Characterization of a Griffith-Type Transonic, Laminar-Flow Airfoil

An experimental test campaign was conducted on a transonic Griffith-type airfoil to evaluate the effectiveness of its laminar flow qualities and boundary-layer flow control characteristics in the transonic regime. From the pressure distributions it was observed that the flow control application had a beneficial influence, allowing for a more aggressive pressure recovery downstream of the suction slot and higher recovery pressure values at the trailing edge. At M = 0.7 and alpha = 0 degrees, a net profile drag reduction of 10.70% and an increase in the L/D ratio of 14.68% was observed. PIV experiments were performed to characterize the wake velocity deficit produced by the airfoil, which showed good agreement with the drag performance across every Mach number condition. Surface-oil flow visualization experiments were also performed at the design Mach number of 0.7 to find that the airfoil experienced extensive laminar flow runs regardless of suction application, which were followed by a shock-induced laminar separation bubble before the slot location. In addition, Schlieren imaging experiments were performed at M = 0.7 to characterize the unsteady shock behavior. Acharacteristic shock oscillation frequency of 22.38 Hz was identified and observed to significantly stabilize with the application of suction.