Flow Arounds a Surface-Mounted Finite Cylinder: A Challenging case for LES

Paper in proceeding, 2008

Results of large eddy simulation of a flow around a cylinder with a finite aspect ratio (length/diameter) of 6 placed on a ground plane is presented. The Reynolds number based on the inlet velocity and the cylinder diameter is 20000. The boundary layer thickness at the position of the cylinder is approximately 7 % of the cylinder's diameter. In addition to the comparison of the time-averaged results with existing experimental data, the instantaneous flow was investigated. The fine mesh LES predicted the vortex shedding frequency in agreement with the experimental observations. Several important flow mechanisms are predicted and explained such as: the downwash of coherent structures from the region above the free end into the near wake or the formation of the alternate vortices in the far wake. Instantaneous flow structures around the cylinder such as horseshoe vortex, Kelvin Helmholtz and hairpin vortices are identified and their influence on the cylinder and the resulting aerodynamic forces is explained.