Investigation of stall process flow field in transonic centrifugal compressor with volute

Abstract

Owing to the asymmetric structure of the volute, the internal flow field in a centrifugal compressor is circumferentially non-uniform. Previous studies have paid little attention to whether the circumferentially non-uniform flow field has an influence on the circumferential position of stall inception under transonic inlet conditions. In this study, the performance of the centrifugal compressor and static pressure distribution around the casing wall are obtained by means of an experimental method. Thereafter, the experimental results are compared with the time-averaged results of unsteady simulations, and the stall process with shock waves is obtained. The results demonstrate that, in the presence of shock waves, the volute tongue (VT) determines the stall inception circumferential position. Owing to the asymmetric structure of the volute, the positions, strengths, and shapes of shock waves exhibit significant differences in varying blade passages. The VT induces the high static pressure region in a blade passage; the shock wave in the corresponding blade passage is much closer to the impeller inlet than the other blade passages; and the forward velocity of the shock wave in the stall process is significantly larger. Furthermore, leading edge spillage, which represents the stall inception, will first occur in this passage. The reason for these phenomena is that the high static pressure region can increase the static pressure at the blade passage outlet position, which compels the shock wave to move closer to the impeller inlet; therefore, stall inception first occurs in this passage. In the stall inception process, the shock wave in the blade passage, located in the low static pressure region, is not constantly moving to the impeller inlet; the shock wave moving direction also changes, and the shock wave moves downstream during a certain period. The tip leakage flow (TLF) trajectory in different blade passages differs significantly. Tip leakage vortex (TLV) breakdown first occurs in the blade passage that is most influenced by the VT.