Experiment on cavitation instability of inducer under wide-range operating conditions

To develop the rocket engine turbo-pump with a wide range of stable operation, the influence of inlet flow coefficient on the dynamic characteristics of a three-blade inducer is examined based on visualization experiment and analysis of corresponding pressure fluctuation characteristics. It is revealed that the inducer blade tip pressure fluctuation amplitude increases with the increase of the inlet flow coefficient, and increases first and then decreases with the decrease of the cavitation number. The amplitude of inducer blade tip pressure fluctuation drops further to the non-cavitating condition in the vicinity of cavitation breakdown. Rotating cavitation is observed at 90%-110% design inlet flow coefficient. Additionally, it is clarified that the occurrence range of rotating cavitation extends to high cavitation number at a lower inlet flow coefficient, leading to the problem of operation stability. At 70%-80% Q_d, where positive head-to-flow rate curve is caused by cavitation head breakdown, a sub-synchronous azimuthal instability of about 90% shaft frequency is identified as rotating choking, and an axial instability of about 70% shaft frequency as choked surge.