A direct Navier-Stockes solver for turbulent flows over round steps

Kurzfassung

Direct Numerical Simulations (DNS) provide an increasing data source to improve our understanding of turbulent flows. Such DNS are especially required (together with generic experiments) to support flow physical modeling od separated, two- and three-dimensional vortex flows. In perspective to improve the prediction of such flows (either by new turbulence models or Large Eddy Simulations (LES) data fields are required which resolve turbulence and unsteady separated flow features. This is still a challenging task. However, a fully conservative, second order accurate, boundary correction method for Cartesian grids has been developed and implemented in an existing direct Navier-Stokes (NS) solver. For the case of a round backward facing channel step, laminar flow results generated with the proposed method agree well with those calculated on curvilinear, colocated grids. A Direct Numerical Simulation (DNS) of the turbulent flow in a minimal channel domain is performed for a Reynolds number based on friction velocity and channel height of ReT=265 for an efficiency analysis. Additionally the turbulent flows in a channel and a round backward facing channel step are calculated by means of DNS. The former simulation provides inflow conditions for the latter. The upstream Reynolds is ReT=360. Good agreement is obtained comparing statistically averaged variables of the turbulent channel flow with those of Kim et al. [3]. A mean recirculation zone, with mean separation/reattachment points being located 2.0/7.5 step heights downstream the step entrance, is computed in the DNS through the round backward facing channel step. Instantaneous and statistical flow variables are presented. They give an impression of the complex flow dynamics in the free shear layer, the recirculation and reattachment regions