions, and other structural modifications. Diffusers are critical in managing airflow, enhancing downforce, and reducing drag, directly influencing vehicle stability and speed. Despite ongoing advancements, the interaction between diffuser designs and turbulent flow dynamics requires further exploration. A Three-Dimensional k-Omega-SST RANS-based CFD methodology was developed to evaluate the aerodynamic performance of various diffuser configurations using Star CCM+. The findings reveal that adding lateral vane parallel to the divergence section improved high-intensity fluid flow distribution within the main channel, achieving 13.49% increment in downforce and 5.58% reduction in drag compared to the baseline simulation. However, incorporating an airfoil cross-section flap parallel to the divergence end significantly enhances the car’s performance, leading to a substantial improvement in downforce while relatively small increase in drag force. This underscores the critical importance of precise flap positioning for optimizing aerodynamic efficiency. Additionally, the influence of adding flaps underneath the divergence section was also analyzed to manipulate boundary layer separation to achieve improved performance by producing additional downforce. This research emphasizes the critical role of vortex management in preventing flow detachment and improving diffuser efficiency. The findings offer valuable insights for potential FIA F1 2023 undertray regulation changes, with implications for faster lap times and heightened competitiveness in motorsports. Full article

Lead–Bismuth Eutectic (LBE) is a very dense medium whose specific gravity is more than 10 times that of water. The unsteady hydraulic exciting force generated by the rotor–stator interaction (RSI) is significantly increased in the LBE pump, which has an important influence on the stable operation of the pump. The clearance between the vaned diffuser inlet and the impeller outlet has great influence on the rotor–stator interaction. This paper studies the unsteady flow characteristics in pumps with different rotor–stator clearance in different flow rates and transported mediums. The results show that at the design point, the head and efficiency of the pump when transporting LBE are 3.52% and 8.05% higher than those when transporting water. The pressure fluctuation distribution is similar at different positions inside the pump when transporting LBE and water, but the dimensionless pressure fluctuation coefficient is slightly larger when transporting water. The radial force in the pump shows a larger amplitude of 6BPF frequency with small clearance ratios, and the frequency is related to the guide vane number. When the clearance ratio increases from 1.03 to 1.13, the amplitude of 6BPF keeps decreasing. The amplitude at a clearance ratio of 1.13 decreased to 4.7% of that at 1.03. The research presented in this paper could provide some references for the design of the clearance between the rotor–stator parts in the LBE pump. Full article

This study conducts a numerical analysis to understand the effect of flow through the impeller–diffuser side gap on the performance and internal flow of a centrifugal pump. Three-dimensional steady-state Reynolds-averaged Navier–Stokes simulations are performed, employing the shear stress transport turbulence model for turbulence closure. To analyze the effects of side-gap flow on the main passage flow, a simplified fluid domain for the side gap is constructed and applied with a one-dimensional loss model for the leakage flow. The numerical results are validated with experimental data for performance curves and velocity components at the diffuser inlet. For a detailed analysis of the leakage flow, flow simulations are carried out for three cases: flow absence, inflow, and outflow (leakage) in the impeller–diffuser gap. Significant performance deviations are observed according to the flow direction in the gap, and the detailed fluid flow structures are examined to assess its impact on the performance. Full article

The supersonic swirling device is a new apparatus that can be used for natural-gas liquefaction. The structure of the supersonic swirling device has an important impact on the liquefaction efficiency. Therefore, this study presents a structural design method for supersonic cyclones based on CFD theory. Using the production parameters of a liquefied natural gas (LNG) peak-shaving station as the study case, a detailed design and design comparison of each part of the supersonic swirling separator are carried out. An optimum LNG supersonic swirling separator design was obtained. To ensure that the designed supersonic swirling separator achieved better liquefaction effectiveness, it was ascertained that no large shockwaves were generated in the de Laval nozzle, the pressure loss on the swirler was small, and the swirler was able to produce a large centripetal acceleration. The opening angle of the diffuser and the length of the straight tube were designed considering the location at which normal shockwaves were generated. The location at which shockwaves are generated and the friction effect are important parameters that determine the gap size. With this design guidance, the optimal structural dimensions of the supersonic swirling device for a given processing capacity were determined as follows: a swirler with six vanes and an 8 mm wide channel; a 10D-long straight tube, an opening angle of 20° between the straight tube and the divergent section, and a gap size of 2 mm. Compared with “Twister II”, the new device has better liquefaction efficiency. Full article

