THE INTERACTION OF BACKGROUND OCEAN AIR BUBBLES WITH A SURFACE SHIP

A two-fluid model suitable for the calculation of the two-phase flow f ield around a naval surface ship is presented. This model couples the Reynolds-averaged Navier-Stokes (RANS) equations with equations for th e evolution of the gas-phase momentum, volume fraction and bubble numb er density, thereby allowing the multidimensional calculation of the t wo-phase flow for monodisperse variable size bubbles. The bubble field modifies the liquid solution through changes in the liquid mass and m omentum conservation equations. The model is applied to the case of th e scavenging of wind-induced sea-background bubbles by an unpropelled US Navy frigate under non-zero Froude number boundary conditions at th e free surface. This is an important test case, because it can be simu lated experimentally with a model-scale ship in a towing tank. A signi ficant, modification of the background bubble field is predicted in th e wake of the ship, where bubble depletion occurs along with a reducti on in the bubble size due to dissolution. This effect is due to latera l phase distribution phenomena and the generation of an upwelling plum e in the near wake that brings smaller bubbles up to the surface. (C) 1998 John Wiley & Sons, Ltd.