Laser-scanning particle image velocimetry applied to a delta wing in transient maneuver

A laser scanning technique, which utilizes a galvanometer scanner to produce particle-image photographs, is employed to investigate the flow over a delta wing undergoing pitching maneuvers at a high angle of attack. Use of a unique forcing system and a large-scale prism arrangement allow characterization of the instantaneous velocity field over the entire crossflow plane at a desired angle of attack.Contours of constant streamwise vorticity are calculated from the crossflow velocity field at various pitching rates. The vorticity distribution occurring during the pitch-up motion differs substantially from that on the stationary wing at the same angle of attack. During the pitch-up motion, the leading-edge vortex is remarkably coherent, in contrast to the disordered structure on the stationary wing. During the corresponding pitch-down motion, the vorticity distribution is quite similar to that on the stationary wing at the same angle of attack. This behavior is evident for a range of pitching rates.