The transient characteristics of vortical structure over delta wing are studied experimentally when subject to single along-core blowing perturbation. Two half delta wing models with different sweep angle A = 60 ° and A = 75 ° are investigated in this study. For A = 75 °, the transient location of the onset of vortex breakdown moves upstream monotonously toward the unperturbed location. However, for A = 60 °, there exists a chordwise region where the upstream propagation of the onset location of vortex breakdown is temporarily delayed. This delay causes the recovery process (upstream propagation) of the onset location of vortex breakdown to be "non-uniform". In fact, this non-uniform recovery may take on different appearance such as a plateau or overshoots and will last for several times of the convective time scale C/U~. Furthermore, the location of chordwise region corresponding to this delay depends strongly upon the angle of attack (AOA). In additions, the non-uniform recovering characteristic of the onset of vortex breakdown may not be observed at high AOA if the blowing rate is too low. The mechanism governing the nonuniform recovering characteristic is clearly verified through the LDA measurement and the phase-locked flow visualization. Evidently the mutual interaction between the primary vortex structure and the secondary vortex is the key mechanism that leads to non-uniform recovering character over delta wing with sweep angle of 60 ° 1

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