A Preliminary Study of the Effect of the Free Surface on a Three-dimensional Cavity Produced by a Circular Disk

Abstract

The influence of the free surface on the cavitation associated with bodies operating at shallow submergences has long been of interest because of the practical use for such information. The performance of hydrofoil boats is very much dependent on the submergence below the water surface of the hydrofoils, for example. Because of the extreme complexity introduced by the consideration of boundaries of any sort, most theories relating the parameters associated with cavitation are developed for a fluid of "infinite" extent. The task of determining the effects of the boundaries for such a cavitating flow problem then becomes one of experimentation. Such an experiment was performed to determine the free surface effects on a supercavitating, flat plate hydrofoil in two-dimensional flow p:: However, most real flow situations are three dimensional, and the present experiment is a preliminary study to determine the effects of the free surface on the geometry of a ventilated cavity in such a flow. Specifically, the variation of the length of a cavity due to submergence is studied. The cavity is produced by a sharp- edged, circular disk normal to the flow. Figures la and lb show this cavity at two different ventilation numbers. This experiment was planned as a preliminary study to determine the general trend and order of magnitude of the free surface effects, For this reason, the results are presented with the preliminary data reduced to the pertinent dimensionless parameters, uncorrected for tunnel blockage and model scale effects, if any.

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