Experimental investigation on ventilated cavity flow of a model ship

Abstract

A ventilated cavity model ship is investigated in a calm water towing tank under a moderate Froude number range. The gas ventilation rate required for cavity from early formation to complete coverage is explored, as well as the cavity morphology, closure modes, shedding features, and cavity growth characteristics. Several flow patterns of the cavity are classified, i.e., discrete foamy flow and initial coalescing cavity, corresponding to the formation stage; jet growth cavity(JGC), bifurcation growth cavity(BGC), meniscus growth cavity(MGC), and waterfall growth cavity(WGC), corresponding to the logarithmic growth stage; and bottle neck stable cavity, corresponding to the maturity stage. The shedding features of small periodic oscillation shedding, group rips evolution shedding, and wave pinch-off shedding are observed corresponding to JGC, BGC, and MGC and WGC, respectively. Three hypothetical mechanisms, rectangular jet dominant, pressure difference dominant, and wave pinch-off dominant, are proposed to be responsible for the formation of JGC, BGC and MGC, and WGC, respectively. A logarithmic mathematical model is related to cavity length and ventilation rate. The dependence of gas demand required to establish a complete coverage cavity on Froude number (0.37–1.10, ship length based) is more significant than Reynolds number (5.95 × 106–1.78 × 107, ship length based).