LES of Solid-Wall/Free-Surface Juncture Flow

The interaction of turbulent structures with a free--surface is a very interesting topic in the frame of naval hydrodynamics. In fact, most CFD codes for naval applications exploit models developed, calibrated and tested for aeronautic applications. These models do not take into account the effects of the moving boundary, which strongly influences the structures near the juncture between a solid wall and a free--surface~cite{Stern}, or in the wake of a ship hull. As an example for the second type of flow, the case of a turbulent flow in an open channel has been studied. The numerical method adopted is a second order accurate both in space and time finite difference scheme. Large eddy simulation has been carried out with a Smagorinsky sub grid scale model~cite{Smag}. The most relevant effect of the moving boundary on the turbulent structures is a redistribution of the velocity fluctuations normal to the free-surface to the parallel components; the global effect is turbulence with two dimensional features near the free--surface. Moreover, during the decay of the turbulence is possible to observe a thickening of this two dimensional layer. In the paper the flow at the juncture between solid--wall and a free--surface will be analysed, with particular attention to the effects on the main turbulent characteristics of the flow.