An experimental study of exit flow patterns in a multistage compressor in rotating stall
High-response pressure measurements of a high-speed, 10- stage, axial-flow compressor operating in rotating stall are analyzed. Procedures used to digitize analog voltages and calibrate pressure transducers are presented. From total and static pressures measured at the exit of the test compressor, stall cell Mach number distributions are calculated and used to study the effects of discharge throttle levels and variable vane changes on the 10th-stage rotating stall cells. Results indicate that significant transition zones exist between the reverse flow and peak Mach number of the stall cell cycle.
Since the axial Mach numbers of the stall cell cycle are constantly changing, the amount of leading and trailing edge transition zones and fully unstalled flow zones are not easily defined. A method is devised to approximate the different flow zone ranges and correlate them to in-stall pressure characteristic behavior of the 10th stage of the test compressor. Changes in the time-averaged pressure characteristics are found to correlate with changes in the rotating stall flow zones. A lower pressure coefficient appears to correspond to an increase in the ratio of trailing to leading edge transition zone size and the average transition zone size. Results also suggest that recovery hysteresis in the test compressor is characterized by reverse flow in the rotating stall cell.