The Use of High-Speed Photography in the Study of Cavitation

Abstract

Cavitation is caused by the reduction of pressure in liquids to approximately the vapour pressure. The formation of these cavitation bubbles causes loss of efficiency in hydraulic machines and there may be erosion damage to the surfaces when the bubbles collapse. High-speed photography, either by single-shot or multi-shot cameras, is one of the most useful tools for the study of cavitation. The various methods and techniques available are discussed. It is shown that, although speeds of the order of one million frames/second may be necessary to investigate the life history of a cavitation bubble, speeds of the order of 2,000 to 50,000 frames/second are, in general, sufficient, especially if used in conjunction with a synchronised flashlight of microsecond duration to improve definition.

A description is given of the camera and lighting techniques employed in the study of cavitation at M.E.R.L. A 35-mm. camera is used for still photographs, and a 35-mm. high-speed camera with a taking rate up to 8,000 frames/second for cine records. Both cameras are used in conjunction with synchronised 5-microsecond period electronic flashlights. High-speed photographs taken by these methods are given in the paper, including cavitation on a wedge-shaped diverter in water, on a cylinder in water, and in oil flowing through a piston valve; and the very small bubbles found at the inception of cavitation, the photograph being taken through a microscope.