Time-resolved three-dimensional measurement of bubble deformation and surrounding water velocity field using 4-D PTV and tomographic reconstruction*

Bubble dynamics have been studied for several decades, but still many interesting topics remain for more understanding about relationship between bubbles and ambient fluid. Especially, it has rarely reported to experimentally measure flow field with sufficiently large size of deformable bubbles. Here, we introduce an experimental technique to measure 3-D bubble geometry using tomographic reconstruction method and flow field near a deformable bubble using time-resolved three-dimensional particle tracking velocimetry (4-D PTV) with Shake-the-Box (STB) algorithm and vortex-in-cell sharp (VIC#) method. White LEDs and blue LED were utilized to illuminate bubble with deformation and seeding particles respectively. Projected bubble shapes were extracted to original images which were captured by 4 high-speed cameras. Bubble 3-D geometry was reconstructed by the projected bubble shapes and bubble properties like trajectory, rise velocity, equivalent diameter was calculated. The reconstructed bubble mimics bubble's wobbling and trajectory well. Also, bubble rise velocity and equivalent diameter has under 10% error with 2-D image processing results. High rise velocity and entrainment from ambient at bubble wake are observed as bubble rises. Bubble deformation generates various size of vorticities, which cause observation of vortex pairing near deformable bubble.