Experimental study of high-speed phenomena involving bubbles and free surfacesbubble growth in microgravity and fast lifting of a plate from water surface

Resumen

This thesis addresses two different problems with a common link: both are experimental studies where the effect of gravity does not play an important role. While the first one is in microgravity conditions, the other one shows an acceleration much greater than gravity. As a consequence, this dissertation is divided into two parts: growing bubbles in gas-supersaturated liquid in microgravity and fast lifting of a plate from a water surface. In the first part, the diffusion-driven growth of a dense bubble cloud is studied in gas-supersaturated liquid in microgravity conditions. Understanding the diffusive-driven dynamics is relevant in several modern technologies such as space manufacturing or chemistry processes as well as in the formation of the small planetary bodies if we move to the geological field. On Earth’s conditions, it is not possible to observe this purely diffusion-driven growth for more than 100 ms since the gravity induces buoyancy effects that affect these dynamics. Thus, we carried out experiments in which a bubble cloud grows in aCO2-supersaturated water in microgravity using the drop tower of the German Center of Applied Space Technology and Microgravity (ZARM). In the experiments, the evolution of the bubble cloud can be observed for more than 3 s as well as their interactions and competition to access the CO2 available in the bulk liquid outside the cloud. Firstly, we show the details of the experimental setup that we use to perform these experiments and some preliminary results related to the individual growth of large bubbles and the time evolution of the gas volume of the cloud. Then, we report the existence of different regimes where the bubble cloud presents different growth rates in our experiments. Finally, we suggest a model that describes these regimes and their corresponding growth rate, qualitatively. In the second part, we address experimental research regarding the fast lifting of a circular disc from a water surface. For naval and ocean engineering it is essential to model the force that a structure must withstand when it impacts or exits the water. Since full-scale numerical simulations are usually impractical for this purpose, several analytical or semi-analytical approaches have been developed over the years. Due to the complexity of the free surface flows involving both numerical and analytical computations must be validated against experiments. With this idea in mind, here we report the results of the experimental measurements of the hydrodynamic force acting on a plate that is lifted from the water surface and starts to move upwards suddenly at an acceleration much larger than gravity, a ≫ g. Furthermore, we include the hydro-elastic effect that we observed in the experiments in the solution of the asymmetric of the water exit problem. Our work focuses on the early stages of the disc motion when the suction and inertial forces are the most relevant. Thus, the experimental set-up is described firstly, then we compare the experimental results against the linearised theory of the water exit proposed by Korobkin (2013). Finally, as a consequence of the experimental observations of the hydroelastic interaction between the disc and the liquid, the problem of the water exit is reformulated and solved taking into account this effect.