Session: 40-06: Turbine Secondary Flows and Interactions I

Paper Number: 153419

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

Cavitation instability in turbopump inducers is one of the major risks for launch vehicles. Unsteady loads on inducer blades and the turbopump rotor system can be caused by cavitation dynamics and lead to instability. For example, the cavitation dynamics can couple with the propellant feed system and result in POGO instability. Despite a large number of studies aimed at mitigating these risks, the fundamental understanding of the underlying mechanisms responsible for cavitation instability is still limited. 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. The criterion for rotating cavitation onset, governed by the position of the blade tip vortex, 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.

Presenting Author: Hiromitsu Kakudo Massachusetts Institute of Technology

Presenting Author Biography: Dr. Hiromitsu Kakudo is a researcher at Japan Aerospace Exploration Agency (JAXA), now working at MIT as a Visiting Engineer. His research topics are liquid rocket engine and turbomachinery. He has mainly focused on cryogenic turbopump’s elements such as cryogenic ball bearings and shaft seals, and cavitating inducers.

Authors:

Hiromitsu Kakudo Massachusetts Institute of Technology
James Wall Massachusetts Institute of Technology
Zoltan Spakovszky Massachusetts Institute of Technology