Evaluation of subgrid-scale models in large-eddy simulation of flow past a two-dimensional block

Large-eddy simulations (LES) of flow past a two-dimensional (2D) block are performed to test the accuracy of four subgrid-scale (SGS) models in simulating the flow past a bluff body. An immersed boundary method (IBM) is developed to model the boundaries of the 2D block on the Cartesian grid of the simulation. The SGS models that are tested include (a) the Smagorinsky model, (b) the Lagrangian dynamic model, (c) the Lagrangian scale-dependent dynamic model, and (d) the modulated gradient model. In order to test the sensitivity of the results to grid resolution, simulations were performed with four different resolutions such that n_xxn_y= 16x20, 13x16, 10x12 and 6x8, where n_x and n_y are the number of grids across the block in the streamwise and vertical directions, respectively. The simulation results are compared with data from a wind-tunnel experiment. The modulated gradient model shows the best overall agreement with the experimental results among the four SGS models. Both the recirculation pattern and the vertical wind profiles are accurately reproduced by the modulated gradient model. Moreover, grid independent results are obtained in the simulations with that model using the two finest grid resolutions. Besides the modulated gradient model, the Lagrangian scale-dependent dynamic model is also able to reproduce the general flow patterns, but with relatively larger discrepancies in the prediction of the reattachment position and the recirculation center location. Finally, rather poor performance of the Smagorinsky model and the Lagrangian dynamic model is observed, which major differences between the simulated and the model flow statistics are found.