Visual Observations of Cavitation in Rocket Turbopump Inducer

Abstract

During the development of a liquid oxygen turbopump for the LE-7 engine of the H-II rocket, super-synchronous shaft vibrations (1.0-1.3ω) in the inducer were often observed. From the research of the vibration performance of the inducer, it was concluded that such vibrations were caused by the rotating cavitation in the inducer and it was also shown that the moderately increased diameter of the pump inlet was most effective to suppress such vibrations. To investigate those unstable phenomena in the inducer in detail, suction performance test of the inducer using a cavitation tunnel were conducted. From the results of the high-speed photograph analyzer and of the spectrum analysis of the shaft vibration, three types of unstable cavitation modes, rotating cavitation, steady asymmetric cavitation and low cycle oscillation were observed. In this paper, the visual observation and its analysis results of unstable cavitation oscillation were reported in detail.