On the Dynamics of Active Flow Control Over a Separated Airfoil Using Leading Edge Unsteady Blowing

Flow control has become universally accepted as an important technology that can potentially be implemented in future air and naval vehicles. It has been shown that flow control strategies can be effective in increasing lift, reducing or increasing drag, delaying or controlling separation, or even reattaching separated flows. However, there is still a need for better understanding of the physics that govern these processes. In order to address this, Time-Resolved Digital Particle Image Velocimetry (TRDPIV) was used in this experiment to quantitatively image the velocity field around a NACA-0015 airfoil at an angle of attack of 25 degrees and a Reynolds number of about 38,000. A slot was located approximately 0.1 chord lengths behind the leading edge and was used for pulsed flow injection at the natural shedding frequency of the wing. Ten cases with varying momentum ratios and pulse duty cycles were tested. A spatio-temporal analysis of the resulting flow fields was conducted. Reattachment and flow turning were observed, and the important features of the flow and their interactions with the wing are described. Analysis showed that the cycle-averaged momentum coefficient may govern flow behavior more than its peak value, and that the primary influence of flow control may be limited to the area within the pre-blowing separation region.