Dynamic mode characteristics of flow instabilities in a single-stage compressor under different throttling processes

Abstract

To investigate the influence of throttling processes on dynamic characteristics of compressor stability, the rotating stall development of National Aeronautics and Space Administration Stage 35 was simulated with full-annulus Unsteady Reynolds-Averaged Navier–Stokes under different throttling processes. The numerical methods were verified. By combining Dynamic Mode Decomposition and flow field evolution research, the flow structures and dynamic characteristics of “critical mass flow” under different throttling processes were deeply studied; the flow mechanism of flow instabilities under different throttling processes was explored. It is found that the “critical mass flow” corresponds to the beginning of a rapid decrease in mass flow, mainly characterized by shock forward movement and a larger range of spillage flow. Around “critical mass flow,” if the throttle is still tightening, it presents stall pattern 2; otherwise, it presents stall pattern 1. During the pre-stall, both patterns are dominated by tip clearance vortex (TCV)-shock interference. Stall inception disturbance is generated from TCV-shock interference; pattern 1 presents a single disturbance, while pattern 2 presents multiple disturbances. Subsequently, the TCV-shock interference gradually weakens. The single stall disturbance of pattern 1 gradually develops and stabilizes. The multiple stall disturbances in pattern 2 undergo processes including fusion and disappearance, ultimately developing into a single stall cell. During the stable stall, the throttling processes have no significant impact on the speed of the stall cell, and the flow in the un-stalled region is basically consistent with the speedline. However, the tighter the throttle is, the larger the stalled region, and the weaker the flow capacity of the un-stalled region.