A Numerical Study on Rotating Stall Inception in an Axial Compressor

Abstract

A series of numerical study was conducted to analyze stall inception process and to find the mechanism of rotating stall in a subsonic axial compressor. The compressor used in this study showed different flow behaviors depending on the inlet boundary layer thickness at the near stall condition. The hub-corner-separation grew to become a full-span separation for the thick inlet boundary layer as the load was increased. The initial disturbance was initiated in these separations on suction surfaces, and then it was transferred to the tip region. This disturbance grew to be an attached stall cell, which adheres on a blade surface and rotates at the same speed as the rotor. Once the attached stall cell reached a critical size, it moved along the blade row and became the rotating stall. On the other hand, it was reduced to be indistinguishable from the rotor wake and other large separation occurred near the casing for the thin boundary layer. The different boundary layer affects the stall cell’s size and the initial disturbance causing the rotating stall. The stall cell grew large with the increasing boundary layer, causing large performance drop during stall developing process. Influence of the number of flow passages on the rotating stall was also investigated by comparing the results obtained using four and eight flow passages. The stall inception process was similar in both cases, while the number of stall cells was different because of the size of the computational domain. Based these results, the minimum number of flow passages was suggested for rotating stall in a subsonic axial compressor.