Experimental Investigation of Unsteady Blowing Effects on Coanda Flap Lift Performance

The present study investigates experimentally the lift gains generated by the superposition of a periodic actuation component on a steady component on an airfoil with a highly deflected Coanda flap, expected to yield significant lift gains over steady blowing or even on/off blowing. The experiment is carried out at a 1.5×106 Reynolds number, and due to the advantages of a water tunnel facility, at much smaller free stream velocity than in a comparable wind tunnel, which make it possible to capture a considerably larger portion of the flow dynamics. The periodic actuation is provided by two synchronized novel valves that facilitate the exploration of a large actuation parameter space, yielding the corresponding lift gain topology. The results clearly demonstrate the benefits of superimposing a periodic component on the steady actuation component for a separated or partially-attached flow, where lift gains of up to 35% of the steady blowing lift are reached and for the same lift value an up to 57% reduction in blowing expenditure is achieved. Additionally, exploiting the benefits of a water tunnel to capture a considerably larger portion of the flow dynamics, the means by which those unsteady blowing lift gains are achieved, is investigated, gaining deep insights into the flap wake behavior under steady and unsteady blowing. Furthermore, two unsteady blowing lift gain mechanisms are discovered and the associated processes by which additionally lift is generated are revealed. Übersicht