Development of Axial Flows in Wake Vortices due to End Effects

Experiments on the behavior of wake vortices after the end of lift production (end effects) are conducted in a towing tank. The experiments are a first step toward investigating the behavior of the wake vortices after the landing of an aircraft. The model used for the experiments is the DLR, German Aerospace Center F13, well known from previous investigations. After a straight translation at a constant speed, the F13 model in only wing configuration is decelerated at a constant rate to a complete stop to cease the lift production. After the beginning of the deceleration and the halt of the wing, two different disturbances are observed that travel through the cores of the wake vortices. These disturbances and their influence on tangential and axial flows in the wake vortices are investigated using conventional 2-D and stereo particle image velocimetry setups. First, wakelike axial flow is observed in the vortex core, then switching to jetlike axial flow, initiated by the first of the two disturbances (vortex bursting). After the first disturbance, the jetlike flow prevails and increases in magnitude until the second disturbance arrives (helical-like). The spatial–temporal behavior of the disturbances, including their propagation velocities, is presented and discussed.