Étude des instabilités des tourbillons de sillage d'avion en effet de sol

Abstract

With the increasing use of air transport for passengers, traffic increasingly dense near airports is formed. The wake of each aircraft represents a potential threat to the stability of a plane in the vicinity of this wake. This threat is even greater when the plane is near the ground, as in the case of an aircraft in landing and takeoff phase. To minimize risks, a safe distance must be imposed between the aircraft leader and follower aircraft. To increase air traffic, the distance should be minimized. To do this, a study of the wakes’ natural dissipation mechanisms in ground effect is achieved. This study is obtained by numerical simulations and linear stability analyzes of a pair of counter-rotating vortices. DNS models the configuration of a pair of counter-rotating vortices in ground effect, while the analytical stability study models a pair of counter-rotating out of ground effect. It is noted for in ground effect configuration the main vortices of the pair mutually induce a downward velocity. At ground approach, boundary layers are formed and eventually separated to become secondary vortices whose circulations are less than the principal’s. The study of the vortex perturbation field from the numerical results shows a typical bending mode instability in the secondary vortices and the beginning of the appearance of an elliptical instability in the main vortices. In addition, the study of the linear stability of the subsystem consists of a primary vortex and secondary vortex which corroborates the wave numbers identified using numerical simulations. Now, it is deduced that only the ratio of circulations (Λ) and the radius of the secondary vortex (a2/d) are needed to predict the most unstable wave number from theoretical analysis of stability the vortex system. Subsequently, the effect of a side wind is considered. The effect of the wind is equivalent to adding a background vorticity. This background vorticity has the effect of making the vortex system asymmetric. The left and right vortex subsystems, each composed of a main vortex and a secondary vortex, interact differently depending on the vorticity resulting from the superposition of the background vorticity and that of the subsystem. In this in ground effect configuration with a crosswind, the ratio of circulation (Λ) and the radius of the secondary vortex (a2/d) are evaluated. These two parameters are used to determine, with the same linear stability theory outlined above, the most unstable wave number leading to the dissipation of the aircraft wake vortices.

Date	21 Jul 2017
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Louis Dufresne (Supervisor)