Investigation of ship wakes using LES with various SGS models

Turbulence plays an important role in ship wake flows. Without the knowledge of turbulent intensities and length scale information it is virtually impossible to model and predict turbulence characteristics in complex flows, such as ship wake flows. Moreover, the behavior of ship wakes requires an understanding of the turbulence near a free surface. The present study will focus on identifying the contributions of various mechanisms, but primarily that of the free surface, to the process of turbulence generation and dissipation in the wake of a turning ship using the large eddy simulation (LES) technique. LES is applied in conjunction with a random flow generation (RFG) technique originally developed at West Virginia University to provide unsteady inflow boundary conditions. Some refinements are made to extend the capabilities of a readily available LES code in predicting turbulence, including among others, appropriate sub-grid scale (SGS) turbulence models. A modified zero equation SGS model is developed, to account for the free surface effects. Furthermore, a non-linear one equation model is developed and tested to represent the anisotropy of turbulence observed near a free surface. Finally, using LES the turbulence characteristics in the wake of a turning ship are studied and compared to that of a ship cruising on a straight track.