Abstract
The interaction between bubble motion and its surrounding liquid motion through a collision of a pair of zigzagging bubbles in a rest water column was experimentally investigated. A pair of hypodermic needles and a bubble generator utilizing pressure oscillation were employed in order to exactly extract and highly reproduce the interaction between liquid-phase motion and bubble motion. The recursive cross-correlation PIV technique made it possible to obtain the accurate velocity field of surrounding liquid motion around a pair of bubbles. The vorticity field around a pair of bubbles was calculated from the results of velocity field. First, various kinds of interactions (e.g. bouncing and coalescence) were found out from the results of bubble motion (e.g. velocity) after a collision. We classified such interactions of a pair of bubbles using the dimensionless number l/d. Second, we investigated surrounding liquid motion about the two cases of interactions after the bouncing. One is that only horizontal velocity of bubble decreased after the collision, the other is that both horizontal and vertical velocity decreased. At the former case, the vortical region generated at the rear of a pair of bubbles. Therefore as the reason for the decrease of bubble velocity, the shedding area of hairpin-like vortex is restricted. At the latter case, bubble wake flows into the area between bubbles and vortical region doesn't generate under bubbles after the collision. Hence, bubble wake overtakes a pair of bubbles after the collision, then, bubble velocity decreased.
