A study of turbulent vortices in the near wake of a cylinder

Abstract

Turbulent vortices in the wake of a circular cylinder have been examined in some detail following their detection by a method based on vorticity concentration and circulation. The experimental data were obtained at a Reynolds number Re = 5600 (based on the free-stream velocity and cylinder diameter) with an array of eight X-wires aligned in the plane of mean shear. Distributions of conditionally averaged vorticity and circumferential velocity within vortices are in reasonable agreement with those inferred from an Oseen vortex. The conditionally averaged streamwise velocity distribution through the vortex centre has a maximum at the centre, implying a vortex convection velocity greater than the local mean velocity. An Oseen vortex model reproduces the measured mean velocity and Reynolds stresses reasonably well. Results are also given for the streamwise variations of vorticity concentration, circulation and size of the vortices.