Numerical Investigation of Low Reynolds Number Effects on Energy Loss Inside Centrifugal Compressor with Different Inlet Conditions

As the Reynolds number of centrifugal compressors decreases with increasing flight altitude of the light aeroengines, the associated performance degradation has been a key limitation in the energy conversion efficiency of propulsion system. In this study, the performance and internal flow field at different Reynolds numbers of a subsonic and a transonic centrifugal compressor are numerically simulated to discuss the effect of the Reynolds number on energy loss inside compressors with different inlet condition. The loss coefficient is introduced to normalize the energy loss at different operating points, and the local dissipation coefficient is introduced as the integration weight function to establish a general method for distinguishing different types and sources of energy loss inside compressors. The similarities and differences in the flow mechanisms of performance degradation of these two compressors at low Reynolds number are clarified. The results show that the low Reynolds number has a strong impact on both subsonic and transonic centrifugal compressors, and the performance degradation comes from both the impeller and diffuser. More energy loss from velocity gradient due to thicker boundary layer at low Reynold numbers is the commonality of the centrifugal compressor with different inlet condition. The difference in secondary flow structure is the main reason why these two impellers have different loss coefficient and outlet flow field at different Reynolds numbers. Although the increase diffuser loss of these two compressors at low Reynolds numbers comes from the blockage, the flow structures are different, which is strongly related to the static pressure recovery coefficient.