Energy contents and vortex dynamics in Mode-C transition of wired-cylinder wake

The 3D transition of the ¿ow behind a circular cylinder with a near-wake wire disturbance has been investigated experimentally. The ¿ow is oriented horizontally and the wire is positioned in the upper half of the wake. We performed ¿ow visualization and particle image velocimetry experiments to investigate the in¿uence of the wire on various properties of the ¿ow, such as the dynamics of the spanwise structures. Experiments were performed in the Reynolds number range of Re = 165–300. It is shown that in Mode-C transition of the wired cylinder wake, some part of the streamwise vorticity content of the upper von Karman vortices located at the perturbed side, is transferred to the secondary vortices. This vorticity transfer results in upper von Karman vortices which are weaker than the lower ones. The analysis of the discrete energy content of the wake supports this analysis by showing that the energy intensity at von Karman vortex shedding frequency f0 at the perturbed side of the wake is less than the energy intensity in the lower half. This leads to conclusion that the excess energy is transferred to the subharmonic frequency f1˜ f0/2.