[Zurück]

Ch. Lechner, M. Koch, W. Lauterborn, R. Mettin, T. Hupfeld, G. Laurens, D. Amans, B. Gökce, S. Barcikowski:
"Jet formation of bubbles expanding and collapsing right at a flat solid boundary - a numerical investigation on the influence of viscosity";
Vortrag: 8. Workshop Kavitation, Vom Modell zur Anwednung, Kloster Drübeck; 29.11.2021 - 01.12.2021.

The dynamics of a single bubble generated by focusing a laser directly at a solid target is studied numerically for liquids with different viscosities. Numerical modeling sets in after recombination of the plasma, when the bubble has already formed. The model consists of a bubble filled with a small amount of non-condensable gas in a compressible liquid obeying the Tait equation of state. Initially, a hemi-spherical bubble under high internal pressure is placed directly at the solid. The subsequent dynamics, expansion and collapse, is investigated by solving the Navier-Stokes equations discretized with the finite volume method. The volume of fluid method is used to capture the interface between liquid and gas. The model is implemented in the open source software package OpenFOAM.

For three different liquids (water, PAO6, PAO40) the numerically obtained bubble shapes are compared to the shapes extracted from experimental images, showing excellent agreement. The dynamics of the bubbles is discussed. In particular, numerical simulations can resolve the formation of a very fast jet of the order of 1000 m/s, which results from self impact of an annular inflow during bubble collapse. With increasing viscosity the annular inflow is damped and jets with decreasing speed form by involution of the bubble wall. For millimeter-sized bubbles we find jet formation from self impact in water, jet formation by involution of the bubble wall in PAO6 and no jet formation in PAO40.

bubble dynamics, jet formation, cavitation, laser ablation in liquids