Active Control of a Cylinder Wake Using Surface Plasma

Abstract

An experimental investigation has been undertaken using high-speed Particle Image Velocimetry to study the possibility of controlling the global flow field in the near wake of a circular cylinder at Re = 6,500.Surface plasma actuators were mounted at strategic locations around the cylinder (both fore and aft of the separation point) and used for flow control by producing a body force close to the wall.It was found that the plasma can significantly alter the vortex shedding in the wake of the cylinder, with effectiveness depending upon the actuator location and forcing frequency.The most dramatic effects were observed when the plasma was located very close to the natural laminar separation point.Here, amplification of the shedding was observed when the plasma was excited at the natural vortex shedding frequency (St f ≈ 0.2; St K = 0.206).This was accompanied by periodic flow reattachment to at least the rearward stagnation point.At higher forcing frequency (St f ≥ 0.8), the plasma completely suppressed the vortex shedding process which lead to a short and narrow wake, reduced turbulence intensity, and 60% reduction in the wake momentum thickness.At still higher frequency (St f ≥ 2.0; St SL = 1.7), only the shear layers were excited and the vortex street remained unaltered.