Effect of pitch down motion on the vortex reformation over fighter aircraft

The aerodynamic characteristics of a realistic aircraft undergoing high amplitude pitching motions ranging from angle of attack 0° to 80° are studied using a combination of delayed detached eddy simulation (DDES) method and experimental approach with reduced oscillation rates κ=0.036, 0.054 and 0.072. According to the DDES-based results and experimental data, it is confirmed that asymmetric vortex structure reformation process can be induced by pitch down motion when sideslip angle β=0°, thereby leading to abrupt and substantial increases in both dynamic normal and side forces. In addition, the effect of pitching frequency on the asymmetric vortex redevelopment is also studied, it will be suppressed with the increase of the oscillation rate, and the bubble and spiral modes are observed to dominate the left and right vortex breakdown process respectively on the left and right upper surface.