Visualization of the Trailing Vortices Using Cavitation Inception Bubbles

Abstract

It is assumed that cavitation bubbles in wakes of bodies are produced in the cores of vortices formed in the wakes. An attempt to estimate the pressures in the cores of vortices formed in the wakes of circular cylinders has been made by image processing of the high-speed photographs of incipient cavitation bubbles. The vortices were taken for Rankin's vortices. The tangential velocity distributions in the vortices were measured by visualization of vortices using contour extraction and measuring rotational angle for the images of cavitation inception bubbles. It was possible to obtain the tangential velocities of cores of vortices from the peak of the tangential velocity distribution. The pressure reductions in the vortices were obtained from the tangential velocities of the cores. The pressures of the centers in the cores of vortices were obtained by subtracting the pressure reductions in the vortices from ambient wall pressures. It is satisfactory to consider that the pressure reductions by vortices bring vapor pressure or under vapor pressure in the cores of vortices at cavitation inception caused by vortices.