Numerical Investigation of Premature Stall in a Non-Tip-Loaded Rotor Caused by Circumferential Groove Casing Treatment

Abstract

Casing treatment design and application typically focus on improving stall margin while minimizing efficiency penalty for tip-loaded rotors. When successful casing treatment configurations are found, it often is assumed that their beneficial effects will occur across the whole operating line. Our investigation revealed the effects of casing treatment on the compressor stability in circumstances such as an off-design situation in which the rotor tip becomes unloaded; that is, in which stall originates elsewhere than at the rotor tip. A widely used circumferential groove casing treatment configuration was installed in a non-tip-loaded rotor, and computational fluid dynamics was employed to simulate the internal flow. The numerical results showed that the stall was induced by a detached vortex located at 90% span near the trailing edge, and the grooves near the blade leading edge significantly negatively affected the stall margin. Based on a computational fluid dynamics analysis, it was found that a special flow structure consisting of a spanwise tornadolike separation vortex and a stream of radial underflow establishes a connection between the grooves and the stall-critical detached vortex away from the tip. Our research explained the stall mechanism and showed that the casing treatment does not always have a beneficial or neutral effect on compressor stall margin. On the contrary, it significantly can decrease the stability for non-tip-loaded rotors. Thus for conditions in which the rotor tip becomes unloaded, potential harmful effects of casing treatment on the stability margin need to be considered.