| dc.description.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 of the thesis, we go one step closer to bubbly-turbulent flows, by
investigating the interaction of a vortex ring with a number of bubbles or a bubble swarm, with the
capture of the bubbles by the ring being a continuous process here. This is followed by a study of an
application of bubbly-turbulent flow, namely, drag reduction (DR) in a water boundary layer by
injection of air bubbles into a fully developed turbulent channel flow. As most of the practical
applications related to DR takes place in seawater, we have investigated the effect of salt
concentration on the bubble dynamics and hence DR. In these cases, the salt plays a crucial role as it
prevents bubble coalescence and hence significantly alters the bubble sizes and therefore the drag.
Overall, the above studies help better understand bubble interaction with vortical structures in
bubbly turbulent flows. | en_US |
