During take-off and landing, powerful vortices are created behind an aircraft. Such vortices result from pressure differences between the upper and lower surfaces of the wing whenever a wing generates lift. The lift-generating process leads to the formation of a vortex sheet along the trailing edge which due to its unstable character finally rolls up into a single vortex on each side of the wing, thus forming a pair of counter-rotating vortices.
A number of experiments were conducted in the small towing tank of the Hamburgische Schiffbau-Versuchsanstalt (HSVA) using an underwater model of the Airbus A340. At a particular station along the tank where test conditions had stabilized, the flow field development over time was measured using a custom designed Particle Image Velocimetry (PIV) measurement system from Dantec Dynamics. The size of the measuring plane was 0.44 x 0.61 meters.