Circulation Control of a Circular Cylinder using Discrete, 3-D Coanda Wall Jets

Controlled circulation over wings to effect significant lift increments has been realized by the Coanda effect of a nominally 2-D wall jet over a bluff trailing edge or the flap. The present wind tunnel investigation explores the utility of segmented Coanda actuation for generating streamwise and cross-stream loads using spanwise arrays of fluidically oscillating wall jets integrated into a 2-D cylinder model with specific emphasis on the interaction of the control jets with the cross flow and their effects on the near wake. It is shown that compared to a conventional 2-D wall jet, 3-D jets having the same momentum coefficient effect substantial improvements in attained lift increments without significant changes in induced drag. The effects of the 2- and 3-D wall jets on separation in adverse pressure gradient over the cylinder’s curved surface are investigated using stereo PIV measurements revealing differences in structural features of induced streamwise vorticity concentrations that alter the spanwise interactions with the cross flow and thereby suppress separation. The 3-D features of boundary layer entrainment, separation, and vorticity transport and interactions between adjacent jets are assessed using POD analysis of the instantaneous velocity data.