APPLICATION OF NON-LINEAR EDDY-VISCOSITY AND DIFFERENTIAL STRESS CLOSURES TO SEPARATED FLOW

Non-linear eddy-viscosity models and second-moment closure are examined, both theoretically and by comparison with 2-d and 3-d test cases featuring separation from mildly curved surfaces. It is found that, whereas non-linear stress-strain relations improve the prediction of normal-stress anisotropy, the mean flow dynamics are primarily influenced by the shear stress and, in particular, by the use of a strain-dependent linear coefficient. The advantages of second-moment closure are most apparent in fully 3-d flows, where several stress components are important. Determination of the turbulent length scale remains a crucial element in the performance of models in non-equilibrium flows.