LES Analysis of Horse-shoe Vortex around the Base of a Circular Cylinder by Means of a Lattice Boltzmann Method

The horse-shoe vortex appearing in front of the circular cylinder placed on the boundary layer was numerically investigated. The unsteady, three-dimensional feature of the flow field was captured by a lattice-Boltzmann method, where more than 300 million grids were used. The visualized instantaneous flow field indicated a complex vortex structure before and behind the cylinder. The spectrum analysis on the fluctuating pressure in these vortices indicated, however, there are only weak correlations between the horse-shoe vortex in front of the cylinder and the shed vortices in the wake. A strong down-ward flow in front of the cylinder was generated as a consequence of the horse-shoe vortex. The wall shear stress on the bottom wall was found to be maximum around the corner of the cylinder, as a consequence of the flow acceleration due to the down-ward flow which was related to the generation of the horse-shoe vortex