Int. J. Turbomach. Propuls. Power, Volume 5, Issue 2 (June 2020) – 7 articles

Injection pattern of the oxidizer injected into the combustion chamber is a significant factor in evaluating the performance of a hybrid rocket. In the hybrid rocket combustion process, oxidizer flows over the solid fuel grain surface, leading to a turbulent diffusion boundary layer formation and the flame is established inside the boundary layer. The heat transfer from flame to the fuel surface leads to pyrolysis of the fuel. The heat fluxes, due to pyrolysis, block the heat transfer further to the fuel surface, thus reducing the fuel regression rate. An attempt has been made in this paper to design and study the effect of the multi-angle diverging injector on the enhancement of the fuel regression rate and combustion efficiency of the hybrid rocket. The designed injector was compared with a shower head injector i.e., axial injector. The fuels used were paraffin wax and polyvinyl chloride (PVC) with gaseous oxygen as oxidizer. The effect of formation of the re-circulation zone and flow velocity were studied numerically by a cold flow simulation using ANSYS-Fluent software. It has been observed that direct impingement of the multi-angle diverging injector produces velocity in three directions, leading to distortion of the boundary layer. An increase of 8% in the average fuel regression rate for PVC fuel grain and 36.14% for paraffin wax fuel grain was observed, as compared to the shower head injector for the same oxidizer mass flow rate. A combustion efficiency increase of 38% and 14% was also observed using multi-angle diverging injector for PVC and paraffin wax fuel grains, respectively. A reduction in sliver and uniform fuel consumption was also observed using the novel multi-angle diverging injector. Full article

Mechanically robust turbine design with respect to blade vibration is challenging when dealing with nozzle-ring fouling and wear. Especially for engines operating with heavy fuel oil (HFO), the nozzle rings of the turbocharger turbines are prone to severe degradation in terms of contamination with unburned fuel deposits. This contamination will lead to an increased excitation of blade resonances in comparison to the nominal design. Due to the statistical character of contamination, long-term monitoring of blade vibration amplitudes would be beneficial. In the harsh environment of HFO operation, however, conventional blade vibration measurement techniques, such as those using strain gauges or blade tip timing, cannot work reliably for a long period. Thus, the objective of this research is to develop a method that enables the monitoring of turbine blades using pulsation or vibration sensors installed on the stator side. Almost a dozen turbines, both radial and axial, have been examined in order to determine a proper measurement chain/position and analytical method. Even though the challenges specific to the turbocharger turbine application—that high-frequency (up to 50 kHz) acoustic radiation from turbine blades has to be detected by a sensor on the stator side—were demanding, in the course of the investigations several clear examples of turbine blades engine-order resonance detection were gathered. Finally, the proposed method has been tested successfully in a power plant for over one year. Full article

The paper presents a state-of-the-art review of turbine trailing edge flows, both from an experimental and numerical point of view. With the help of old and recent high-resolution time resolved data, the main advances in the understanding of the essential features of the unsteady wake flow are collected and homogenized. Attention is paid to the energy separation phenomenon occurring in turbine wakes, as well as to the effects of the aerodynamic parameters chiefly influencing the features of the vortex shedding. Achievements in terms of unsteady numerical simulations of turbine wake flow characterized by vigorous vortex shedding are also reviewed. Whenever possible the outcome of a detailed code-to-code and code-to-experiments validation process is presented and discussed, on account of the adopted numerical method and turbulence closure. Full article

