Relation between Wake and Zigzag Motion of a Single Bubble

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In the present study, a transition mechanism to explain the change in the motion of a single ascending bubble from linear to zigzag was investigated experimentally. We focused on the relationship between bubble motion (gravity-center motion and surface motion) and hairpin-like vortex motion. First, the bubble motion was visualized using the infrared shadow technique (IST), and the gravity-center motion and surface motion were quantified. Second, the bubble wake structure and its motion were visualized with the laser induced fluorescence using HPTS (LIF/HPTS) method. From the LIF results, position fluctuations of the point of the hairpin-like vortex leg on the bubble rear surface (wake motion) were quantified. From these results, a close relation between the bubble motion and the wake motion was discussed. Furthermore, a relation between the wake motion and the lift force acting on the bubble was discussed. We concluded that the relations between them play an important role in zigzag motion. In addition, we tentatively concluded that bubble shape deformation observed just after the launch was the first trigger for the zigzag motion.