Investigation of the unsteady aerodynamic characteristics of a unmanned aerial vehicle with variable-sweep morphing

Unmanned aerial vehicles (UAVs) with variable-sweep morphing have good advantages in unsteady aerodynamic characteristics whereas most researches have focused on their steady-state benefits. In order to explore the relationship between these two aspects, a model of unmanned aerial vehicle used to do numerical simulations in variable-sweep morphing process is designed. To ensure the accuracy of the results, grid-independent verification, the time step selection and verification of dynamic mesh technique have been carried out. As there are so many factors that influence the unsteady aerodynamic characteristics, we make a comparison in different conditions such as the morphing period, angle of attack (AoA), and Mach number to analyze the unsteady aerodynamic characteristics. The results demonstrate that the unsteady aerodynamic characteristics curves of morphing wing during shape morphing are presented as hysteresis loops around the corresponding quasi-steady curves and that the loops deviate largely from the curves. This indicates that there is a large difference between the unsteady aerodynamic characteristics and the corresponding quasi-steady aerodynamic characteristics in the process of wing sweep varying, which needs to be taken into consideration specially. Meanwhile, we also analyze the flow field mechanism to compare the flow structure hysteresis effect and the additional velocity effect. In this paper, the main effect is the flow structure hysteresis effect.