RIGOROUS MODELING OF DISSIPATION-RATE EQUATION USING DIRECT SIMULATIONS

With the aid of direct numerical simulation (DNS) data, we have constr ucted near-wall modeling of the dissipation-rate equation for a kappa- epsilon turbulence model. All the budget terms in the exact epsilon-eq uation are incorporated in the modeled epsilon-equation, and both term -to-term and overall comparisons of model predictions with the DNS dat a are performed. It is found that the wall region should be partitione d into at least two regions so as to reflect different mechanisms of t he generation processes in the dissipation of turbulent kinetic energy . Pressure diffusions in the kappa- and epsilon-equations are found to be equally important and thus should be modeled. Comparisons of the r esultant kappa-epsilon model with the DNS data of channel and boundary layer flows with and without pressure gradients show close agreement of various turbulent quantities. In particular, near-wall behavior of epsilon is reproduced with the present model very well.