Air bearing radial turbo (also called centrifugal) compressors prevail in most mobile fuel cell air supply applications due to the small size and weight, the high efficiency and the oil- and maintenance free operation. An important aspect in mobile fuel cell applications is the vibration resistance of all system components, including the compressor, with vibration requirements up to 20 g in automotive applications. This paper gives the background of the air bearing vibration characteristics, depicting the dependencies of vibration resistance on inlet conditions and operating points. The critical operating conditions concerning vibration resistance are identified, and it is outlined how vibration requirements can be included in the design process of an air bearing turbo compressor. A visualization of vibration resistance in the commonly used compressor map is presented, allowing the fuel cell system integrator to take qualified decisions for the mechanical integration of the compressor concerning vibrations.

<p>The purpose of this research was to determine what components of a complex centrifugal  compression system inlet needed to be modelled to accurately predict the swirl and total pressure  distortions at the compressor face. Two computational models were developed. A full-fidelity case  where all the inlet geometry was modelled and a reduced model where a small portion of the inlet  was considered. Both the numerical cases were compared with experimental data from a research  compressor rig developed by Honeywell Aerospace. The test apparatus was designed with a  modular inlet system to develop swirl distortion patterns. The modular inlet system utilized  transposable baffles within the radial-to-axial section of the inlet and blockage plates of varying  sizes and geometries at the inlet to this section.  Discerning the dominant inlet component that dictates distortion behavior at the compressor  face would allow the reduced modelling of inlet components for compression systems and would  allow coupling with more tortuous systems. Furthermore, it would reduce the design iteration and  simulation time of the inlet systems. Several investigations utilizing a reduced model only  considering a radial-to-axial inlet are available in literature, but no comprehensive justification has  been presented as to the impact this has on the distortion behavior.   Experimental surveys of flow conditions just upstream of the inducer of the centrifugal  compressor were conducted at several operating conditions. The highest and lowest mass flow  rates of these operating points were simulated using ANSYS CFX 2020R1 for both the  computational models. Multiple inlet configurations were simulated to test the robustness of the  reduced model in comparison to the full fidelity. The numerical simulations highlighted  shortcomings of the instrumentation used to characterize the experimental flow field at the inducer,  particularly with respect to total pressure distortion. Furthermore, transient pressure data were  measured in experiment and indicated unsteady fluctuations in the inlet that would not be captured  by steady computational fluid dynamic simulations. These data matched locations of disagreement  with swirl distortion behavior at high mass flow rates. This suggested that transient vortex  movement occured at the aerodynamic interface plane in certain configurations.   The total pressure distortion metrics between the two models were remarkably comparable.  Furthermore, the simplified model accurately predicted the mixing losses associated with the  blockage plates at the inlet to the radial-to-axial inlet using a simple inlet extension. Swirl  18  distortion was dictated by the radial-to-axial inlet. The reduced model data trends were comparable  with experiment for both the baffle and blocker plate configurations. The swirl intensities for all  configurations were comparable between the two models. The reduced model swirl directivity  trends matched those of experiment. The most notable deviations between the full-fidelity model  and the reduced model were observed with swirl directivity numerics. </p>

No description available.

