Study of the interactions between rising air bubbles and vortex core of swirling water flow around vertical axis

• The precessional amplitude of the vortex core depends on the bubble flow rate.
• The bubbles reduce the water velocity in the lower horizontal cross-sections.
• The shape of the vortex funnel formed at the water surface is affected by the bubbles.

The interactions between rising air bubbles and the vortex core of swirling water flows in a cylindrical tank are experimentally investigated. A stirring disc mounted at the center of the tank bottom is rotated to produce swirling water flows around the central (vertical) axis of the tank, and small air bubbles are successively released from tubules mounted near the stirring disc. The bubbles rise helically in the swirling water flow because of the buoyancy force, and some bubbles are entrained into the vortex core. The precessional amplitude of the vortex core is enhanced by the bubbles when the bubble flow rate Qg is very low. But it decreases with increasing Qg when Qg is larger than a certain value. In the horizontal cross-sections near the stirring disc, the bubbles make the water flow field nonaxisymmetric and reduce the water velocity. The water velocity variation due to the bubbles affects the shape of the vortex funnel formed at the water surface.