Investigation of the wake of low aspect ratio cylinders by tomographic PIV

Abstract

The wakes of wall mounted circular cylinders of very low aspect ratio have been investigated in a wind tunnel. Besides planar PIV, also high resolution tomographic PIV was used to capture the flow phenomena downstream of the cylinder. By changing the velocity U_inf and the cylinder height h at a constant aspect ratio h/D, a wide database of different flow conditions was obtained. The resulting relative height of the boundary layer thickness was between h/delta=0.6 and h/delta=2.5, while the Reynolds number based on the length l between leading edge and cylinder centre Re_l was between Re_l=57,000 and Re_l=188,000. A pair of counter-rotating vortices was found in the wake of the cylinder. The rotation sense is such, that in the center of the wake a positive vertical velocity component results. Also horseshoe vortices were found next to these trailing vortices. The relative height of the incoming boundary layer has a large impact on the development, strength and dissipation of the vortex system.