NONUNIFORM RECOVERY OF VORTEX BREAKDOWN OVER DELTA-WING IN RESPONSE TO BLOWING ALONG VORTEX CORE

The transient characteristics of vortical structure over delta wing ar e studied experimentally when subject to single along-core blowing per turbation. Two half delta wing models with different sweep angle Lambd a = 60 degrees and Lambda = 75 degrees are investigated in this study. For Lambda = 75 degrees, the transient location of the onset of vorte x breakdown moves upstream monotonously toward the unperturbed locatio n. However, for Lambda = 60 degrees, there exists a chordwise region w here the upstream propagation of the onset location of vortex breakdow n is temporarily delayed. This delay causes the recovery process (upst ream propagation) of the onset location of vortex breakdown to be ''no n-uniform''. In fact, this non-uniform recovery may take on different appearance such as a plateau or overshoots and will last for several t imes of the convective time scale C/U-infinity. Furthermore, the locat ion of chordwise region corresponding to this delay depends strongly u pon the angle of attack (AOA). In additions, the non-uniform recoverin g characteristic of the onset of vortex breakdown may not be observed at high AOA if the blowing rate is too low. The mechanism governing th e nonuniform recovering characteristic is clearly verified through the LDA measurement and the phase-locked flow visualization. Evidently th e mutual interaction between the primary vortex structure and the seco ndary vortex is the key mechanism that leads to non-uniform recovering character over delta wing with sweep angle of 60 degrees