Visualization of Rotating Cavitation Oscillation Mechanism in a Turbopump Inducer

An experimental investigation has been conducted on rotating cavitation in a turbopump inducer. Previous research suggested that incidence angle variation leads to rotating cavitation. This study, using particle image velocimetry (PIV) method, provides the first measurement of the incidence angle distribution near the tip region of an inducer blade's leading edge with and without rotating cavitation. Without rotating cavitation, the incidence angle near the leading edge of the following blade is positive. Under rotating cavitation, the tip leakage vortex cavitation regions on the blades become uneven, forming large and small tip leakage vortex cavitation regions. A large tip leakage vortex cavitation on the leading blade increases the axial and absolute tangential velocities near the following blade's leading edge. Thus, the incidence angle on the following blade becomes negative, suppressing tip leakage vortex cavitation. Conversely, a small tip leakage vortex cavitation on the leading blade increases the incidence angle and promotes tip leakage vortex cavitation on the following blade. Due to such suppression and promotion mechanisms, the tip leakage vortex cavitation region on each blade oscillates in sequence, seemingly but not actually propagating in the forward direction. High-speed camera flow visualization has been used to confirm the same oscillation mechanism of rotating cavitation.