Experimental investigation of the motion of a bubble in a gradient of turbulence

The role of the turbulence-intensity gradient upon the motion of a bubble i s investigated. Isolated bubbles are put into a turbulence field, which is isotropic and decreases exponentially in intensity in the z-direction. Expe riments are carried out under microgravity conditions, so that the buoyancy is negligible. Bubbles are observed to move in the z-direction. Their mean velocity is found to result from a balance between the mean-pressure gradi ent and the Reynolds-stress gradient. (C) 1999 American Institute of Physic s. [S1070-6631(99)04010-6].