THE FREESTREAM MATCHING CONDITION FOR STAGNATION POINT TURBULENT FLOWS - AN ALTERNATIVE FORMULATION

The problem of plane stagnation point flow with freestream turbulence is examined from a basic theoretical standpoint. It is argued that the singularity which arises in the standard K-epsilon model results from the use of an inconsistent freestream boundary condition. The inconsi stency lies in the implementation of a production-equals-dissipation e quilibrium hypothesis in conjunction with a freestream mean velocity f ield that corresponds to homogeneous plane strain-a turbulent flow for which the standard K-epsilon model does not predict such a simple equ ilibrium. The ad hoc adjustment that has been made in the constants of the epsilon-transport equation to eliminate this singularity is shown to be inconsistent for homogeneous plane-strain turbulence as well as other benchmark turbulent flows. An alternative means to eliminate th is singularity-without compromising model predictions in more basic tu rbulent flows-is proposed based on the incorporation of nonequilibrium vortex stretching effects in the turbulent dissipation rate equation.