Experimental investigations on the unsteady characteristics of vortex breakdown over delta wing

Based on the dye visualization experimental results, the variation of vortex cores velocity along vortex axis and their wavelet characteristics and the unsteadiness of the vortex breakdown position were investigated for flowing over 70 deg delta wing. The multi-scale decomposition of signals of vortex core velocity can be achieved through wavelet analysis, significant high frequency signal occurred at vortex breakdown location. Spectral analysis was used to quantify the unsteady behavior of vortex breakdown location obtained from visualization. It was pointed out that the variation of vortex breakdown position belonged to low frequency oscillation, which was caused by the interaction between the right and left leading edge vortices. When the distance for the mean vortex breakdown position of the two vortices became close, the corresponding oscillation tended to become violent. Moreover, the reduced frequency of this oscillation is less than 0.2.