Numerical Investigation of Characteristics of Water-Exit Ventilated Cavity Collapse

The collapse of the ventilated cavitation occurring on a cylindrical vehicle during the water-exit is numerically researched. The numerical model employs the finite volume method to solve the multiphase Reynoldsaveraged Navier-Stokes(RNNS) equations and uses the volume of fluid(VOF) method to capture the free surface.A practical water wave environment that the vehicle usually encounters is reproduced in a numerical wave flume,so that the water wave’s effect on the cavity collapse flow regime is investigated. The main feature of the waterexit collapse of a ventilated cavity is studied under the wave-free condition. The result indicates that a collapsing ventilated cavity experiences two stages, in which the pattern of cavity evolution is different. In the early stage,the cavity undergoes a rapid shrinkage as a closed body. In the late stage, the cavity releases gas from the front due to the increase of the cavity pressure. The water wave effect is investigated at three typical wave phases: the wave crest, the wave trough and the wave node. Results show that when the vehicle is launched under the wave node, the cavity collapse regime remains fairly axisymmetric and is similar to the wave-free case. However, when the vehicle is launched under the wave crest and trough, the cavity evolution presents highly three-dimensional(3D) features. The results of predicted cavity size, pressure distributions and hydrodynamic forces at different wave phases show that the wave effect is relatively weak at the wave node but becomes apparent at the wave crest and trough.