Airfoil Flow Re-energization and Separation Control via Manipulation of Artificial Large-Scale Motions

A separation control scheme was implemented on two airfoils to study the effects of controlling artificially-generated large-scale motions in a tripped boundary layer flow with a nonzero pressure gradient. A pitched upstream synthetic jet issued a train of vortices into the flow that was later manipulated by a low aspect ratio circular cylinder cantilevered into the local boundary layer (i.e., a static pin) and a jet-assisted surface-mounted actuator (i.e., a static pin with a synthetic jet orifice on the aft side). A NACA 63A210 airfoil, at low angle of attack with attached flow, was tested for boundary layer re-energization near the trailing edge region at a chord-based Reynolds number of Re_c = 3.2 x 10^5. In addition, a generic US Air Force transonic airfoil was tested at the same Reynolds number to assess the control of moderate trailing edge flow separation. Planar particle image velocimetry was conducted on the actuator centerline and revealed that separation could be mitigated with either a passive or active version of the control scheme. The passive and active controls comparably improved centerline velocity for the NACA 63A210 model. The active control led to the greatest improvements in streamwise velocity and centerline separation reduction for the second airfoil, relative to the uncontrolled large-scale motion generation case.