Oscillations of leading-edge vortex breakdown locations over a delta wing

This paper presents an experimental investigation of the oscillations of the leading-edge vortex breakdown locations over a slender delta wing with a 75 deg sweep angle. Here, a new mechanism is proposed, the vortex-secondary-flow interaction, responsible for the quasi-periodic antisymmetric interaction of the leading-edge vortex breakdown locations; the induced secondary flow in the symmetric plane continuously transfers the disturbance induced by the leading-edge vortex breakdown from one semispan to another, as well as the corresponding positive feedback. Therefore, the oscillations of the leading-edge vortex breakdown locations are synchronized in an opposite phase by the induced secondary flow. The experimental results are consistent with this interaction mechanism. Moreover, a new small-scale oscillation of the leading-edge vortex breakdown location is observed upon the application of an improved peak-valley-counting method. Its frequency is in the range of the helical mode instability.