关键词: 跨声速, 时变马赫数, 数值虚拟仿真, NACA0012翼型, 嵌套网格, 激波, 激波/附面层干扰

Abstract:

The position， speed， as well as the attitude of the aircraft were continuerously in changing with time during the flight， which makes the flight simulation difficult and challenging， and the problems encountered in the flight of acrossing transonic region are more complicated. To explore the unsteady characteristics and influence mechanism caused by the time-varying Mach number effect during the transonic acrossing， the numerical flight simulation of NACA 0012 airfoil acrossing the transonic region was performed with the applications of the dynamic chimera mesh and the time-varing Mach number strategy， focusing on the changing characteristics and the mechanism of aerodynamic characteristics and the pressure center. The simulation results showed that， the nonlinear change of aerodynamic characteristics and the oscillation of the pressure center position were related to the position of the flow shock waves， the shock wave/boundary layer interaction， the flight speed varing and the angle of attack during the transonic acrossing flight. For the transonic acrossing with steady simulation， the curves of lift coefficients and pitching moment coefficients showed the trend of “two rises and two falls” with the increasing of Mach number， and the range of pits area in the curves expands with increase of the flight angle of attack. The drag coefficient diverged when approaching to the transonic region， and the corresponding diverging Mach number decreased with increase of the angle of attack. The airfoil pressure center is basically holding at the position of x/c=0.246 in the subsonic region， while the oscillation of the pressure center position decreased with increase of the angle of attack in the transonic region. and the pressure center position in the supersonic region is finally stable at the position of x/c=0.454. In the process of unsteady transonic acrossing simulation， the trend of aerodynamic characteristics changing is very similar to that of steady transonic acrossing process， but the change of aerodynamic characteristics and pressure center oscillation characteristics showed obviously the hysteresis effects due to the acceleration in the transonic acrossing process. The greater the flight acceleration， the more obvious the hysteresis， and the oscillation amplitude of the pressure center position weakened with increase of the angle of attack， as well as the increase of speed accelerations. The research conducted in the current paper can provide reference for the design of aircraft flight control system， the analysis of transonic aeroelastic stability and the evaluation of flight maneuverability， especially in transonic region.

Key words: transonic flight, time-varying Mach number, numerical flight simulation, NACA0012 airfoil, chimera grid, shock wave, shock wave/boundary layer interaction (SWBLI)