Eddy viscosity models for wakes and separated flows

The accuracy of eddy-viscosity-type models (EVM) in computing turbulent-flow parameters is investigated, comparing EVM predictions with experimental data and the predictions of differential-equation models. The flow at the trailing edge of a flat plate and the flow past a backward-facing step are computed by solving the 2D unsteady compressible Navier-Stokes equations at Mach 0.4 by a pseudotransient, time-split finite-element formulation; the EVM is based on that of Deiwert (1976). The results are presented graphically and discussed. It is found that the EVM describes most features of wake and separated flows satisfactorily, with the exception of the shear stress near the wall downstream from the reattachment (e.g., 0.014 EVM versus 0.011 experimental). This deficiency, however, is also characteristic of two-equation models such as the (k-epsilon) model.