<p> Rising costs and volatility in aviation fuel and increased regulations resulting from climate change  concerns have driven gas turbine engine manufacturers to focus on reducing fuel consumption.  Implementing centrifugal compressors as the last stage in an axial engine architecture allows for  reduced core diameters and higher fuel efficiencies. However, a centrifugal compressor's  performance relies heavily on its stationary diffusion system. Furthermore, the highly unsteady  and turbulent flow field exhibited in the diffusion system often causes CFD models to fall short of  reality. Therefore, rapid validation is required to match the speed at which engineers can simulate  different diffuser designs utilizing CFD. One avenue for this is through the use of additive  manufacturing in centrifugal compressor experimental research. This study focused on implementing a new generation of the Centrifugal Stage for Aerodynamic  Research (CSTAR) at the Purdue Compressor Research Lab that utilizes an entirely additively  manufactured diffusion system. In addition, the new configuration was used to showcase the  benefits of additive manufacturing (AM) in evaluating diffusion components. Two diffusion  systems were manufactured and assessed. The Build 2 diffusion system introduced significant  modifications to the diffusion system compared to the Build 1 design. The modifications included changes to the diffuser vane geometry, endwall divergence, and increased deswirl pinch and vane  geometries. The Build 2 diffusion system showed performance reductions in total and static  pressure rise, flow range, and efficiencies. These results were primarily attributed to the changes  made to the Build 2 diffuser. The end wall divergence resulted in end wall separation that caused  increased losses. The changes to the diffuser vane resulted in increased throat blockage and lower  pressure rise and mass flow rate. In addition to the experimental portion of this study, a computational study was conducted to study  the design changes made to the Build 2 diffusion system. A speedline at 100% corrected rotational  speed was solved, and the results were compared to experimental data. The simulated data matched  the overall stage and diffusion system performance relatively well, but the internal flow fields of  the diffusion components, namely the diffuser, were not well predicted. This was attributed to  16 using the SST turbulence model over BSL EARSM. The BSL EARSM model more accurately  predicted the diffuser flow field to the SST model.  </p>

<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>