Transonic Buffet Suppression by Airfoil Optimization

The main buffet suppression techniques of aircrafts include active and passive flow control, aiming to reduce the impact of the fluctuating loads on the airfoil. These techniques are remedies after the airfoil design. The buffet suppression is not always considered in the aerodynamic optimization in the state of airfoil design because it is difficult to extract an appropriate key objective variable to indicate the flow stability. In this paper, the damping rate of disturbance, which is computed by the global stability analysis, can be used to indicate flow stability. Based on the global stability analysis, a transonic buffet suppression methodology by airfoil optimization is proposed. The objective is to improve the aerodynamic performance as well as the flow stability in the desired flight state. The RAE2822 airfoil is chosen as the initial airfoil. A benchmark of the unsteady aerodynamic configuration optimization design considering buffet suppression is developed. First, the numerical methods are verified and the damping rate of disturbance is chosen as a constraint in the aerodynamic optimization to extend the buffet onset. Then, the surrogate models constructed by the radial basis function interpolation are used to replace the computational fluid dynamics (CFD) solver. The teaching- and learning-based optimization (TLBO) is used. Finally, the aerodynamic and the flow stability characteristics of the airfoil before and after optimization are compared and analyzed. The proposed optimization framework can not only improve the aerodynamic characteristics in the cruise state but can also suppress the transonic buffet on higher angles of attack.