Analysis of bubble interactions in bidisperse bubble swarms by direct numerical simulation

Direct numerical simulations of bidisperse bubble swarms have been carried out using a finite difference/front tracking scheme. A number of bubbles were placed into a periodically continued box filled with still liquid. After an initial transient, the system settles towards a statistical quasi-steady state. For this stage, the average bubble motion and pair-wise bubble interaction as well as the liquid pseudo-turbulence have been evaluated. Varied parameters are the bubble size and number ratios, the deformability of the bubble surface, and the volume fraction of the bubbly phase. It is found that the mean bubble rise and fluctuation velocities as well as the liquid velocity fluctuations follow similar trends as in comparable mono-disperse bubbly flows but that the microstructure of a bubble size and/or shape class can be strongly distorted by the presence of another class. Most bubble pairs prefer a horizontal or near-horizontal alignment at relatively small centroid distance.