Book Description

Cavitation is a serious concern in liquid fueled launch vehicle propulsion systems which operate at high speeds to meet the engine thrust requirements. There are several types of cavitation instabilities, but of concern in this work is one-dimensional planar oscillations known as cavitation surge. In a launch vehicle the resulting dynamic behavior can lead to thrust oscillations and couple with the structures of the launch vehicle, leading to POGO instability (named after the POGO jumping stick) that can cause catastrophic failure. This thesis introduces a foundation for a method of forced response characterization of cavitating inducers and presents for the first time, damping ratio and natural frequency measurements of surge dynamics using a forced response system identification approach over different cavitation numbers. Cavitation dynamics have been experimentally characterized in the past via transmission matrices. In this work, dynamic pressure and velocity measurements were used to form transfer functions of the cavitating inducer. Experimental guidelines were developed to increase the stiffness of the structure to isolate fluid perturbations, condition the flow downstream of the inducer using honeycomb and wire mesh elements which increased the signal-to-noise ratio of the velocity measurements by 28%, and signal processing techniques to average and smooth the measurements.