A Rotating Stall Type Phenomenon Caused by Cavitation in LE-7A LH2 Turbopump

The cause of 350 Hz large-amplitude rotor vibration of the H-2A rocket's LE-7A fuel turbopump was investigated by wideband oscillating-pressure measurement. Measurement was successfully conducted by quartz-type pressure sensors in full-load liquid-hydrogen tests. The phase difference of pressure oscillations between two pressure measurement ports under conditions of pump cavitating operation revealed a phenomenon similar to rotating stall in turbomachinery which had not been previously observed. The rotating speed of a cell was 350 Hz, about a half the rotor speed. This phenomenon is different from rotating cavitation in which the cavitation pattern rotates around the periphery of an impeller faster than shaft rotating speed. Based on these findings, it was concluded that this phenomenon cased the large-amplitude 350 Hz vibration of the LE-7A fuel turbopump. Results of FFT analysis of measured oscillating pressure are presented.