EFFECTIVE VISCOSITY IN THE SIMULATION OF SPATIALLY EVOLVING SHEAR FLOWS WITH MONOTONIC FCT MODELS

The global numerical diffusion of a model for the low-Mach-number simulation of free mixing layers is investigated. The numerical model solves the inviscid time-dependent conservation equations for mass, momentum, and energy for ideal gases. The equations are solved using an explicit Flux-Corrected Transport (FCT) algorithm, directional timestep-splitting techniques on structured grids, and appropriate inflow and outflow boundary conditions. Effective measurement of the numerical diffusion of the model in uniform grids is performed by comparison of the laminar spread of the simulated mixing layers with that predicted by boundary layer theory. The results show that the residual numerical diffusion of the FCT model can emulate physical viscosity for laminar shear flows at moderately high Reynolds numbers. The global numerical diffusion is not very sensitive to changes in free-stream velocity ratio and can be reduced in a predictable way by refining the grid spacing. © 1992.