Bursting bubbles and the formation of gas jets and vortex rings

Bubble bursting is important in air–sea interactions, food science, and industry, but the process of the pressurized gas escaping from inside the bursting bubble is not well understood. The fluid dynamics of gas jets and vortex rings produced by the bursting of 440 µm to 4 cm diameter smoke-filled bubbles resting at an air–water interface is investigated using high-speed stereophotogrammetry. The initial speed of the gas jet released from the bubbles increases with parent bubble size until the Bond number reaches unity and subsequently increases more slowly. The slow, low Reynolds number jets characteristic of small bubbles are attributed to high film retraction speeds which produce relatively large holes in the bubble cap, and these jets roll up into spherical, slow-growing vortex rings which travel short distances. However, the low film retraction speeds characteristic of larger bubbles produce high speed, high Reynolds number jets emitted through relatively small holes which roll up into highly oblate, fast-growing, far-traveling vortex rings. The tiniest bubbles eject only a thin stem-like jet which does not form a vortex ring. Finally, a simple scaling relationship relating the gas jet Reynolds number to the square root of the parent bubble Bond number is proposed.