Stability Enhancement in Aeroengine Centrifugal Compressors Using Diffuser Recirculation Channels
Abstract
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. 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.
Degree
M.Sc.
Advisors
Key, Purdue University.
Subject Area
Aerospace engineering|Design|Energy|Fluid mechanics|Industrial engineering|Mechanics
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