A CRITICAL-EVALUATION OF NEAR-WALL 2-EQUATION MODELS AGAINST DIRECT NUMERICAL-SIMULATION DATA

Two-equation turbulence models with near-wall corrections are assessed by applying them to calculate plane Couette flow-a flow case where co nventional two-equation models and second-order closures fail to give a correct prediction of the spatial distribution of the turbulent kine tic energy-plane channel flow, and flat plate boundary-layer flow. The predictions of 10 near-wall two-equation models, including the k-tau and k-omega models and 5 recently developed asymptotically consistent near-wall k-epsilon models, are compared with data obtained from direc t numerical simulations at very low Reynolds numbers. It is found that models that are not asymptotically consistent are incapable of predic ting the spatial distribution of k correctly in Couette flows. Instead , they give a fairly uniform distribution of k across a substantial po rtion of the channel. Of all the models evaluated, the asymptotically consistent k-epsilon models are found to perform the best compard to d irect numerical simulation (DNS) data and experimental measurements. F ive of the ten models are further validated against DNS data of a back stop flow at low Reynolds number. Similar results as before are obtain ed. Therefore, the present results lend credence to the hypothesis tha t an internally consistent and asymptotically correct near-wall model is of crucial importance to the calculations of wall-bounded turbulent flows. (C) 1997 by Elsevier Science Inc.