Session Cb - Turbulence Simulation.
ORAL session, Sunday, November 23
302, Moscone Center
Large-eddy simulation at high Reynolds numbers is only practical if near-wall regions are modelled to provide suitable boundary conditions for the core flow, allowing the grid there to be specified in a Reynolds number-independent manner. Results are presented for wall model tests in separated flow on a flat plate subject to an adverse pressure gradient and in flow over a backward-facing step. The boundary conditions can take two forms: 1) wall stress conditions applied at the wall, and 2) velocity conditions applied off of the wall. Preliminary results show that it is more difficult to employ the latter conditions successfully; and even when the boundary conditions are sufficiently accurate, unresolved subgrid-scale stresses on the coarse near-wall grid also must be modelled accurately to provide a consistent description of both mass and momentum fluxes near the walls. This is currently beyond the capability of standard subgrid-scale models used in large-eddy simulation, which are based on assumptions of isotropic turbulence and resolved energy-containing scales of motion.