<p dir="ltr">As aircraft engine manufacturers continue to embark on their pursuit of higher-efficiency, lower-emissions gas turbines, a prevailing theme in the industry has been the increase of the engine bypass ratio. As the optimization space for engine bypass ratios trends towards smaller and smaller engine core sizes, the feasibility of centrifugal compressors as the final stage in an axial-centrifugal compressor becomes apparent due to their performance advantages at smaller scales.</p><p dir="ltr">This study performed an investigation into the aerodynamics of a stationary diffusion system intended for use with a final stage aeroengine centrifugal compressor using experimental and numerical techniques. Experimental work was performed at the Purdue Compressor Research Lab at Purdue University’s Maurice J. Zucrow Laboratories. Data were collected from several iterations of rapidly prototyped, additively manufactured diffuser and deswirl parts with internal instrumentation features. Furthermore, computational work on the stage was conducted using the Ansys Turbosystem.</p><p dir="ltr">The goal of this research is to identify trends in stationary diffusion system designs and the geometric features that cause them. Furthermore, the ability of steady computational fluid dynamics methods to predict these changes was evaluated using two turbulence models to produce a simulation of the compressor flow field. When used in conjunction with one another, the efficient use of computational methods to identify an optimal design and rapid prototyping to validate it leads to the determination of the best diffusion system design at a lower cost and time requirement than what is otherwise currently possible.</p><p dir="ltr">The different geometries which were tested identified the negative effects of spanwise vane contouring on the diffuser performance and the ability of endwall divergence to augment the pressure recovery performance of a design at the expense of increased losses. A full understanding of the effect of each design parameter is enabled by iterative inclusion or exclusion of certain design parameters. Furthermore, the use of computational fluid dynamics showed that the BSLEARSM turbulence model performs reasonably well in predicting the build-to-build performance trends. However, neither the BSLEARSM nor the SST turbulence model were able to accurately identify performance trends for the deswirl. For this reason, additional work is warranted to identify an optimal set of parameters to characterize the high axial and meridional turning present in this component.</p>

This work will be focused on issue of a jet engine. The thesis will be divided into search retrieval part and computational part. In the search retrieval part it will focus on different configurations of jet engines as well as areas of their use. The main part of the thesis will however focus on a calculations where a turbine, compressor and an exhaust nozzle will be designed in order to give a thrust of approximately 1kN. Next step will be determination of an engine charcteristic that will give us a preview on how the engine performance will look like in off-design modes.

<p>The objective of this research was to develop stability enhancing design features for aeroengine centrifugal compressors. The motivation for this research is based on climate change and fuel-efficiency concerns, which call for improvements in achievable pressure ratios and surge margins. Specifically, this research aimed to develop diffuser recirculation channels and provide more insight into their design space. These channels are passive casing treatments in the diffuser and have been successfully demonstrated to improve stage surge margin. Diffuser recirculation channels are secondary flow paths that connect an opening near the diffuser inlet to one further down in the passage. Flow is recirculated by relieving the static pressure differential between the two openings. The basic design concept of these features is to add blockage upstream of the diffuser inlet, reducing the amount of diffusion in the vaneless space. In addition, channel geometries can be optimized to specifically target adverse flow properties, such as high incidence on the diffuser vane leading edge.</p> <p><br></p> <p>This design development was purely computational and served as the first approach to implementation of these features in a future generation of the Centrifugal Stage for Aerodynamic Research (CSTAR) at the Purdue Compressor Research Lab. Design development consisted of a computational design study, which quantified the effects of changing diffuser recirculation channel geometries on stage stability and performance metrics. Moreover, the CFD model for this future configuration of CSTAR was created and served as the baseline comparison for design iterations. The design study was comprised of controlled variation of channel geometry parameters and iterative solving of those cases in unsteady full stage single passage CFD models. Further design optimization studies were completed on specific down-selected recirculation channel geometry configurations. In total, 16 unsteady CFD cases with varied geometry configurations and 43 steady models were solved. Once a final optimized design was confirmed, a pressure characteristic at 100 % corrected design speed was generated. Compared to the baseline speed line, the implementation of diffuser recirculation channels resulted in a more gradual numerical surge and apparent numerical surge margin enhancement. Furthermore, the variation in incidence at the diffuser vane leading edge near the shroud was significantly reduced with diffuser recirculation. For the baseline compressor, incidence grew by about 70 degrees from the design aerodynamic loading to numerical surge at that location. However, flow stabilization due to diffuser 16 recirculation resulted in a change of approximately 2 degrees through that range. In conclusion, a first approach design recommendation for diffuser recirculation channels is CSTAR was generated through computational studies. Using this recommendation, diffusers with this recirculation channel design can be manufactured and tested for experimental concept validation.  </p>