Diffuse interface modelling of micro/nano cavitation bubbles and their interactions with elastoplastic walls

The cavitation phenomenon, namely the appearance and collapse of vapour/gas bubbles surrounded by their liquid, has been of great interest in the past decades. The reason behind this interest is related to the large variety of possible applications in which the dynamics of small bubbles is involved and play a relevant role in the generation of significant macroscopic effects. Examples of these applications can be found in many different disciplines, such as biomedicine, industrial engineering and industrial cleaning processes. Most of the applications aim to control the cavitation phenomenon in order to take advantage of its power and, at the same time, limit its destructiveness. In this thesis, in which a Diffuse Interface model is used to physically describe and capture the dynamic behavior of bubbles, I analyse the results of many numerical simulations designed to gain insights and knowledge in both the nature of the cavitation phenomenon itself, and the effects resulting from a number of possible circumstances and applications. The core of the thesis can be summarized in two main topics: bubble growth due to laser (energy) deposition, and bubble collapse near solid boundaries and the effects generated on them. In the former part, the Diffuse Interface model capabilities of describing a thermodynamically consistent evolution of a two-phase flow are exploited, to simulate the nucleation, growth and subsequent rebounds dynamic occurring when a bubble is generated through laser deposition. he results suggest that the model is able to capture the phase change and the breakdown wave emission occurring when the vapour bubble is forming. The latter is focused on a typical effect observed on mechanical objects interacting with liquid flows in which cavitation occurs. Bubble collapse is a highly energetic process, which is capable of damaging nearby objects. In this thesis, the aim is to numerically reproduce the first stages of this phenomenon, by coupling a Diffuse Interface model for the description of the fluid dynamics with an elastoplastic model for the description of the solid mechanics. The presence of a solid boundary near a collapsing bubble influences the dynamics of the fluid and allows for greater energy transmission from the fluid to the wall, resulting in larger deformations and deeper plastic indentation.