Multiscale bubble breakup dynamics adjacent to a blade in unsteady turbulence within a bubble breaker

To comprehend the dynamic characteristics of multiscale bubbles in proximity to the propeller within unsteady turbulence, the large eddy simulation-fluid volume numerical method is employed to investigate the mechanisms of bubble fragmentation, coalescence, and ascent at varying sizes and stirring speeds. The findings indicate that the dispersion behavior of bubbles in the high velocity gradient region surrounding the blade is more pronounced than their ascent behavior. Regardless of bubble size, the formation speed of daughter bubbles is maximized at 350 rpm, with smaller bubbles exhibiting a tendency to break at elevated speeds. Coalescence of bubbles typically occurs in regions of negative pressure, driven by high velocity gradients and influenced by turbulent vortices. The ascent behavior of the bubbles is affected by the Eötvös (Eo) number and vorticity shedding, as they rise around the blade, gradually approaching and entering the main vortex area. The bubble fragmentation process is governed by the Weber number, which decreases with increasing bubble size. At 350 rpm, the critical Weber number remains constant at approximately 40, regardless of bubble size, indicating that 350 rpm is a stable crushing speed.