Evaluation of large-scale wing vortex wakes from multi–frame PIV measurements in free–flight laboratory

Abstract

Multiple-vortex systems of aircraft wakes have been investigated experimentally in a unique large-scale laboratory facility, the free-flight B20 catapult bench, ONERA Lille. 2D/2C PIV measurements have been performed in a translating reference frame, which provided time-resolved cross-velocity observations of the vortex systems in a Lagrangian frame normal to the wake axis. A PIV setup has been employed successfully using a multiple-camera array and a variable inter-frame time delay. The large-scale quasi-2D structures of the wake vortex system have been identified using the Q criterion based on the planar velocity gradient tensor, thus illustrating the temporal development of unequal- strength co-rotating vortex pairs in aircraft wakes up to vortex ages of two.