Numerical Analysis of a Variational Multiscale Method for Turbulence

This thesis is concerned with one of the most promising approaches to the numerical simulation of turbulent flows, the subgrid eddy viscosity models. We analyze both continuous and discontinuous finite element approximation of the new subgrid eddy viscosity model introduced in [43], [45], [44].First, we present a new subgrid eddy viscosity model introduced in a variationally consistent manner and acting only on the small scales of the fluid flow. We give complete convergence of themethod. We show convergence of the semi-discrete finite element approximation of the model and give error estimates of the velocity and pressure. In order to establish robustness of themethod with respect to Reynolds number, we consider the Oseen problem. We present the error is uniformly bounded with respect to the Reynolds number.Second, we establish the connection of the new eddy viscosity model with another stabilization technique, called VariationalMultiscale Method (VMM) of Hughes et.al. [35]. We then show the advantages of the method over VMM. The new approach defines mean by elliptic projection and this definition leads to nonzerofluctuations across element interfaces.Third, we provide a careful numerical assessment of a new VMM. We present how this model can be implemented in finite element procedures. We focus on herein error estimates of the model andcomparison to classical approaches. We then establish that the numerical experiments support the theoretical expectations.Finally, we present a discontinuous finite element approximation of subgrid eddy viscosity model. We derive semi-discrete and fullydiscrete error estimations for the velocity