DES of turbulent flow over wall-mounted obstacles using wall functions

An adaptive wall function is employed in Detached-Eddy Simulation (DES), a hybrid Reynolds-averaged Navier-Stokes (RANS) - Large Eddy Simulation (LES) model, of turbulent flow past two wall-mounted cubic obstacles in tandem at a Reynolds number Re = 22,000 based on the bulk velocity and the obstacle height. Numerical results are compared with previously published DES solutions obtained on wall integration grids and the experimental measurements of Martinuzzi and Havel (2000). The result shows that wallfunction approach in DES allows reasonable reproduction of coherent vortical structures massively separated from the wall-mounted obstacles to be achieved on wall function grids which require just the half of grid nodes of wall resolving grids. The numerical solutions computed by wall function computations reveal energetic unsteady flow fields with complex coherent vortical structures separated from obstacle edges, whose accuracy is better than those obtained by the unsteady RANS computations on the wall integration grid. Wall function solutions appear to be comparable to the wall-resolving DES solutions in most regions except at the junction of obstacle and the bottom wall where the flow is dominated by the horseshoe vortex with intense unsteadiness. The result confirms that DES with wall function approximation can reasonably resolves geometry-induced unsteady three-dimensional turbulent motions.