Abstract: Lift augmentation control is of great value for improving the aerodynamic performance and core competitiveness of large aircraft. Thus, to address the lift loss problem of a simple hinged flap at large deflection angles caused by severe flow separation, this paper takes the CHN-T2 wide-body transport aircraft standard model as the research object. The control effectiveness and underlying mechanism of synthetic jet actuation on flap separated flow and the resultant lift enhancement of the whole aircraft are revealed by numerical simulation. Through parametric studies, this paper reveals the influence mechanism of synthetic jet control on aerodynamic force variations and three-dimensional flow structure evolution, and obtains the effect of momentum coefficient, actuation angle, and actuation frequency on lift enhancement. The results show that the synthetic jet can effectively suppress flow separation on the flap surface and significantly increase the lift of the whole aircraft, achieving a 21.7% improvement in the average lift coefficient at an angle of attack of 8°. Analysis of the flow physics reveals how local perturbations propagate upstream from the flap region to the entire wing surface, along with the distinct roles of the blowing and suction phases of the synthetic jet. During the blowing phase, the synthetic jet injects high-momentum fluid into the boundary layer, enhances momentum mixing through induced shed vortices, and improves the flow's resistance to separation over the flap surface, with cross-flow playing a key role in the spanwise transport of the jet. During the suction phase, the local low-pressure effect near the jet exit accelerates the upstream boundary layer flow, thereby increasing the suction on the upstream main wing, which is the main reason why a perturbation applied near the downstream flap can still improve the flow over the entire main wing and the slat and thus enhance the overall lift of the aircraft. Further, the parametric effects are identified as follows: tangential jet orientation provides the best lift enhancement; increasing the momentum coefficient enhances lift but with diminishing returns; and the optimal actuation frequency is near the fundamental shedding frequency of the natural flow field.

Key words: synthetic jet, active flow control, CHN T2 standard model, lift enhancement, control mechanism