Flow control over airfoils

Stall Delay of a NACA0018 Airfoil by Traveling Wave Actuations

Large eddy simulations (LES) of a low Reynolds number (Re=50,000) flow over a NACA0018 airfoil at the stall angle of attack (AOA) of 15 degrees are performed. The suction side of the airfoil undergoes a surface morphing in the form of backward (opposite to the airfoil’s forward motion) traveling waves. The surface morphing deformations are simulated using our curvilinear immersed boundary (CURVIB) method to control the flow separation and enhance the aerodynamic performance. The amplitude of the morphing is in the range of a = 0.0005L to a = 0.008L (L: chord length of the airfoil), similar to the range that can be created via piezoelectric actuators. The simulations are alsoperformed for various reduced frequencies (f*= fL/U, f: frequency, U: free stream velocity) ranging from f* = 4 to f* = 16. The simulations show that the stall is suppressed, and the flow is reattached only within the reducedfrequency range of f* = 8 to f* = 12, and the amplitude of a ≥ 0.001L. The lift increases by at least 16% within these ranges, and the drag reduces by at least 59%. Increasing the actuation amplitude till a = 0.002L, the lift increases, and the drag reduces. However, at amplitudes larger than a = 0.002L, the lift decreases, and the drag increases. Regarding the frequency effect, increasing the frequency to f* = 8, the lift increases, and the drag reduces. However, beyond f* = 12, the lift reduced, and the drag increased.