Ventilated supercavitation around a moving body in a still fluid

This experimental study examines ventilated supercavity formation in a free-surface bounded environment where a body is in motion and the fluid is at rest. For a given torpedo-shaped body and water depth (H), depending on the cavitator diameter (d$_{\mathrm{c}})$ and the submergence depth (h$_{\mathrm{s}})$, four different cases are investigated according to the blockage ratio (B$=$d$_{\mathrm{c}}$/d$_{\mathrm{h}}$, where d$_{\mathrm{h}}$ is the hydraulic diameter) and the dimensionless submergence depth (h*$=$h$_{\mathrm{s}}$/H). Cases 1--4 are no cavitator in fully submerged (B$=$0, h*$=$0.5), small blockage in fully submerged (B$=$15{\%}, h*$=$0.5), small blockage in shallowly submerged (B$=$1.5{\%}, h*$=$0.17) and large blockage in fully submerged (B$=$3{\%}, h*$=$0.5) cases. In case 1, no supercavitation is observed and only a bubbly flow (B) and a foamy cavity (FC) are observed. In cases 2 and 3, a twin-vortex supercavity (TV), a reentrant-jet supercavity (RJ), a half-supercavity with foamy cavity downstream (HSF), B and FC are observed. In case 4, a half-supercavity with a ring-type vortex shedding downstream (HSV), double-layer supercavities (RJ inside and TV outside (RJTV), TV inside and TV outside (TVTV), RJ inside and RJ outside (RJRJ)), B, FC and TV are observed. The body-frontal-area-based drag coefficient for a moving torpedo-shaped body with a supercavity is measured to be approximately 0.11 while that for a cavitator-free moving body without a supercavity is approximately 0.4.