A discontinuous subgrid eddy viscosity method for the time-dependent Navier-Stokes equations

In this paper we provide an error analysis of a subgrid scale eddy viscosity method using discontinuous polynomial approximations for the numerical solution of the incompressible Navier-Stokes equations. Optimal continuous in time error estimates of the velocity are derived. The analysis is completed with some error estimates for two fully discrete schemes, which are first and second order in time, respectively

Discontinuous subgrid formulations for transport problems

In this paper we develop two discontinuous Galerkin formulations within the framework of the two-scale subgrid method for solving advection–diffusion-reaction equations. We reformulate, using broken spaces, the nonlinear subgrid scale (NSGS) finite element model in which a nonlinear eddy viscosity term is introduced only to the subgrid scales of a finite element mesh. Here, two new subgrid formulations are built by introducing subgrid stabilized terms either at the element level or on the edges by means of the residual of the approximated resolved scale solution inside each element and the jump of the subgrid solution across interelement edges. The amount of subgrid viscosity is scaled by the resolved scale solution at the element level, yielding a self adaptive method so that no additional stabilization parameter is required. Numerical experiments are conducted in order to demonstrate the behavior of the proposed methodology in comparison with some discontinuous Galerkin methods.Indisponível

INTERIOR PENALTY DISCONTINUOUS GALERKIN METHODS WITH IMPLICIT TIME-INTEGRATION TECHNIQUES FOR NONLINEAR PARABOLIC EQUATIONS

Abstract. We prove existence and numerical stability of numerical solutions of three fully discrete interior penalty discontinuous Galerkin (IPDG) methods for solving nonlinear parabolic equations. Under some appropriate regularity conditions, we give the l 2 (H 1 ) and l ∞ (L 2 ) error estimates of the fully discrete symmetric interior penalty discontinuous Galerkin (SIPG) scheme with the implicit θ-schemes in time, which include backward Euler and Crank-Nicolson finite difference approximations. Our estimates are optimal with respect to the mesh size h. The theoretical results are confirmed by some numerical experiments

Helicity and Physical Fidelity in Turbulence Modeling

This thesis is a study of physical fidelity in turbulence modeling. We first consider conservation laws in several popular turbulence models and find that of the Leray, Leray-deconvolution, Bardina and Stolz-Adams approximate deconvolution model (ADM), all but the Bardina model conserve a model energy. Only the ADM conserves a model helicity. Since the ADM conserves a model energy and helicity, we then investigate a joint helicity-energy spectrum in the ADM. We find that up to a filter-dependent length scale, the ADM cascades energy and helicity jointly in the same manner as the Navier-Stokes equations.We also investigate helicity treatment in discretizations of turbulence models. For inviscid, periodic flow, we implement energy conserving discretizations of the ADM, Leray, and Leray-deconvolution models as well as the Navier-Stokes equations (NSE) and observe helicity treatments. We find that of none of the models conserve helicity (or model helicity) in the discretizations. Since the Leray-deconvolution model of turbulence is newly developed, our implementation is new and thus we analyze the trapezoidal Galerkin scheme that we implement and compare it to the usual Leray model.Lastly, we develop an energy and helicity conserving trapezoidal Galerkin scheme for the Navier-Stokes equations. We prove conservation properties for the scheme, stability, and show the scheme does not lose asymptotic accuracy compared to the usual trapezoidal Galerkin scheme. We also present numerical experiments that compare the energy and helicity conserving scheme to more typical schemes

HP Primal Discontinuous Galerkin Finite Element Methods for Two-Phase Flow in Porous Media

The understanding and modeling of multiphase flow has been a challenging research problem for many years. Among the important applications of the two-phase flow problem are simulation of the oil recovery and environmental protection. The two-phase flow problem in porous media is mathematically modeled by a nonlinear system of coupled partial differential equations that express the conservation laws of mass and momentum. In general, these equations can only be solved by the use of numerical methods.The research in the thesis mainly focuses on the numerical simulation and analysis of different models of incompressible two-phase flow in porous media using primal Discontinuous Galerkin (DG) finite element methods.First, in our work we derive sharp computable lower bounds of the penalty parametersfor stable and convergent symmetric interior penalty Galerkin methods (SIPG) applied to the elliptic problem. In particular, we obtain the explicit dependence of the coercivity constants with respect to the polynomial degrees and the angles of the mesh elements. These bounds play an important role in the derivation of the stability bounds for the SIPG method applied to the the two-phase flow problem. Next, we consider three different implicit pressure-saturation formulations for two-phase flow. We study both h- and p-versions, i.e. convergence is obtained by either refining the mesh or by increasing the polynomial degree. We develop numerical analysis for one of the pressure-saturation formulations. Numerical tests which confirm our theoretical results are presented. Some validation of the proposed schemes, comparison between numerical solutions which are obtained by different schemes and numerical simulations of benchmark problems also given