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M. Koch, Ch. Lechner, W. Lauterborn, R. Mettin:
"On the splitting of a single cavitations bubble during the collapse close to a wall";
Talk: The 12th European Fluid Mechanics Conference, Wien; 2018-09-09 - 2018-09-13.

Since quite some decades the collapse of a cavitation bubble in front of a solid boundary is object of investigation. The physics behind this issue covers the fields of complex
fluid dynamics, nonlinear acoustics, as well as non-equilibrium, multi-phase thermodynamics. Nowadays, advanced computational methods are able to resolve details on
microsecond and even nanosecond time scales. One example of the relatively complex
dynamical processes is the splitting of the collapsing bubble into several torus bubble
rings after liquid microjet impact. This has been seen many times in experiments and
also in the simulations done here with a finite volume solver.
The authors propose three separate phenomena that act together in the complex
bubble splitting process: The microjet feed, the liquid annular nanojet and the Blake
splash. The first phenomenon accounts for the geometrical issue of the continuously
progressing intersection line of the microjet surface (involuted upper bubble interface)
with the lower bubble interface and simultaneous overall bubble volume shrinking.
The second phenomenon is an annular jet into the bubble stemming from the tip of
the microjet impact zone. It was found by performing simulations with very high
spatial resolution. The third has been proposed in literature as a similar effect as
the splash of a drop impact onto a flat, free surface.
The simulations were performed with the two-phase-flow finite volume solver
compressibleInterFoam that bases upon the open-source software package foam-extend, which is a branch-off of OpenFOAM. The solver was modified such that it
is capable of handling the extreme conditions of a cavitation bubble and nonlinear
compressibility effects in both phases were included.