| Interactions of a quasi-two-dimensional vortex with a stationary and oscillating leading-edge were examined using a scanning laser version of high-image-density particle image velocimetry (PIV). The incident vortex street was generated by sinusoidal oscillation of an airfoil located upstream of the leading-edge. The reduced frequency of vortex convection and the oscillation of the leading-edge were equal, allowing the phase shift between them to be varied independently. At the lower of two Reynolds numbers, a well resolved time sequence of the interactions was obtained.; PIV images provide the first quantitative description of the edge interaction, employing instantaneous vorticity distributions and streamline patterns to reveal new topological features. These include the approach, deformation and splitting of an incident clockwise vortex, and the generation of tip and surface vortices on the lower surface of the stationary leading-edge.; Six stages of vortex development along the lower surface were also defined, including splitting of the tip vortex. The development of the tip vortex in the first three stages was found to depend more on the incident flow field and the resulting flux of vorticity from the upper surface. In the latter three stages, development depended more upon the mutual interaction of the tip and surface vortices with the lower surface.; Compared to interactions with a stationary leading-edge, oscillation of the leading-edge at {dollar}phi=0spcirc{dollar} with respect to the incident vortex produced tip and surface vortices of much higher circulation. When the leading-edge oscillated at {dollar}phi=180spcirc,{dollar} no tip or surface vortices were formed. This suggests the induced force on the edge will be much greater when the leading-edge oscillates at {dollar}phi=0spcirc,{dollar} and substantially reduced when the edge oscillates at {dollar}phi=180spcirc,{dollar} relative to the incident vortex. Consequently, variation of the phase angle of the leading-edge oscillation may be used to control unsteady loading and noise generation resulting from vortex interactions. |
