Surrogate-based aerodynamic shape optimization of a sliding shear variable sweep wing over a wide Mach-number range with plasma constraint relaxation

Considering both supersonic and subsonic aerodynamic performances in aircraft design is challenging. This challenge can be alleviated through morphing design or plasma flow control. Therefore, if they are both considered in the aerodynamic optimization, the results can be undoubtedly improved. In this study, first, a new sliding shear variable sweep design scheme which can change both the plane shape (such as the span and sweep angle) and the wing profile (such as the chord length and the relative thickness) is proposed and some information about the elastomeric skin scheme is given. Second, an efficient global optimization framework based on surrogate-based optimization algorithm is established for the aerodynamic shape optimization of this morphing wing. Third, two optimizations are conducted, wherein one considers the effect of plasma actuation while the other does not. Due to the complexity and large calculations required, the effect of plasma actuation is not directly considered in computational fluid dynamics simulation but is indirectly considered by relaxing the subsonic lift constraint, which assumes that plasma actuation can offset the lift loss. Therefore, it is called “plasma constraint relaxation”. In the two optimizations, three different configurations of the morphing wing which are 20°-, 30°- and 70°- sweep angle state, and three different flow conditions, which are subsonic (0.25 Ma), transonic (0.85 Ma) and supersonic (3 Ma) are considered. The results show that the comprehensive performance (objective function) improves by 12.6% with the effect of plasma actuation while it improves by 7.6% without the effect of plasma actuation after a two-round optimization. This suggests that the subsonic lift constraint, as an active constraint, significantly impacts the final optimization results. Finally, to verify whether plasma actuation can offset the lift loss, an experiment of nanosecond pulse dielectric barrier discharge plasma controlling flow separation is conducted to increase the subsonic lift of the optimization shape. The results show that the maximum lift increases by 18.1% when the actuation voltage is 8 kV and actuation frequency is 160 Hz and the lift loss caused by the constraint relaxation is 14.5%.