Session G10: Bubbles: Nucleation and Coalescence

Inertial collapse of individual bubbles near a solid surface

Inertial collapse of cavitation bubbles is an essential research topic to a variety of applications ranging from naval hydrodynamics to medicine and energy sciences. The bubble implosion, which concentrates energy into a small volume, can produce high pressures and temperatures, emit strong shock waves, and radiate visible light. One of the main consequences of cavitation is structural damage to neighboring surfaces. To better understand such flows, we use highly resolved numerical simulations of Rayleigh collapse of a single bubble as well as a bubble pair near a rigid wall. We explain that the presence of a rigid boundary and the inter-bubble interactions hinder the energy concentration, give rise to the momentum of non-converging motions, break the flow symmetry, and leads to lower pressures and temperatures. By developing scaling laws for certain collapse properties, we illustrate that single bubbles collapse in a universal, thus predictable fashion. However, collapse of a bubble pair shows a far more complicated behavior and breaks the single-bubble scalings. Thus, the value of such simulations to develop scaling laws for the collapse of many bubbles is debatable at the present time.   

Acceleration-induced cavitation and surrounding pressure in a short liquid column

Cavitation emerges due to sudden acceleration of a liquid (e.g., an impact to the liquid-filled container, the valve operation in a pipe system) and can cause severe damages on surrounding structures. This presentation mainly focuses on the dynamics of acceleration-induced cavitation bubbles and surrounding liquid pressure in a liquid-filled container. We firstly show the criteria for the onset of the acceleration-induced cavitation in a short liquid column. We then investigate the interaction between the dynamics of cavitation bubbles and the pressure field using a high-speed camera and a pressure sensor. Finally, we discuss the impulsive force upon the collapse of cavitation bubbles.   

Vortex interactions between the bubble pairs rising side by side in viscous liquids

The present study focuses on the importance of the vortex structures during the interactions between the bubble pairs rising side by side. Specifically, we identify that if there are standing eddies behind the bubble rear, the bubble pairs will repel each other after being released, and whether they will show a subsequent repeated-bounce or not depends on the rising behavior of the isolated bubble and the fluid properties. Moreover, the repeated-bounce behavior is actually a manifestation of the zigzag motion of isolated bubble. By contraries, the bubbles tend to attract each other after being released if there are no standing eddies behind them.However, whether they will coalesce or bounce after "kissing" is dependent on the development of the vortex structures. A thorough investigation explains why different bubble interactions are observed in water by changing the bubble size or their separated distance in the experiments from the aspect of the wake structure. Moreover, different vertical magnetic fields are further applied onto the bubble pairs to verify that it is actually the vortex interactions rather than the collision velocity that produces different bubble interactions