Stability improvement without efficiency penalty of a transonic centrifugal compressor by casing treatment and impeller/diffuser coupling optimization

Abstract

Self-recirculation casing treatment (SRCT) is usually used to improve the flow stability of centrifugal compressors, while extra aerodynamic losses are often introduced. It is challenging to remove the efficiency penalty for the design of SRCT. In this study, a coupling optimization is implemented to redesign a transonic centrifugal compressor with an SRCT. Firstly, the physical design space is expanded to include the design parameters of both the SRCT and the impeller/diffuser. Secondly, data-mining techniques are used to explore and refine the expanded design space. Consequently, seven critical design parameters are quantitatively identified, and they generally present non-linear and trade-off correlations with the compressor performances. Then, the global optimization is carried out for the refined design space. As a result, significant improvements of the aerodynamic performances of the compressor are obtained. The efficiency penalty introduced by the SRCT is eliminated, and the stable flow range is maintained simultaneously. This is infeasible for the single redesign of the SRCT or the impeller/diffuser. The flow mechanisms of the coupling optimization are as follows. The recirculation flow rate of the SRCT is increased, and more low-energy fluid near the shroud is removed. The incidence angle and the leading-edge blade loading at high spanwise region of the impeller are reduced. The interaction between the tip leakage vortex and the inducer shock wave is delayed and weakened. The inlet mixing loss and the inlet radial distortion of the impeller are decreased. The friction loss is reduced and the flow separation is suppressed in the vaned diffuser.