Wide-flow centrifugal pumps are widely used in marine, petrochemical, and thermal power plants because of their good hydraulic performance. To enhance the hydraulic performance of wide-flow centrifugal pumps and thereby reduce energy consumption, in this study, an automatic optimization system for rotating machinery based on genetic algorithms was employed. Initially, a detailed description of the centrifugal pump model and the optimization system was provided. Subsequently, sensitivity analysis of key parameters was conducted through design of experiments (DOEs), identifying the primary factors influencing the pump performance. This research demonstrated that the blade wrap angle, as well as the leading and trailing vane exit angles of the front and back shrouds, are crucial factors affecting the performance of the centrifugal pump, with the blade wrap angle exerting a particularly significant impact on pump efficiency, contributing up to 83.6%. After optimization, the pump’s head increased by 1.29%, and the efficiency improved by 2.96%. The flow field of the optimized pump was significantly improved, with enhanced fluidity, achieving higher head and efficiency at a lower torque. Additionally, the pumping performance was augmented with an enhanced diffuser capacity in the pump volute, leading to increased exit pressure energy, while the turbulent kinetic energy and entropy production losses were significantly reduced. Under various operating conditions, the entropy production losses at the pump walls were all decreased, and the total mechanical energy within the impeller showed an increasing trend from the inlet to the outlet, resulting in lower energy consumption. In this paper, a reference is provided for further enhancing the hydraulic performance of centrifugal pumps in the future. Full article

The head, efficiency, and cavitation characteristics of centrifugal pumps are highly dependent on the velocity field in front of the impeller inlet. In multistage pumps, the velocity field in front of the second and each subsequent stage is determined by the shape (design) of the diffuser return guide vanes. This current work presents the results obtained by performing a numerical study using ANSYS CFX 14.0 to determine the impact of the shape (design) of diffuser return guide vanes on the head and coefficient of efficiency of one stage of a multistage centrifugal pump. Three RGVs with different Outlet angles are studied: ${\mathrm{\alpha }}_6$—original RGV with ${\mathrm{\alpha }}_6=90 \mathrm{deg}$, RGV1 with ${\mathrm{\alpha }}_6=110 \mathrm{deg}$ and RGV2 with ${\mathrm{\alpha }}_6=128 \mathrm{deg}$. The results obtained after performing CFD modeling indicate that with one of the studied RGVs, the pump stage head increases by nearly 20%, while the hydraulic coefficient of efficiency remains almost constant. Applying entropy production theory is used to determine the impact of the various components of entropy production on the total head loss in the studied pump stage. The impact of the Outlet angle of the RGV on the velocity field of the flow in front of the next impeller (stage) as well as the RGV head is also analyzed. The numerical results of the original RGV are compared with the experimental data obtained from large-scale studies of pumps performed at the Laboratory of Hydraulic Machines of the University “Angel Kanchev” of Ruse, Bulgaria. When using the modified RGVs, the head curve of the original pump can be obtained by operating at a lower speed or with a smaller impeller diameter. This may lead to an overall increase in the energy efficiency of the machine, which could be explored as a future task. Full article

Recent advancements in computational fluid dynamics (CFD) enable new and more complex analysis methods to be developed for early design stages. One such method is the isolated unsteady diffuser model, which seeks to reduce the computational cost of unsteady CFD when modeling diffusion systems in centrifugal compressors with vaned diffusers by isolating the diffuser from the computational domain and prescribing an unsteady and periodic inlet boundary condition. An initial iteration of this computational methodology was developed and validated for the Centrifugal Stage for Aerodynamic Research (CSTAR) at the High-Speed Compressor Laboratory at Purdue University. However, that work showed discrepancies in flow structure predictions between full-stage and isolated unsteady CFD models, and it also presented a narrow scope of only a single loading condition. Thus, this work addresses the need for improvement in the modeling fidelity. The original methodology was expanded by including a more accurate, non-uniform definition of turbulence at the diffuser inlet and modeling several loading conditions ranging from choke to surge. Results from isolated unsteady diffuser models with non-uniform turbulence modeling were compared with uniform turbulence isolated unsteady diffuser models and full-stage unsteady models at four loading conditions along a speedline. Flow structure predictions by the three methodologies were compared using 1D parameters and outlet total pressure and midspan velocity contours. The comparisons indicate a significant improvement in 1D parameter and flow structure predictions by the isolated unsteady diffuser models at all four loading conditions when including more accurate non-uniform turbulence, without a corresponding increase in computational cost. Additionally, both isolated diffuser methodologies accurately track trends in 3D flow structures along the speedline. Full article

