On the Mechanism for Rotating Cavitation Onset in a Four-Bladed Rocket Engine Turbopump Inducer

Abstract Cavitation instabilities in liquid rocket engines can lead to turbopump performance degradation and catastrophic damage to engine components, and there is still a gap in understanding the underlying mechanisms governing the cavitation dynamics. The present study characterizes the different cavitation regimes of a four-bladed inducer using unsteady pressure and optical measurements, specifically the transition from tip vortex cavitation to alternate blade cavitation and rotating cavitation, depending on cavitation number. Cavitation compliance and mass flow gain factor, the two key parameters characterizing inducer dynamics and pumping system stability, are inferred from the measurements using a previously developed dynamic inducer model [1]. The criterion for rotating cavitation onset, governed by the position of the blade tip vortex [2], is validated via optical measurements. A first-principles-based model for the trajectory angle of the tip vortex cavitation is established and yields good agreement with experimental results. The paper demonstrates that the criterion for rotating cavitation onset is independent of inducer geometry and sets the stage for more generalized inducer design guidelines to address cavitation instability.