Control of Flow Separation over a Flapped Airfoil Using Low-Aspect-Ratio Circular Pins

Abstract

The implementation of an array of finite-span, low-aspect-ratio circular pins as a flow control method to mitigate separation over a flapped airfoil was investigated experimentally in a wind tunnel. The effect of an array of static cylinders, placed just upstream of a deflected control surface, on the separated flow over the control surface was explored via surface pressure and stereoscopic particle image velocimetry measurements. The array of pins was embedded in a turbulent boundary layer, where the height of the pins was approximately 2/3 of the local boundary-layer thickness. The static array of pins demonstrated a large reduction of the separated flow over the control surface, as well as a change in the global circulation, quantified by an enhanced sectional lift coefficient of and reduction in drag coefficient of . A secondary dataset was collected, which studied the effect imposed on the nearfield from a single pin that was either static or underwent dynamic motion (in the wall-normal direction), placed upstream of the deflected control surface hinge line. Results indicate that even a single pin (with diameter-to-airfoil span ratio of ) had a noticeable impact on the delay of separation, enhanced global circulation, and drag reduction. Overall, the features discussed have provided strong evidence of the potential that finite-span, low-aspect-ratio cylindrical pins provide as new actuators for flow control.