Characteristics of Stable Rotating Stall Cells in an Axial Compressor

Abstract

Flow field measurements of a high-speed axial compressor are presented during pre-stall and post-stall conditions. The paper provides an analysis of measurements from a circumferential array of unsteady shroud static pressure sensors during stall cell development. At low-speed, the stall cell approached a stable size in approximately two rotor revolutions. At higher speeds, the stall cell developed within a short amount of time after stall inception, but then fluctuated in circumferential extent as the compressor transiently approached a stable post-stall operating point. The size of the stall cell was found to be related to the annulus average flow coefficient. A discussion of Phase-Locked Average (PLA) statistics on flow field measurements during stable operation is also included. In conditions where rotating stall is present, flow field measurements can be Double Phase-Locked Averaged (DPLA) using a once-per-revolution (1/Rev) pulse and the period of the stall cell. The DPLA method provides greater detail and understanding into the structure of the stall cell. DPLA data indicated that a stalled compressor annulus can be considered to contained three main regions: over-pressurized passages, stalled passages, and recovering passages. Within the over-pressured region, rotor passages exhibited increased blade loading and pressure ratio compared to pre-stall values.

Observations of the Growth and Decay of Stall Cells during Stall and Surge in an Axial Compressor

“…These results show it is purely the poststall throttling point in conjunction with the system dynamics that determine whether surge will grow from rotating stall. For a further analysis of the rotating stall case see Hickman and Morris [19].…”

“…Instantaneous shroud and rotor exit unsteady pressure contours are presented during transient events in order to better understand the process of stall inception and stall development. A comparison between stall and surge events is also given to describe how the onset of surge occurs [15].…”