Characterization and Modification of the Flow Field Inside Dynamically Evolving Bubbles

The velocity field inside spherical-cap rising bubbles was measured quantitatively by ray-traced, planar laser-induced fluorescence (PLIF) and shadowgraphy and then used to calculate scalar transport properties for bubbles of different Reynolds numbers. The rising bubbles were seeded with a fluorescent aerosol and their internal velocities fields were educed by optic flow techniques while correcting for image distortions via a ray-traced reconstruction of the three-dimensional bubble geometries. Physics-based data assimilation was used to extrapolate missing velocity data near the bubble interface and interpolate the inner velocity field to high resolution, revealing a multi-scale toroidal vortex structure. The measured velocity fields were used to simulate the scalar transport characteristics across the bubble interfaces for the case of rate-limiting, gas-side resistance. The long-time Sherwood number for these spherical-cap bubbles differed from traditional solutions for spherical bubbles as a result of their Reynolds number dependent internal vortex structure. This internal velocity measurement technique has important implications for validating scalar transport models of bubbly flows, as well as enabling quantitative measurement of general, multi-phase flow scenarios.

This work is towards an Ph.D. degree under the supervision of Associate Professor Ian Jacobi, The Stephen B. Klein Faculty of Aerospace Engineering, Technion.