Large Eddy Simulation of Bubbly Ship Wakes

Abstract

Abstract : The presence of air bubbles in ship wakes and their dynamic interaction with the turbulent vortical flows create security problems by modifying the hydro-acoustic properties of ship navigation. This study concerns understanding and controlling the mechanisms which may lead to selective concentration of bubbles to form clusters or clouds and to predict their size distribution and motion. Numerical simulations were conducted using the Large Eddy Simulation (LES) technique in conjunction with a Lagrangian particle tracking (LPT) technique appropriate for dispersed two-phase turbulent flows. In order to cut down on the execution time of LES, the simulation for the flow around the ship model are not considered; instead the simulations started just after the ship where the inlet conditions are prescribed with the help of a newly developed Random Flow Generation (RFG) procedure, and to compute bubble distributions. Moreover, to improve turn-around time of the computations and allow LES of the developing wake in a larger domain, parallel simulation tools are developed and adopted in this study. The interaction of two-phases from the perspective of turbulence enhancement or damping in the near wake of ships seems to play an active role in determining bubble size and population. This, in turn, determines the phenomenon in the far wake which can be predicted using non-conventional techniques such as large eddy simulations. This is the focus area of the present study.