The influence of the gas on the dynamics of cavitation bubbles

Cavitation bubbles, extensively investigated in fluid mechanics, present enduring challenges in hydraulic machinery, while holding considerable potential for practical applications in biomedicine and sonochemistry. Despite more than a century of research, many aspects of cavitation remain poorly understood, especially with regards to the bubble's gaseous phase.The small-scale nature of cavitation in both time and space hinders direct measurements of the bubble contents, setting a limit for a complete understanding of the collapse, as well as the resulting phenomena, including rebound bubbles, shock wave emission, and luminescence. Moreover, the gaseous phase comprised of both incondensable gas and condensable vapour adds a further level of complexity to the problem. In this thesis, we investigate the dynamics of single cavitation bubbles generated in water with different dissolved gases. Our objective is to discern how the dissolved gas and the vapour pressure of the liquid influence the composition of the bubbles, and in turn their dynamics. To this end, we combine analytical models with experimental techniques using high-speed visualizations, dynamic pressure measurements, and fast photodetection.To probe the effect of the incondensable gas, we propose an investigation of single cavitation bubbles in water, systematically changing the air saturation level below the equilibrium concentration.While we detect minor differences in rebound bubbles and light emission, these findings may hold practical significance in real-world applications.We also propose a novel method for studying the influence of condensable vapour on the bubble dynamics. Here, we generate cavitation bubbles in aqueous ammonia, whose vapour pressure largely varies with the solution composition. A combination of various observations shed lights on non-equilibrium processes and vapour compression at bubble collapse, additionally giving insights on the possibility that bubble deformations may dominate energy dissipation mechanisms. Experiments in aqueous ammonia serve additionally as a basis for the development of a new analytical model for the estimation of the bubble's internal pressure. The model focuses on the early stage of the collapse, being therefore independent on the uncertainties of the final collapse stage.In an applied context, we investigate the role of dissolved gas in cavitation erosion-corrosion of metallic materials.By generating a cavitating jet in sodium chloride solutions, whose air saturation varies with the salt concentration, we identify variations in material loss. In this case, the dissolved gas does not affect cavitation bubbles significantly, but likely the interplay between erosion and corrosive reactions as a consequence of a trade-off between the oxygen concentration and the electric conductivity of the liquid.Overall, the outcome of this thesis helps in understanding the composition of the gaseous phase of cavitation and its effects on the bubble dynamics. The results may benefit practical applications, as well as improving the development of novel and sophisticated numerical tools.