Airfoil Aerodynamic Performance Enhancement by Manipulation of Trapped Vorticity Concentrations using Active Flow Control
DeSalvo, Michael E
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The mechanisms of aerodynamic flow control over lifting surfaces in which global, large-scale changes in aerodynamic characteristics are engendered by momentum injection across the flow boundary are investigated in wind tunnel experiments. Due to the interaction of spanwise arrays of surface-mounted fluidic actuators with the local cross flow, the global flow field can be altered fluidically. The utility of this approach for aerodynamic flow control in the absence of moving control surfaces is demonstrated in the limits of fully-attached and separated cross flows. In the present investigations, the actuation frequency is selected to be sufficiently high to be decoupled from global flow instabilities. The changes in the aerodynamic loads are attained by leveraging the generation and regulation of “trapped” vorticity concentrations near the surface to alter its aerodynamic shape. Diagnostics include measurements of the aerodynamic forces and moments and of distributions of static pressure on the airfoil surface, and particle image velocimetry (PIV) of the flow over the airfoil and in its near wake. The present investigations have demonstrated that when the base flow is fully attached (at low angle of attack) fluidic actuation alters the aerodynamic characteristics of an airfoil leading to controlled changes in lift and pitching moment along with a significant reduction in form drag. The effectiveness of actuation for mitigation of the adverse effects of separation is demonstrated on a high-lift flap system. It is anticipated that flow control augmentation of the performance of current and future flight platforms will ultimately enable significant mechanical simplification with savings in both weight and maintenance costs.