Aerodynamic design optimization of wide-Mach-number-range airfoils for hypersonic vehicles

Wide-Mach-number-range aerodynamic design is one of the bottlenecks in the development of horizontal take-off and landing hypersonic vehicles which experience subsonic, transonic, supersonic, and hypersonic regimes during their flights. However, optimized airfoil profiles for different speed regimes are often contradictory, which presents a great challenge to obtain satisfactory wide-Mach-number-range aerodynamic performance by a single configuration. Consequently, this article is aimed at the design of wide-Mach-number-range airfoils via an efficient global aerodynamic optimization design method based on surrogate models. First, a new wide-Mach-number-range airfoil is designed by taking both the hypersonic and transonic aerodynamic performance into account. The thickness of the optimal airfoil is 4%, and its lower surface features a double-"S" shape. Flow-field analyses indicate that the optimal airfoil compromises aerodynamic performance over a wide speed range, which has not been observed before. Second, a multi-objective optimization design of airfoils is further carried out, and a Pareto front of the lift-to-drag ratios from the transonic to hypersonic states is obtained. By analyzing the optimal results, the design principle of airfoils that compromises transonic and hypersonic aerodynamic performance is explained. Finally, the multi-objective optimization design of airfoils for three-dimensional wings is carried out. It is shown that the optimized airfoil for three-dimensional configurations has geometric characteristics similar to those obtained by two-dimensional optimization design, indicating that the flow mechanism around airfoils with small chambers and double-"S" lower surfaces also applies to three-dimensional situations and that the airfoil design is still of significance for wide-Mach-number-range hypersonic vehicles.