渦間隔がヘアピン渦の融合に与える影響

抄録

It was well known that in the process of breakup of a vortex structure, the transition to turbulent spots rapidly progresses triggered by the generation of vortices in the spanwise direction. However, since multiple hairpin vortices exist even just before the breakup, it is not possible to confirm whether the vortices generated in the spanwise direction are the direct cause of the breakup. In addition, it is interesting to observe whether reconnection or marge occur of vortices when multiple hairpin vortices are in the vicinity. Therefore, to simplify this phenomenon, we artificially generated two hairpin vortices close to each other in the laminar boundary layer and investigated behaviors that occur between these vortices pair. In this study, we investigated two cases in which the distance between the hairpin vortices was about the width of the vortex and about twice the width of the hairpin vortex. If the distance between the two hairpin vortices was Δz+=40, which is about the same as the width of the vortex, the heads of the two hairpin vortices approach each other and join together. On the other hand, if the distance between the two hairpin vortices was Δz+=59, which is about twice the width of the vortex, the two hairpin vortices did not approach each other and traveled parallel to each other. Therefore, it was clarified that the two hairpin vortices joined when the distance between the two vortices was within twice the width of the vortices. Furthermore, the existence of a high-speed region in the center of the joined vortices implies that the two hairpin vortices did not merge into a single hairpin vortex, but rather that the legs of each vortex reconnected and formed a duplex vortex structure consisting of a large hairpin vortex with a counter-rotating U-shaped vortex inside it.