Behaviour of nonlinear two-equation turbulence models at the free-stream edges of turbulent flows

The behaviour of two-equation turbulence models at the outer edges of turbulent flows is studied in this paper. The focus is on nonlinear models with simple scalar-diffusivity gradient-diffusion model for turbulent transport. Conditions to obtain physically correct smooth solutions at the edge are presented and discussed. A constraint is derived for the diffusion model coefficient for turbulent kinetic energy to guarantee smooth solutions also when nonlinear constitutive models are employed. Finally, the analysis is extended to a case of a generalized gradient-diffusion model.