Numerical Investigation of Diffuser Stall Inception in a Centrifugal Compressor with Fishtail Diffuser

Abstract

This paper presents diffuser stall inception in a centrifugal compressor with fishtail diffuser investigated by experimental and numerical analyses. The numerical simulation showed that the diffuser stall was the two-cell rotating stall originating from the low-speed region that occurred at opposing positions. When the mass flow rate was stable, the separation was observed on the suction side wall at the upstream of the diffuser bend and the secondary flow was observed at the downstream of the bend. Before the stall, the blockage increased due to the suction side boundary layer separation. Because of the separation extending to the throat, the mass flow rate on the throat decreased, leading to stall. The secondary flow crawled under the suction side separation at the bend. In near stall condition, the secondary flow that contributed to the suction side separation was developed at the bend. From these observations, it was concluded that the diffuser stall inception was caused by the suction side boundary layer separation due to the secondary flow development.