Optimization of lift-to-drag characteristics for high-speed wing-in-ground effect based on the Kriging model

In order to improve the aerodynamic performance of high-speed wing-in-ground effect vehicle, the global aerodynamic optimization method based on the Kriging model was adopted. The optimization of wing-in-ground effect at Ma=0.2, Ma=0.3, Ma=0.5 and Ma=0.8 was carried out with the aim of increasing the lift-drag ratio. The aerodynamic performance improvement included two aspects. One was from the ground effect, the drag force reduction at Ma≤0.5, and lift force increase at Ma=0.8. The increase of 31.6%, 55.0%, 101% and 31.1% in lift-drag ratio by the ground effect was achieved compared with these cases without the ground effect. The other one was from the configuration optimization. With the increase of Ma, the leading-edge radius of the optimized airfoil decreased, the maximum bending position moved downstream, the airfoil thickness decreased and thus the lift-drag ratio of the optimized airfoil increased by 12.8%, 13.03%, 7.45% and 38.3% when compared with the lift-drag ratio of original NACA4512 airfoil. The aerodynamic performance of the optimized airfoil showed that the lift-to-drag ratio of the airfoil increased with the decrease of ground clearance, with the increase of the angle of attack the lift-to-drag ratio increased first and then decreased, but under the condition of high subsonic speed and low angle of attack, the airfoil was too close to the ground, a shock wave was formed on the lower surface of the airfoil, which resulted in the decrease of the lift-to-drag ratio of the airfoil.