Abstract:
Summary. The trafisient behaviour of leading-edge vortices over a delta wing subject to a sudden change of incidence is of importance in understanding the wing loadings that can occur in unsteady conditions of flight. In the experiments reported here, changes of incidence have been imposed on delta-shaped plates by application of a constant-velocity plunging motion for a limited time; other related unsteady motions are discussed in the Appendix. Ciné records of particle tracks and of dye filaments in a water tunnel have been analysed to trace the time history of vortex centres in cross-flow planes following the application of step-changes of incidence. The flows for various combinations of initial incidence, planform, plunging velocity and chordwise position have been examined. Results indicate that after the start of the plunge an effectively steady vortex system is established over the plate in a time approximately equal to that required for one chord length of relative forward travel. Where comparisons can be made, Dore's theoretical calculations of the manner in which the vortices move show fair agreement with the experiment. Effects of the transient movements of the vortices on lift distribution are discussed and the inference is drawn that the changes in the distribution of wing loading occurring for an increase of incidence are not simply reversed when the incidence is decreased.