Machine learning tools represent a key methodology for the shape optimization of complex geometries in the turbomachinery field. One of the current challenges is to redesign High-Pressure Turbine (HPT) stages to couple them with innovative combustion technologies. In fact, recent developments in the gas turbine field have led to the introduction of pioneering solutions such as Rotating Detonation Combustors (RDCs) aimed at improving the overall efficiency of the thermodynamic cycle at low overall pressure ratios. In this study, a HPT vane equipped with diffusive endwalls is optimized to allow for ingesting a high-subsonic flow ($Ma=0.6$) delivered by a RDC. The main purpose of this paper is to investigate the prediction ability of machine learning tools in case of multiple input parameters and different objective functions. Moreover, the model predictions are used to identify the optimal solutions in terms of vane efficiency and operating conditions. A new solution that combines optimal vane efficiency with target values for both the exit flow angle and the inlet Mach number is also presented. The impact of the newly designed geometrical features on the development of secondary flows is analyzed through numerical simulations. The optimized geometry achieved strong mitigation of the intensity of the secondary flows induced by the main flow separation from the diffusive endwalls. As a consequence, the overall vane aerodynamic efficiency increased with respect to the baseline design. Full article

The energy efficiency of water supply systems in high-rise residential buildings has become a significant concern for sustainable development in recent times. This work presents a numerical investigation on the influence of diffuser vane height on flow variation and hydraulic loss in the volute for a water supply centrifugal pump. Experiments and numerical simulations were conducted with four different vane height ratios. The numerical results were validated against experimental data. The hydraulic losses of different flow components were numerically evaluated at varying guide vane blade heights. The changes in flow patterns within the volute and the resulting discrepancies in hydraulic losses due to variations in the inlet flow conditions at different blade heights were studied. The findings indicate that the total pressure drop within the volute is affected significantly. Compared to traditional guide vanes, the reduced height vanes can reduce the hydraulic loss in the volute by nearly 75%. Once the vane height is reduced, the high-pressure gradient is improved, and the small-scale vortex vanishes. The influence area of the large-scale vortex in the volute outlet pipe decreases, leading to a weakening of the deflection of the main flow and ultimately resulting in reduced hydraulic loss. Full article

Vertical-axis wind turbines (VAWTs) are receiving more and more attention as they involve simple design, cope better with turbulence, and are insensitive to wind direction, which has a huge impact on their cost since a yaw mechanism is not needed. However, VAWTs still suffer from low conversion efficiency. As a result, tremendous efforts are being exerted to improve their efficiency, which mainly focus on two methods, regardless of whether the study is a CFD simulation, a field test, or a lab test experiment. An active approach involves modification of the rotor itself, such as the blade design, the angle, the trailing and leading edges, the inner blades, the chord thickness, the contra-rotating rotor, etc., while the second approach involves passive techniques where the flow is directed to optimally face the downwind rotor by mounting guiding vanes such as a diffuser or other shapes at the upwind position of the rotor. Among all the techniques undertaken, the counter-rotating wind turbine (CRWT) rotor technique seems to be the most effective, with an output comparable to that of horizontal-axis wind turbines (HAWTs), while the Savonius rotor has received more attention compared to other VAWT designs. Apart from technological issues, it has also been suggested that geographical issues, such as proper site siting of a wind turbine rotor at a particular location where a uniform flow can be guaranteed, are of paramount importance to ensure an effective conversion capacity of wind turbines. Thus, this study has successfully highlighted the latest improvements in augmentation methods and has established a solid foundation for future research aimed at improving the efficiency of VAWTs. Full article

The match of rotor and stator blades significantly affects the flow field structure and flow-induced pressure pulsation characteristics inside the pump. In order to study the effects of the rotor and stator matching mode on the complex flow field and pressure pulsation of a centrifugal pump with a vaned diffuser, this paper designs three different vaned diffusers (DY5, DY8 and DY9) and uses the DDES (Delayed Detached Eddy Simulation) numerical method combined with structured grids to simulate the unsteady flow phenomena of the model pump under rated conditions. The results show that, under different rotor and stator matching modes, the pressure pulsation spectrum is dominated by the blade passing frequency and its harmonics. The matching mode of the rotor and stator significantly affects the time–frequency domain characteristics of the pressure pulsation inside the pump, and it is observed that the pressure pulsation energy of vaned diffusers with more blades is significantly smaller than that of fewer-blade vaned diffusers in comparison to the energy of the pressure pulsation at the blade passing frequency and within the 10–1500 Hz frequency band. Combined with the distribution characteristics of the complex flow field inside the pump, it can be found that increasing the number of vaned diffuser blades can reduce the energy of flow-induced pressure pulsation, improve the distribution of high-energy vortices in the interaction zone and stabilize the flow inside the centrifugal pump effectively. Full article

