On Streamwise Vorticity Dynamics in a Wake

Abstract

The streamwise vortices are detected experimentally in the wake behind a circular cylinder in Reynolds number 5 thousand on the top of Kármán vortex street dynamics. The stereo time-resolved PIV method has been used to detect the wake and streamwise vortices. The wake is moving periodically in spanwise direction due to Kármán vortex-street, consisting of vortices oriented in the cylinder axis direction. Both dynamical structures in the wake, the streamwise velocity component deficit and the streamwise vorticity concentration, are moving periodically in transversal direction with the same frequency, the vorticity concentration is shifted by a quarter of period before the velocity deficit in the shedding process. The streamwise vorticity is the most intense if the wake is in dead-end positions.