Control of Flow Separation Using Adaptive Airfoils

Abstract : A novel way of controlling flow separation is reported. The approach involves using an adaptive airfoil geometry that changes its leading edge shape to adjust to the instantaneous flow at high angles of attack such that the flow over it remains attached. In particular, a baseline NACA 0012 airfoil, whose leading edge curvature could be changed dynamically by 400% was tested under quasi-steady compressible flow conditions. A mechanical drive system was used to produce a rounded leading edge to reduce the strong local flow acceleration around its nose and thus reduce the strong adverse pressure gradient that follows such a rapid acceleration. Tests in steady flow showed that at M = 0.3, the flow separated at about 14 deg. angle of attack for the NACA 0012 profile but could be kept attached up to an angle of about 18 deg by changing the nose curvature. No significant hysteresis effects were observed; the flow could be made to reattach from its separated state at high angles by changing the leading edge curvature. Interestingly, the flow over a nearly semicircular nosed airfoil was separated even at low angles. By finding a "window" of angles of attack and airfoil profiles, it appeared possible to keep the flow attached through a maneuver. The shape change also modified the multiple shocks that form over the NACA 0012 airfoil at M = 0.45. Tests are underway to document the dynamic stall flow control that can be effected with the change of airfoil geometry using high-speed, real-time, phase-locked, interferometry. Detailed results from these tests are expected to be available for presentation at the meeting.