Measurements in High Void Fraction Bubbly Wakes Created by Ventilated Supercavitation

Abstract

A study of ventilated supercavitation in the reentrant jet regime has been carried out in the highspeed water tunnel at St. Anthony Falls Laboratory as the hydrodynamics part of an interdisciplinary study on stability and control of highspeed cavityrunning bodies. The work is aimed at understanding the interaction between a ventilated supercavity and its turbulent bubbly wake, with the goal to provide the information needed for the development of control algorithms. Particle image velocimetry (PIV) measurements in highvoid fraction bubbly wakes created by the collapse of ventilated supercavities are reported. Bubble velocity fields are obtained and are shown to submit to the same high Reynolds number similarity scaling as the singlephase turbulent axisymmetric wake. A grayscale technique to measure local average void fraction is outlined. Results of a timeresolved PIV experiment at 2000 Hz, using an adaptive masking scheme based on a sliding intensity threshold filter, are also presented.