Large eddy simulation in complex geometric configurations using boundary body forces

A numerical method is presented that allows large eddy simulation (LES) of turbulent flows in complex geometric configurations with moving boundaries and that retains the advantages of solving the Navier-Stokes equations on fixed orthogonal grids. The boundary conditions are applied independently of the grid by assigning body forces over surfaces that need not coincide with coordinate lines. The use of orthogonal, nondeforming grids simplifies grid generation, facilitates the implementation of high-order, nondissipative discretization schemes, and minimizes the spatial and temporal variations in filter width that complicate unstructured deforming-grid LES. Dynamic subgrid-scale turbulence models are particularly appealing in combination with the body-force procedure because the dynamic model accounts automatically for the presence of solid walls without requiring damping functions. The method is validated by simulations of the turbulent flow in a motored axisymmetric piston-cylinder assembly for which detailed experimental measurements are available. Computed mean and rms velocity profiles show very good agreement with measured ensemble averages. The present numerical code runs on small, personal computer-like workstations. For a comparable level of accuracy, computational requirements (memory and CPU time) are at least a factor of 10 lower compared to published simulations for the same configuration obtained using an unstructured, boundary-fitted deforming-grid approach.