LOCAL GRID REFINEMENT IN LARGE-EDDY SIMULATIONS

A method for performing nested-grid calculations with a Large-Eddy Sim ulation (LES) code is described. The grid consists of a coarse mesh an d a fine mesh which overlaps the coarse in some region. A standard fin ite-volume method is used on both meshes. By means of grid communicati on, the velocity and pressure at both meshes are matched. To check tha t large eddies which are already resolved on the coarse grid are not a ffected by the nesting procedure, a simple two-dimensional mixing laye r is simulated. Several simulations of this flow have been carried out with a different number of grid points on the nested grid. It is foun d that, without much extra computational effort, the grid-nesting impr oves the turbulent statistics with respect to the results found on the coarse mesh. This improvement occurs first of all in the region where grid refinement is applied, but better results are also found on the coarse mesh outside the grid-refinement region. Furthermore, it is sho wn that the large-scale structures in this flow are not influenced by the boundary between the coarse and fine grid.