Interaction of bubble s and buoyant rigid particles with vortical structures Towards understanding bubbly turbulent flows

Abstract

Bubbly turbulent flows occur in many places, such as in chemical reactors and geophysical applications, besides interest from the drag reduction perspective using injected bubbles in a (water) boundary layer. In these flows, an important aspect is the interaction of bubbles with vortical structures, where bubble deformability is generally thought to play a crucial role. We experimentally investigate an idealization of these flows, namely, the interaction of a vortex ring in water with air bubble(s) and rigid equivalents of the air bubble, namely, buoyant rigid particles. In these idealized cases, the bubble / rigid buoyant particles are captured by the vortex ring, due to the low pressure within its core, leading to significant coupled interaction between the bubble/buoyant particle and the vortex ring. The thesis comprises of four main parts. In the first part, the interaction between a single vortex ring with a single deforming bubble is studied, with the focus being on the relative size of the bubble to the vortex ring quantified thorough a bubble to ring core diameter ratio or a volume ratio of the bubble to the vortex core. We are interested in the coupled dynamics of the bubble and the vortex ring, and hence measure the time evolution of both the bubble dynamics and the vorticity using high-speed shadowgraphy and time-resolved PIV, respectively. The results show the importance of the bubble to vortex core size ratio in determining the evolution of both the bubble and vorticity dynamics, which can be of importance in understanding flow modulation in bubbly-turbulent flow. An important aspect in these interactions is the deformability of the bubble. To better understand this aspect, we have studied in the second part of the thesis, the interaction between a rigid buoyant particle and a vortex ring. The results show large differences in some aspects of the interaction with the ring, while they remain qualitatively similar in others, and these differences and similarities are highlighted. In the third part o...