Novel Diagnostic Techniques for Identification of Inducer Cavitation Dynamics

Abstract: The cavitation dynamics of a rocket engine turbopump inducer was characterized via high-response unsteady pressure and velocity measurements combined with front- and side-view optical imaging. The data was processed using Traveling Wave Energy (TWE) analysis to determine the temporal evolution of frequency, spatial shape, and direction of rotation of the natural oscillatory modes of the flow field during cavitation transients. The test inducer, dubbed the MIT inducer, is representative of a low-pressure liquid oxygen pump (LPOP) inducer of modern design. All experiments were conducted in the Aerospace Corporation’s Cavitation Test Facility. The paper will also discuss a new approach to measuring fluctuating mass flow and velocity for potential use in forced response identification of the inducer transfer matrix relevant for POGO instability assessment. Previous work on the mechanism responsible for rotating cavitation suggests that rotating cavitation is caused by coupling of the cavities on adjacent blades during alternate blade cavitation. Due to the nearly tangential flow, the vortex lines from one of the non-cavitating blades wrap around the blade leading edge of the adjacent blade, which yields a drop in static pressure and cavity formation. The tip vortex interaction with the leading edge of the next blade leads to sheet cavity breakdown with periodic cavity growth and collapse. This creates the apparent super-synchronous rotation of the cavities. The measurements presented in this paper support these hypotheses.