Direct and large-eddy simulation of turbulent wall-bounded flows : further development of a parallel solver, improvement of multiscale subgrid models and investigation of vortex pairs in ground effect

This thesis is devoted to the numerical simulation of turbulent wall-bounded flows. Their accurate prediction is still challenging because of the nature of turbulence which is characterized by a very broad range of time and length scales. Therefore, fully resolved simulations of turbulent flows, called Direct Numerical Simulations (DNS), are unaffordable for practical applications but are an important research tool, since they provide a detailed insight into the physics of turbulence at moderate Reynolds numbers. In this thesis, direct simulations are used to study the interaction of a vortex pair with a wall and, more specifically, the development of instabilities which eventually lead to the turbulent decay of the system. That study is part of an important research effort devoted to aircraft wake vortices. The Reynolds number of the DNS is however much lower than that of aircraft wake vortices. This calls for investigations at higher Reynolds numbers using the Large-Eddy Simulation (LES) technique, which consists in simulating as small turbulent structures as the grid allows while modeling the effect of the unresolved scales using a subgrid-scale model. Performing LES of wake vortices in ground effect requires a subgrid-scale model that can handle both vortical flows and wall-bounded flows. The second part of this thesis deals with the development of such models. The proposed approach is based on the Regularized Variational Multiscale (RVM) model which is known to handle properly vortical flows thanks to its good spectral behavior. It is however shown in this thesis that the existing RVM model is not suitable for wall-bounded flows. New wall-adapting multiscale models are here obtained by using wall-adapting viscosity scalings in the regularized multiscale formalism. These models are successfully assessed in a turbulent channel flow and in a more complex test case consisting in a turbulent half channel with blowing and suction, in order to generate a non-uniform pressure gradient in the streamwise direction.(FSA 3) -- UCL, 200