Entrainment and transport of air bubbles by vortex ring

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The entrainment and transport of air bubbles by a vortex ring are experimentally investigated. A vortex ring launcher, composed of a cylinder and a piston, is mounted on the bottom of a water tank. The cylinder diameter D0 and the piston stroke L0 are 42.5 mm and 100 mm respectively. The launched vortex ring, of which circulation is less than 20000, is of a laminar type. Air bubbles are injected from a needle, which is attached on the cylinder surface, into the vortex ring. The mean bubble diameter is 3.2 mm. The bubble motions relative to the vortex ring are found to be classified according to the strength of the vortex ring and the bubble flow rate. When the strength of the vortex ring is low, the bubbles are less affected by the vortex ring. With increasing the strength, the bubbles are favorably entrained into the vortex ring. The entrained bubbles distribute around the center of the vortex core. They are transported by the vortex ring when the strength of the vortex ring is large. The entrained bubbles hardly change the convection of the vortex ring. The radius of the vortex ring becomes larger at the position where a number of bubbles are entrained.