Study on transonic buffet suppression with flapping rudder

Structural fatigue and flight accidents may be caused by the oscillating loads induced by buffet in transonic flight, so transonic buffet control is becoming a hot topic in the field of aviation. An investigation based on unsteady Reynolds-averaged Navier-Stokes equations and Spalart-Allmaras(S-A) turbulence model is presented to study the suppression of resonant rudder on the transonic buffet loads in this paper. First, the buffet onset and frequency characteristics for a stationary NACA0012 airfoil are verified with the experimental data. And then, the validation of the resonant rudder are studied from the variables of initial rudder angle, amplitude, frequency and phase angle. The initial rudder angle can reduce the actual angle of attack of the airfoil by the down effect. The amplitude and frequency are main parameters. In the case of rudder with a frequency very close to the buffet frequency, resonance occurs and the amplitudes of the lift and moment coefficients increase rapidly. The phase angle is also an important factor. Lift coefficient has an decrease of about 60% at phase angle towards 270°. Therefore, resonant rudder may be a feasible open-loop strategy to suppress buffet loads with an appropriate and accessible combination of amplitude, frequency and phase angle.