Active Flow Control for Reduction of Fluctuating Aerodynamic Forces of a Blunt Trailing Edge Airfoil

Abstract

Vortex shedding from the base of two dimensional bluff bodies is accompanied by three dimensional wake instabilities. These instabilities manifest as streamwise and vertical vorticity components which occur at a certain spanwise wavelength. The spanwise wavelength of the instabilities (λz) depends on several parameters, including profile geometry and Reynolds number. The present study aims to determine λz for a blunt trailing edge airfoil, which is comprised of an elliptical leading edge, followed by a rectangular section. Results of numerical simulations of flow around the airfoil at Re(d) = 500, 800, 1200, and 17,000, and flow visualization at Re(d) = 2200 indicate that λz has an average value of 2.2d. An active flow control mechanism based on the three dimensional wake instabilities is proposed, to attenuate the fluctuating aerodynamic forces of the airfoil. The mechanism is comprised of trailing edge injection ports distributed across the span, with a spacing equal to λz. Injection of a secondary flow leads to excitation of the three dimensional instabilities and disorganization of the von Ka´rma´n vortex street. Numerical simulations at Re(d) = 500 and 17,000 indicate that the flow control mechanism can attenuate the fluctuating aerodynamic forces significantly, and reduce mean drag using a relatively small injection mass flow rate.