Ventilated supercavitation around a moving body in a still fluid

Abstract

Present experimental study examines ventilated supercavity formation in an unbounded or free-surface bounded environment where the body is in motion and the fluid is at rest. The experiments were conducted in an open water tank where a high-speed towing system (max. 10m/s) is adopted to move an underwater axisymmetric ellipsoidal body with a certain speed. The body has a disk-type cavitator on its nose and compressed air is ventilated radially between the nose and the cavitator. Various steady-state supercavity formations are observed according to relevant Froude numbers, the air entrainment coefficients, and the cavitation numbers

twin-vortex supercavity (TV), reentrant-jet supercavity (RJ), partial supercavity with foamy cavity downstream (PSF), partial supercavity with shedding of continuous vortex rings downstream (PSV), double-layer supercavity (RJ inside & TV outside, TV inside & TV outside, RJ inside & RJ outside). Connected with this behavioral observation, the body-frontal-area based drag coefficient for a moving ellipsoidal body with a supercavity is measured to be on the order of 0.1 while that for a cavitator-free moving body without supercavity is on the order of 0.4. There have been few experimental studies on the ventilated supercavitation in an unbounded or open environment like the present experimental setting. We believe that our experimental study can provide both new and complimentary results which may be overlooked in many existing experimental studies in cavitation tunnels where the body is at rest and the fluid is in motion in a bounded or closed environment.