Direct Lift Control of an Airfoil using Distributed Active Bleed

The spanwise load distribution of a 3-D wing model is regulated in wind tunnel experiments using distributed autonomous active air bleed driven through surface openings by inherent pressure differences in flight. Distributed bleed is shown to be effective for direct lift control (DLC), in which lift is varied without changing angle of attack, as an alternative to conventional movable electromechanical control surfaces. Bleed flow is driven from the pressure surface to the suction surface through slots in the mid-span section of the model (4% open area on each side) and interacts with the cross flow over the surface to produce large-scale changes in the flow field and in the aerodynamic loads (measured using high-precision load cells). It is shown that, depending on operating conditions, the bleed leads to a lift reduction of up to 28% or increase of up to 11%, with minimal change in pitching moment. Stereo PIV measurements of the wake in a streamwise-normal plane downstream of the model show the effects of bleed on the distribution of streamwise vorticity in the wake and the tip vortex and on the spanwise loading of the wing.