On the dynamics and breakup of a bubble rising in a turbulent flow

Experimental investigations of the dynamics of a deformable bubble rising in a uniform turbulent flow are reported. The turbulence is characterized by fast particle image velocimetry. Time-resolved evolutions of bubble translation, rotation, and deformation are determined by three-dimensional shape recognition from three perpendicular camera views. The bubble dynamics involves three mechanisms fairly decoupled: (1) average shape is imposed by the mean motion of the bubble relative to liquid; (2) wake instability generates almost periodic oscillations of velocity and orientation; (3) turbulence causes random deformations that sometimes lead to breakup. The deformation dynamics is radically different from that observed in the absence of a significant sliding motion due to buoyancy. Large deformations that lead to breakup are not axisymmetric and correspond to elongations in the horizontal direction. The timescale of decay of shape oscillations is of the same order as their natural frequency f(2), so that breakup always results from the interaction with a single turbulent eddy. This overdamping causes the statistics of large deformations and the statistics of breakup identical to the statistics of turbulence. The bubble response time f(2)(-1) however controls the duration of individual breakup events. (C) 2011 American Institute of Physics. [doi:10.1063/1.3648035]