Wavelet multi-resolution analysis on vortical structures of a dune wake based on large eddy simulation

The three-dimensional orthogonal wavelet multi-resolution technique was applied to analyze flow structures of various scales behind a dune model The three-dimensional dune wake flow was evaluated by using large eddy simulation (LES) at a Reynolds number of 5530. The instantaneous velocity and vorticity were decomposed into the large-, intermediate- and relatively small-scale components by the wavelet multi-resolution technique. The coherent structure are visualized by Q-criterion. It is found that the rollers and horse-shoe structure in the separation bubble are mainly contributed from large-scale structures, furthermore, some horse-shoe structures can be clearly identified by intermediate-scale structures, the coherent structures are the combined effect of large-scale and intermediate-scale structures. The velocity and vorticity of large-scale structure dominate the dune wake flow and the vorticity concentration makes main contribution, and the intermediate-scale as well as the relatively small-scale ones tends to become more active as the flow flows downstream.