Supersonic flutter mechanism of "diamond-back" folding wings

Folding wings with adjustable geometry offer a viable solution for vehicles to adapt to complex and variable flight environments, while enhancing aerodynamic performance. This paper investigates the flutter mechanism and characteristics of the "diamond-back" folding wing under supersonic inflow by a ROM-based aeroelastic method. The evolution mechanism is analyzed by the characteristics of aerodynamic and flow field, system dynamics, and structural natural mode. The findings reveal that, firstly, as the Mach number increases, the flutter critical speed monotonically increases, while the flutter critical frequency exhibits fluctuations within a specific range. Secondly, the study reveals a pivotal transformation in the modal shapes at a 35 degrees swept-back angle that reshapes the system dynamics, transitioning from second and third-order coupled instability to first and secondorder coupled instability. Consequently, this nonlinear change significantly amplifies the flutter critical speed and reduces the flutter critical frequency. Lastly, the combined effect of Mach number and swept-back angle significantly influences the local flutter boundary. Under low supersonic speeds and large swept-back angles, a bow shock forms in the local flow field region, resulting in notable changes in pressure distribution. As the Mach number increases, the local flutter boundary exhibits a nonlinear trend of first increasing, then decreasing, and then increasing again. Conversely, as the swept-back angle increases, it demonstrates a nonlinear trend of first decreasing, then increasing. These insights provide valuable guidance for the aerodynamic and structural refinement of "diamond-back" folding wings, catering to sophisticated flight dynamics and environmental adaptability.