Single cavitation bubbles: 3D dynamics with phase transition
funded by FWF project PIN1966625 in collaboration with DFG project KO 7038/2-1
Project Leader: Dr. Christiane Lechner
Abstract: Cavitation refers to the formation and – often violent – collapse of vapor bubbles in a liquid. It occurs in fast liquid flows (e.g. close to ship propellers), in intense acoustic fields or can be induced by locally boiling the liquid with a focused laser pulse. Cavitation is destructive when eroding surfaces like propeller or turbine blades. A controlled destructive action, on the other hand, can be employed therapeutically, for example for breaking mineral deposits in the human body. Central to cavitation is the physical process of phase-transition, where liquid rapidly is transformed to gas (vapor) and vice versa.
In this project we develop a novel three-dimensional numerical model to simulate cavitation bubbles, carefully accounting for evaporation and condensation. Unlike simplified models, our approach captures the complex interplay of fluid flow, heat transfer and phase transition in an accurate way. Of particular interest are three-dimensional situations, where, for example, non-uniform temperatures along the bubble surface and bubble splitting can be captured. To validate our model, we compare simulations against experimental data for cases, where the effects of phase-transition are particularly pronounced. In carefully controlled laboratory experiments, undertaken by our project partner at the Georg-August-University Göttingen (Germany), bubbles are generated in a vacuum chamber (low ambient pressure), in heated liquids (elevated ambient temperature) or by long pulsed lasers (non-homogeneous conditions along the surface of the bubble). Comparing simulated and measured bubble shapes and pressure signals will allow to refine the model and more and more increase the accuracy.
A particular configuration investigated in this project, relevant for medical applications, is cavitation induced by the absorption of long laser pulses near an optical fiber tip. A technique like that is used, e.g., in minimally invasive medicine to fragment kidney stones. By predicting the bubble dynamics and the forces, the laser generated bubble exerts on nearby objects (as, e.g., fiber tip or a stone) we will provide fundamental relations, that help to optimize the application. This part of the project is supported by our collaboration partner at the Institute of Biomedical Optics, University of Lübeck. This project will provide deeper insight into phase-transition processes in cavitation bubbles. Several fundamental aspects will be examined, that are relevant for a variety of technical and medical applications.
Project start: 1. 5. 2026
Cooperations
Dr. Max Koch, Georg-August Universität Göttingen
Dr. Robert Mettin, Georg-August Universität Göttingen
Prof. Dr. Alfred Vogel, University of Luebeck