Effect of Pitch Rate on Near-Surface Topology on a Delta Wing

The near-surface flow structure and topology on a delta wing of moderate sweep angle are investigated using a technique of high-image-density digital particle image velocimetry. The focus is on the time evolution of the surface topology during relaxation of the flow after termination of a pitching maneuver for a wide range of pitch rates. The near-surface patterns at the instant corresponding to termination of the maneuver are a strong function of the magnitude of pitch rate and show substantial differences. On the other hand, irrespective of the severity of the flow distortion at the end of the pitching maneuver, the relaxation of the flow involves the same sequence of universal topological states. Furthermore, it is demonstrated that there exists a critical universal state that marks an abrupt transformationbetween twodistinctly different states of thenear-surface topology.Moreover, it is demonstrated that the changes of the topological features observed during the early stages of the relaxation process are analogous to the alterations of the surface patterns obtained for the stationary wing at smaller angles of attack.