In rotating detonation engines the turbine inlet conditions may be transonic with unprecedented unsteady fluctuations. To ensure an acceptable engine performance, the turbine passages must be suited to these conditions. This article focuses on designing and characterizing highly diffusive turbine vanes to operate at any inlet Mach number up to Mach 1. First, the effect of pressure loss on the starting limit is presented. Afterward, a multi-objective optimization with steady RANS simulations, including the endwall and 3D vane design is performed. Compared to previous research, significant reductions in pressure loss and stator-induced rotor forcing are obtained, with an extended operating range and preserving high flow turning. Finally, the influence of the inlet boundary layer thickness on the vane performance is evaluated, inducing remarkable increases in pressure loss and downstream pressure distortion. Employing an optimization with a thicker inlet boundary layer, specific endwall design recommendations are found, providing a notable improvement in both objective functions. Full article

High-pressure ratio centrifugal compressors’ diffusers face challenges from high-velocity, non-uniform flow at the impeller outlet, decreasing efficiency and stall margin. To address this, this paper presents a novel vaned diffuser passage design method that successfully improved the compressor’s performance. An optimization method using axisymmetric hub contours and NURBS curves was applied to modify the diffuser’s design. After optimization, centrifugal compressor peak efficiency increased by 0.78%, and stall margin expanded from 12.8% to 20.4%. Analysis at the peak efficiency point showed loss reduction mainly from decreased recirculation and mixing losses in the diffuser’s vaneless and semi-vaneless spaces. Furthermore, correlation analysis and Mach number distribution revealed that flow behavior at the diffuser’s leading edge significantly influences efficiency. Consequently, design principles emphasize satisfying specific Mach number distribution rules at the diffuser’s leading edge under certain inflow conditions for optimal performance. Full article

In the modern world, issues related to the use of alternative fuels are becoming increasingly pressing. These fuels offer the potential to achieve significantly improved environmental and technological performance. Currently, among such fuels, biodiesel, ammonia, LPG, and hydrogen are considered the most promising options. LPG and hydrogen exhibit a high Lower Heating Value (LHV) and have a relatively low environmental impact. This article investigates the combustion of hydrogen-LPG mixtures in a diffusion burner. The main parameters under study include the proportion of hydrogen in the fuel, equivalence ratio, and vane angle. The analyzed parameters encompass NOx and CO concentrations. The studies have demonstrated that the addition of hydrogen can reduce greenhouse gas emissions, as the combustion product is clean water. The primary focus of this research is the examination of combustion processes involving flow swirl systems and alternative fuels and their mixtures. The studies indicate that flame stabilization is significantly influenced by several factors. The first factor is the amount of hydrogen added to the fuel mixture. The second factor is the degree of mixing between the fuel and oxidizer, along with hydrogen. Lastly, the equivalence ratio plays a crucial role. As the studies have shown, the maximum stabilization for a speed of 5 m/s is achieved at an angle of 60° and a hydrogen fraction of 40%, resulting in φ_LBO = 0.9. This represents an 8.0% improvement in stabilization compared to the baseline mode, primarily due to the substantial proportion of hydrogen. An analysis of flame photographs reveals that as the twist angle increases, a recirculation zone becomes more apparent. Increasing the blade angle and incorporating hydrogen leads to a reduction in CO concentrations in the exhaust gases. The analysis indicates that increasing the hydrogen proportion to 50%, compared to the absence of hydrogen, results in a 30% decrease in CO concentration. In our case, for the option φ = 0.3 and blade angles of 60°, the reduction in CO concentration was 28.5%. From the authors’ perspective, the most optimal vane angle is 45°, along with a hydrogen fraction of 30–40%. With these parameters, it was possible to achieve concentrations of NOx = 17–25 ppm, φ_LBO = 0.66, and CO = 130–122 ppm. Full article