Ch. Lechner, W. Lauterborn, M. Koch, R. Mettin:

"Jet formation from bubbles near a solid boundary in a compressible liquid: Numerical study of distance dependence";

Physical Review Fluids,5(2020), 9; 093604-1 - 093604-36.

A small spherical bubble of high internal pressure is inserted into water at constant ambient pressure as a model of a laser-induced bubble. Its subsequent dynamics near a flat solid boundary is studied in dependence on the distance of the bubble to the boundary by numerically solving the Navier-Stokes equations with the help of the open source software environment OpenFOAM. Implemented is the finite-volume method for discretization of the equations of motion and the volume-of-fluid method for capturing the interface between the bubble interior and exterior. The bubble contains a small amount of noncondensable gas that is treated as an ideal gas. The liquid is water obeying the Tait equation. Surface tension is included where necessary. The evolution of the bubble shape and a selection of pressure and velocity fields are given for normalized distances D∗=D/Rmax between 0 and 3 (D is the initial distance of the bubble center to the boundary and Rmax is the maximum radius the bubble would attain without any boundary). The value Rmax= 500 μm is chosen for the study. Normal axial-jet formation (∼100 m/s) by axial flow focusing is found for 0.24≤D∗≤3 and the change to a different type of axial-jet formation (∼1000 m/s) by annular-liquid-flow collision for bubbles very close to the solid boundary (0≤D∗≤0.2). The transition region (0.2<D∗<0.24) is characterized by additional inbound and outbound annular jets. Remarkably, the inclusion of the viscosity of the water is decisive to get the fast jets.

cavitation, bubble dynamics, jet

http://dx.doi.org/10.1103/PhysRevFluids.5.093604

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