A study has been carried out to determine various aspects of the flow physics of a supercavitating vehicle at the Saint Anthony Falls Laboratory (SAFL). For the experimental work presented here, artificial supercavitation behind a sharp-edged disk was investigated for various model configurations. Results regarding supercavity shape, closure, and ventilation requirements versus Froude number are presented. Conducting experiments in water tunnels introduces blockage effects that are not present in nature. As a result, effects related to flow choking must also be considered. Two methods for computing ventilated cavitation number were compared, the first based on direct measurement of pressure and velocity, and the second technique based on measured cavity geometry and the use of previous numerical results. The results obtained are similar in character to previously reported data, but differ in measured numerical values. An attempt is made to correlate results from water tunnel experiments, where blockage has a significant effect, to an unbounded open flow. Supercavitation parameters, especially the minimum obtainable cavitation number are strongly affected by tunnel blockage.

A ventilated supercavity consists of a large, gas-filled bubble enveloped around an underwater vehicle that allows for significant drag reduction and increases in vehicle speed. Previous studies at the Saint Anthony Falls Laboratory (SAFL) focused on the behavior of ventilated supercavities in steady horizontal flows. In open waters, vehicles can encounter unsteady flows, especially when traveling near the surface, under waves. In supercavitation technology, it is critical that the vehicle remains within the cavity while traveling through water to avoid unwanted planing forces. A study has been carried out in the high-speed water tunnel to investigate the effects of unsteady flow on axisymmetric supercavities. An attempt is made to duplicate sea states seen in open waters. In an effort to track cavity dimensions throughout a wave cycle, an automated cavity-tracking script has been developed. Using a high-speed camera and the proper software, it is possible to synchronize cavity dimensions with pressure measurements taken inside the cavity. Results regarding supercavity appearance, cavitation parameters, and their relation to sea state conditions are presented. It was found that flow unsteadiness caused a decrease in the overall length of the supercavity while having only a minimal effect on the maximum diameter. The supercavity volume varied with cavitation number, and a possible relationship between the two was explored.

A study has been carried out at the Saint Anthony Falls Laboratory (SAFL) to investigate various aspects of the flow physics of a supercavitating vehicle. For the experimental work presented here, artificial supercavitation behind a sharp-edged disk was investigated for various model configurations. Results regarding supercavity shape, closure, and ventilation requirements versus Froude number are presented. Conducting experiments in water tunnels introduces blockage effects that are not present in nature. As a result, effects related to flow choking are also discussed. Various methods for computing ventilated cavitation number, including direct measurement of pressure, Laser Doppler Velocimetry, and use of previous numerical results, were compared. Results obtained are similar in character to previous results from various authors, but differ significantly in measured values. Supercavitation parameters, especially the minimum obtainable cavitation number are strongly affected by tunnel blockage.

An experimental study of air supply to bottom cavities stabilized within a recess under a horizontal surface has been carried out in a specially designed water tunnel. The air supply necessary for creating and maintaining an air cavity in steady and gust flows has been determined over a wide range of speed. Flux-free ventilated cavitation at low flow speeds has been observed. Stable multiwave cavity forms at subcritical values of Froude number were also observed. It was found that the cross-sectional area of the air supply ducting has a substantial effect on the air demand. Air supply scaling laws were deduced and verified with the experimental data obtained.

Small-scale water tunnel experiments of the phenomenon of supercavitation can be carried out broadly using two different kinds of experimental models-in the first model (forward facing model, or FFM), the incoming flow first interacts with the cavitator at front, which is connected to the strut through a ventilation pipe. The second model could have the strut and the ventilation pipe preceding the cavitator (backward facing model, or BFM). This is the continuation of a water tunnel study of the effects of unsteady flows on axisymmetric supercavities. In this study, the unwanted effect of test model configuration on supercavity shape in periodic flows was explored through a comparison of FFM and BFM models. In our experiments, it was found that periodic gust flows have only a minimal effect on the maximum diameter and the cavity length can be shortened above a certain vertical velocity of periodic flows. These findings appear to be robust regardless of the model configuration.

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