(Sorry for the long text, hope someone will read and comment 😄 ) I started reading about LES few days ago, and here is what I understood so far (to be corrected): Physically : Eddies are present in the flow, larger eddies are the size of the geometry (~characteristic diameter let's say) and take their kinetic energy from the mean flow. Large eddies then "decompose" into smaller eddies by the cascade principle. When the eddies are finally small enough, they dissipate into heat. Physically, the loss into heat happen at all eddies size, but it is assumed that >90% of the transfer into heat happens at very small eddies only (not modeled by CFD) Numerically : The goal is to resolve the grid-size eddies, and model the sub-grid scales ones. However in LES models (Smagorinsky atleast, the only one I read properly), small eddies are supposed to be isotropic, and that is the reason why your mesh should be fine. If your mesh is not fine enough, the calculated dissipation will assume your eddies are isotropic, when they might not be in real life, and so your dissipation will be badly calculated > wrong results. Mesh size : the mesh size should be: - normal to the wall : y+ < 1, with smooth grid expansion - streamwise : 50 < x+ < 150 - spanwise : 15 < z+ < 40 Values depends on the literature, but basically it's around those values, even though cases were shown to give proper results with x+ and z+ ~1500.