Numerical simulation of unsteady aerodynamic characteristics for a variable-sweep aircraft

Variable-sweep aircraft can actively change the sweep angle of the wings during flight, causing corresponding changes in the flight envelopes. Aerodynamic forces and moments are both time-varying and dynamic during different sweeping processes. The static aerodynamic characteristics are insufficient to meet the design requirements of modern intelligent variable-sweep aircraft. In this work, a numerical simulation method for studying the unsteady aerodynamic characteristics of variable-sweep aircraft is proposed. An overset grid method is used to numerically simulate a variable-sweep aircraft geometry. The numerical simulation results are obtained, which are well compared with the experimental data. The flow field state at the initial position of the aircraft is analyzed, and the lift coefficient and pitch moment coefficient show dynamic hysteresis loops during the unsteady process. At the same sweep angle, the lift coefficient and pitch moment coefficient during forward sweep are both large, while those during the backward sweep are small. The mechanism of unsteady aerodynamic characteristics is studied. It has been found that during the sweep, the additional velocity generated by the wing movement is the key factor leading to the generation of dynamic hysteresis loops. The additional velocity causes changes in the flow field vorticity during forward and backward sweep, resulting in changes in the pressure distribution on the upper and lower surfaces of the wing.