Investigation of the coupling mechanism between bent pipes and volute on the stall inception at the centrifugal compressor inlet

The rotating stall of a centrifugal compressor not only deteriorates its efficiency but also impacts the blade fatigue failure. The inlet total pressure distortion is generated by a 90° bent pipe placed upstream from the inlet. The volute causes the circumferential non-uniform static pressure distribution of the impeller outlet, and the impeller is under the inlet distortion and the non-uniform outlet distribution condition. Current research pays little attention to the stall inception location and its formation process under the coupling interaction between the bent pipe and volute. In this paper, two installation angles of the inlet bent pipe were compared concerning the stall inception process, including the 115° (M1) and the 295° (M2) models. The circumferential angle between the volute tongue and the elbow axial plane approaches a blade passage width in model M1, and model M2 has the opposite installation angle to M1. The model M1 inlet low total pressure region caused by the bent pipe, and the outlet high static pressure region induced by the volute tongue together affect the same impeller passage at the 115° location causing the leading edge spillover. The coupling effect of the Model M1 accelerates the process of stall. However, the low total pressure region for the model M2 is located at the circumferential 295° point, and the high static outlet pressure affects the 115° impellers, resulting in a different stall inception location and process compared to the model M1. The leading edge spillover first occurs at the 295° location because of inlet distortion, and the second spillover appears at the 115° location due to the reversed propagation of the outlet high pressure region induced by the volute tongue. Compared to model M1, the stall formation of model M2 is relatively slow. Meanwhile, because of the recirculation flow, the static temperature rises sharply and the axial velocity drops significantly at the spillover region during the stall process. These results indicate that the coupling interaction between the low total inlet pressure and the high outlet static pressure jointly determines the stall inception location and its process at the centrifugal compressor inlet.