Near-surface topology and flow structure on a delta wing

The streamlines, and the corresponding patterns of velocity and vorticity, are characterized on a plane immediately adjacent to the surface of a delta wing using a laser-based technique of high-image-density particle image velocimetry. This technique provides the sequence of instantaneous states, as well as the corresponding time-averaged state, of the near-surface streamline topology and the associated critical points. These topological features are interpreted in terms of patterns of averaged and unsteady velocity, and averaged vorticity, which allow identification of regions of unsteadiness along the surface of the wing. These representations of the flow patterns on the stationary wing are also employed for the case of the wing subjected to small-amplitude perturbations in the pitching mode. Perturbations at or near the inherent frequency of the predominant unsteady event on the stationary wing yield substantial changes of the surface topology and flow structure. Furthermore, response of this topology and flow structure to transient, ramplike pitching motion is addressed to define the succession of states during the relaxation process immediately after cessation of the wing motion.