The risk of wake vortex encounter is a major issue in aviation. This is notably true in the vicinity of airports during take-off and landing. In order to reduce wake vortex encounters, conservative separation distances are applied. However, these distances impede on the increase of the frequency of arrivals and departures at airports by the steadily increasing traffic.
In the present work, an analysis of the control of the two-dimensional vortex dynamics close and at the ground as a mean to reduce the separation distance is carried out. The behavior of vortices in ground effect has been a much investigated subject, motivated by this aviation issue but also by wall bounded turbulence (Stephan et al. 2013). It has been demonstrated that vortices (Harvey et al. 1971) rebound at the ground instead of going sideways like in the inviscid situation (Lamb 1932). Vortex rebound causes vortices to stay longer above runways and increase the risk of encounters.
Two control strategies are described in order to alleviate the aforementioned issue. The first one is based on an optimal perturbation approach aiming at mitigating vortices by increasing perturbations growth.
An analysis of the effect of the perturbation symmetry and horizon time, along with a physical mechanism of the transient growth processes is achieved. The second approach is based on the optimal control of the vortex position through the implementation of active blowing/suction at the ground. The maximization of the lateral position of the vortices is achieved with the idea of suppressing vortex rebound, and promoting an inviscid like kinematics of the vortices (the vortices move sideways out of the runway). The method achieves a 50% increase in the lateral position of the vortices. A physical analysis of the change induced by the control on the flow is detailed.