Explicit Filtering and Reconstruction Turbulence Modeling for Large-eddy Simulations of Field-scale Flows

Large-eddy simulation (LES) has become a widely-used method for computation of field-scale environmental flows; however, challenges remain in determining the optimal turbulence closure method. Recently, the concept of explicit filtering and reconstruction has become recognized as a means to obtain more accurate simulation results (Carati et al. 2001, Winckelmans et al. 2001, Stolz et al. 2001, Gullbrand and Chow 2003). In this paper we review these new methods and extend them to flow over a rough boundary at field scale. By partitioning the subfilter-scale total turbulent stress into resolved and unresolved components, it becomes clear that the resolved component can be reconstructed using a series expansion to approximate the inverse filter operation. The unresolved stress, i.e., subgrid-scale stress, must be modeled. We apply the dynamic reconstruction model (DRM), using reconstruction plus a dynamic eddy viscosity model and a near-wall enhanced stress model, to simulate an incompressible fluid flow in a channel over a rough boundary. Standard eddy viscosity closures fail to reproduce the expected logarithmic velocity profile when used alone. The DRM produces much improved results, yielding a logarithmic profile that extends over 10-15% of the boundary layer depth with accompanying nondimensional shear numbers close to unity.