Optimization of positional parameters of close-formation flight for blended-wing-body configuration

In the present study, we study formation flight with two flying wing configurations. A low speed wind tunnel test is conducted to validate the accuracy of the Computational Fluid Dynamics (CFD). Two optimization procedures are implemented at a high subsonic speed. The free stream Mach number is kept at 0.85, the lead aircraft's angle of attack is 2°, and the following aircraft's angle of attack is 2° as well. The maximum lift-to-drag ratio of the following aircraft is achieved as the lateral spacing is 0.853 b, and the vertical offset is 0.022 b (b is the wingspan). As much as 24.7% induced drag reduction is achieved at the optimized state. A pair of counter-rotating vortices interact and weaken each other. By analyzing the Kriging model constructed in the optimization procedure, it seems that the following aircraft's aerodynamic performance is sensitive to lateral spacing and vertical spacing, but insensitive to longitudinal spacing in close-formation flight. The best drag reduction position places in the following aircraft's wing tip is positioned at the core of the leading aircraft's wing tip vortex.