A siren is a robust fast-valve that generates effective flow pulsations and powerful noise levels under well-controlled conditions. It operates under the inlet flow conditions of a gas turbine combustor. Its principle is based on a sonic air jet periodically sheared by a cogged wheel rotating at a given speed. It is used as an alternative to loudspeakers in combustion laboratories when the use of these is made difficult by aggressive flow conditions, such as hot air under pressure, possibly containing impurities. It is also a serious candidate as an effective flow actuator to be deployed on power gas turbine fleets. The authors have gathered more than twenty years of knowledge on siren technology. This pulsator was originally developed for research on thermoacoustics. By scanning through a given frequency range, one detects the acoustic resonance of specific parts of the combustor assembly, or possibly triggers a combustion instability during a sensitivity analysis of a flame to small perturbations. In 2010, Giuliani et al. developed a novel siren model with the capacity to vary the amplitude of pulsation independently from the frequency. In this contribution, the physics, the metrics, and the resulting parameters of the pulsator are discussed. Technical solutions are unveiled about visiting large frequency ranges (currently 6 kHz) and achieving elevated pressure fluctuations (150 dB SPL proven, possibly up to 155 dB SPL) with a compact device. A multimodal excitation is available with this technology, one idea being to dissipate the acoustic energy on nearby peaks. The contribution ends with a summary of the applications performed so far and the perspective of an industrial application. Full article

Current commercial and heavy-duty powertrains are geared towards emissions reduction. Energy recovery from exhaust gases has great potential, considering the mechanical work to be transferred back to the engine. For this purpose, an additional turbine can be implemented behind a turbocharger; this solution is called turbocompounding (TC). This paper considers the adaptation of turbine wheels and gearboxes of small turboshaft and turbojet engines into a two-stage TC system for a six-cylinder opposed-piston engine that is currently under development. The initial conditions are presented in the first section, while a comparison between small turboshaft and turbojet engines and their components for TC is presented in the second section. Based on the comparative study, a total number of 7 turbojet and 8 turboshaft engines were considered for the TC unit. Full article

In the side-chambers of radial turbomachinery, which are rotor–stator cavities, complex flow patterns develop that contribute substantially to axial thrust on the shaft and frictional torque on the rotor. Moreover, leakage flow through the side-chambers may occur in both centripetal and centrifugal directions which significantly influences rotor–stator cavity flow and has to be carefully taken into account in the design process: precise correlations quantifying the effects of rotor–stator cavity flow are needed to design reliable, highly efficient turbomachines. This paper presents an experimental investigation of centripetal leakage flow with and without pre-swirl in rotor–stator cavities through combining the experimental results of two test rigs: a hydraulic test rig covering the Reynolds number range of $4\times {10}^5\le Re\le 3\times {10}^6$ and a test rig for gaseous rotor–stator cavity flow operating at $2\times {10}^7\le Re\le 2\times {10}^8$ . This covers the operating ranges of hydraulic and thermal turbomachinery. In rotor–stator cavities, the Reynolds number $Re$ is defined as $Re=\mathsf{\Omega }\raisebox{1ex}{$b^2$}\!\left/ \!\raisebox{-1ex}{$\nu $}\right.$ with angular rotor velocity $\mathsf{\Omega }$ , rotor outer radius b and kinematic viscosity $\nu$ . The influence of circumferential Reynolds number, axial gap width and centripetal through-flow on the radial pressure distribution, axial thrust and frictional torque is presented, with the through-flow being characterised by its mass flow rate and swirl angle at the inlet. The results present a comprehensive insight into the flow in rotor–stator cavities with superposed centripetal through-flow and provide an extended database to aid the turbomachinery design process. Full article

This paper presents and discusses the recent developments on the Fast-Response Aerodynamic Pressure Probe (FRAPP) technology at the Laboratorio di Fluidodinamica delle Macchine (LFM) of the Politecnico di Milano. First, the different geometries developed and tested at LFM are presented and critically discussed: the paper refers to single-sensor or two-sensor probes applied as virtual 2D or 3D probes for phase-resolved measurements. The static calibration of the sensors inserted inside the head of the probes is discussed, also taking into account for the temperature field of application: in this context, a novel calibration procedure is discussed and the new manufacturing process is presented. The dynamic calibration is reconsidered in view of the 15-years’ experience, including the extension to probes operating at different temperature and pressure levels with respect to calibration. As for the probe aerodynamics, the calibration coefficients are discussed and the most reliable set here is evidenced. A novel procedure for the quantification of the measurement uncertainty, recently developed and based on the Montecarlo methodology, is introduced and discussed in the paper. Full article