Oscillatory control of separation at high Reynolds numbers

An experiment conducted in a pressurized, cryogenic wind tunnel demonstrate s that unsteady flow control using oscillatory blowing (with essentially ze ro mass flux) can effectively delay Row separation and reattach separated R ow on an airfoil at chord Reynolds numbers as high as 38 X 10(6), Oscillato ry blowing at frequencies that generate one to three vortices over the cont rolled region at all times are effective over the entire Reynolds number ra nge, in accordance with previous low-Reynolds-number tests. Stall is delaye d and poststall characteristics are improved when oscillatory blowing is ap plied from the leading edge region of the airfoil, whereas flap effectivene ss is increased when control is applied at the Bap shoulder Similar gains i n airfoil performance require steady blowing with a momentum coefficient th at is two orders of magnitude greater. A detailed experimental and theoreti cal investigation was undertaken to characterize the oscillatory blowing di sturbance, in the absence of external flow, and to estimate the oscillatory blowing momentum coefficient used in the cryogenic wind tunnel experiment. Possible approaches toward closed-loop active separation control are also presented. Based on the Endings of the present investigation, the applicati on of active separation control at incompressible Eight Reynolds number is within reach.