The response and receptivity mechanism of wingtip vortex under the effect of external disturbance

Determining the optimal external disturbance to promote vortex decay remains a critical challenge in active vortex control. This study investigates the effects of various external disturbances on characteristics and decay of wingtip vortex generated by a rectangular half-wing model, as well as the receptivity mechanism to external disturbance of different frequencies simulated using a synthetic jet. Experiment results reveal that disturbances whose control frequencies (F+=0.067–0.133) close to vortex wandering frequency not only accelerate the decay of wingtip vortex but also induce more pronounced instability compared with higher frequency configurations. For the most effective case F+=0.067, the wingtip vortex expands and diffuses more quickly, exhibiting a nearly 35% reduction in peak circumferential velocity and a 10% decrease in total circulation. Moreover, the vortex core radius expands significantly, and the wandering amplitude increases by up to 30%. By using resolvent analysis, an optimal frequency of external disturbance to wingtip vortex is predicted and aligns closely with the synthetic jet's most effective attention frequency. The analysis results further reveals that disturbances near the critical layer forcing frequency (denoted as mode-3 frequency) enhance vortex receptivity and expand the critical layer of the wingtip vortex. This makes the vortex more susceptible to external disturbances, resulting in faster diffusion. These results suggest that the critical layer mode identified through resolvent analysis effectively triggers vortex instability, offering valuable insights for the design of efficient, physics-based flow control strategies.