Introduction

Cavitation is defined as the formation of the vapor phase in a liquid due to the reduction of pressure to some critical value. The term cavitation can imply anything from the initial formation of bubbles (inception) to large-scale, attached cavities (supercavitation).  Cavitation can be distinguished from boiling in the sense that the former is induced by the lowering of hydrodynamic pressure, whereas the latter is induced by the raising of vapor pressure to some value in excess of the hydrodynamic pressure by raising temperature.

Any device handling liquids is subject to cavitation. Negative effects of cavitation include performance degradation in turbomachinery, hydroturbines and propulsion systems, noise and vibration and cavitation erosion.Useful applications of cavitation applications include ultrasonic cleaning, the homogenization of milk.Various chemical processes are enhanced by cavitation, such as coagulation, formation of suspensions and degassing of liquids. Cavitation can be used to increase heat and mass transfer in liquids, to promote crystallization and to enhance various sonochemical reactions such as polymerization and polymer degradation. Biomedical applications include the removal of kidney stones and automated drug delivery to patients. Important new applications in the pollution control area are also of interest. 

The St. Anthony Falls Laboratory has a long history of research activity in this field as well as extensive engineering experience in various applications. Most of our research is conducted in an interactive experimental/numerical/analytical approach. Fundamental research includes cavitation inception studies, super-cavitating and ventilated hydrofoil theory, drag reduction through super- or partial cavitation and microbubbles, hydroelastic phenomena, effect of cavitation on fluid transients, vortex cavitation, sheet/cloud cavitation, cavitation induced lift oscillations, effects on fluid transients cavitation erosion, and acoustics of bubbly flows, and many other related topics. The laboratory pioneered the development of cavitation nuclei measurement. At the same time, related efforts in the development of 3D, unsteady flow computational models was applied to sophisticated computer codes for calculating cavitating flow in complex geometry such as a large hydraulic turbine. As progress was made in computational fluid dynamics, the emphasis of this research has shifted from exclusively experimental and analytical studies to the use of an interactive experimental/numerical approach.