The evolution of the bubble collapse morphology between two cylinders within a confined space

This work investigates the dynamic bubble behaviors between two cylinders within a confined space using high-speed photographic experiments and Kelvin impulse theory. First, the evolution of the collapse morphologies of bubbles located at the origin and along the y axis between two cylinders is qualitatively investigated. The effects of the cylinder spacing and bubble ordinate on the characteristics of the bubble deformation and the liquid velocity are then explored. The variations of the bubble interface velocities, the roundness of the bubble cross section, and the bubble radius are quantitatively analyzed. The conclusions can be summarized as follows: (1) The experimental bubble collapse phenomena at the origin can be divided into three cases: hourglass-shaped collapse, "8"-shaped collapse, and capsule-shaped collapse. Bubble collapse at the y axis can also be divided into three scenarios: awl-shaped collapse, spindle-shaped collapse, and inverted triangle-shaped collapse. (2) The cylinder spacing and the bubble ordinate significantly affect the experimental bubble collapse behaviors and the theoretical liquid flow field. (3) High-velocity liquid regions are generated around the bubble when it oscillates freely, and the nearby cylinders always lead to low-velocity regions between them and the bubble. The closer the bubble is to the cylinder, the smaller the low-velocity regions and the larger the high-velocity regions.