Wake behind circular cylinder excited by spanwise non-uniform disturbances

We experimentally investigated flow control of the wake behind a circular cylinder excited by temporal periodic disturbances with spanwise phase variations using DBD plasma actuators (PAs) array, motivated by suppressing development of large-scale wake vortices. PAs installed on the sides (+/- 90 deg from the forward stagnation point) were segmented in the spanwise direction, and the temporal phase differences, Φ = 0 or π, were given to adjacent electrodes. The width of the electrodes and gaps between them were chosen as 5 mm each. Experiment was conducted at Re_D = 8400 based on the cylinder diameter D = 23 mm, and the wake was visualized by stereo PIV. PAs were driven by 6kHz AC with voltage of 5-9 kV, and the range of St based on cylinder size was 1.0-2.2. In the case of Φ = π, a bundle of vortex lines which are selected to visualize the vortex structure formed in the following shear layer were shaped in a wavy pattern along spanwise direction with 180 degrees out of phase to the adjacent bundle. This structure, so called ‘chain-link fence structure’ was already found in planar free shear layer and planar jet, but it became evident to create it in the wake of circular cylinder in this study. The relation between the formation of the structure and drag forces will be clarified.