Wind Tunnel Simulation of Flow Control With Pulsed Impinging Air Jets.
- The technology of natural laminar flow airfoils presents an opportunity to vastly increase the efficiency of aircraft by decreasing the friction drag on the wing during flight. These airfoils however are much more susceptible to flow separation and stall conditions resulting in increased drag and loss of lift on the airfoil. Flow control represents a possibility to prevent separation on these airf... read moreoils allowing them to be used throughout the aeronautics industry. Separation control is achieved by artificially adding momentum to the flow or manipulating disturbances within the boundary layer. Extensive research has been performed investigating the effect of exciting the boundary layer physically or acoustically with mixed success. Significant control has been achieved however with pulses of air injected directly into the boundary layer tangentially with the flow over the airfoil surface. In this paper the flow control potential of small, pulsed jets impinging on the airfoil surface is investigated experimentally using a wind tunnel. The effect of a single short pulse, generated at several different locations and angles on the airfoil was tested at a separated angle of attack. Using smoke wire flow visualization the effect of the pulse on separation, the wake size and all other characteristics of the flow were determined during and after the pulse passed the surface of the airfoil. The images produced were compared directly and quantitatively using image analysis software. This analysis successfully demonstrated that short duration impinging jets had an immediate effect on attaching the flow, and a long-term effect decreasing overall drag determined from the wake size. Additionally it was shown that the orientation of the jet had a significant effect on the flow behavior, and the shape of the pulse itself. These experiments generated sufficient proof of the efficacy of impinging jets for separation control and determined several highly effective orientations of the jet for as a basis for more quantitative research.read less