Experimental investigation of critical air entrainment in ventilated cavitating flow for a forward facing model

Abstract

Ventilated supercavitation is a favorable method for skin friction reduction of underwater bodies, whereby a cavity is generated through artificial injection of air to cover the entire body. In the current study, several experiments are carried out to investigate ventilated supercavity behavior under different flow conditions. A closed-wall water tunnel and air injection system are provided to form ventilated supercavities around a model which was mounted in a forward facing setup. The present research concentrates on the formation and collapse processes of supercavities in order to determine the critical values of air entrainment coefficients which are important parameters for the ventilation demand of a high-speed supercavitating vehicle. Our experiments show that there are critical air entrainment coefficients in which the supercavity length suddenly increases or decreases, due to the change of closure mode between the re-entrant jet regime and twin vortex regime at the rear portion of the supercavity. The results reveal that the formation and collapse air entrainment coefficients vary with Froude number. Moreover, some pressure sensors are positioned in the model and are used to measure the pressure distribution inside the supercavity. The most novelty of our work is to present measurements of the supercavity pressure for a forward facing model, especially at closure region of the supercavity. The pressure measurements show that the pressure increases slightly along the test body surface and is accompanied by a sharp increase at the closure region of the supercavities.