Oscillations, Waves, and Interactions - GWDG

Oscillations, Waves and Interactions, pp. 139–170
edited by T. Kurz, U. Parlitz, and U. Kaatze
Universitätsverlag Göttingen (2007) ISBN 978–3–938616–96–3
urn:nbn:de:gbv:7-verlag-1-06-7
The single bubble – a hot microlaboratory
W. Lauterborn, T. Kurz, R. Geisler, D. Kröninger, and D. Schanz
Drittes Physikalisches Institut, Georg-August-Universität Göttingen
Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
Abstract. Experimental and numerical work on single bubbles in liquids, mostly water, is
presented. The oscillation properties of acoustically driven bubbles from periodic motion to
period-doubling and chaotic dynamics are reviewed. Optic cavitation as a means to prepare
single bubble states in conjunction with high-speed optical observations is shown to enable
detailed investigations of bubble dynamics, in particular, fast bubble collapse at various
conditions. In this way, shock wave and light emission, jet and counter-jet formation near
solid walls and the associated erosive action on the surface could be elucidated. Molecular
dynamics studies are presented that allow a numerical view into the bubble interior that
hitherto is not accessible by experiments.
1 Introduction
A single bubble in a liquid is a remarkable object. In many cases it attains a spherical
shape due to surface tension and floats around in the liquid driven by the various
forces that it is susceptible to, notably pressure forces of all kinds from static to
acoustic, from buoyancy to drag. A single bubble, in a sense, is an artificial object, as
it likes to come in clouds and swarms. However, the single bubble is the building block
and starting point for describing more complex bubble configurations. Moreover,
through the concentrated effort of many a scientist it has been tamed to be kept
in place in a bubble trap for closer inspection [1], similar to the optical tweezer for
objects susceptible to electromagnetic forces (light waves) or the ion trap for keeping
ions in place with electric forces.
2 Single bubble in a sound field
It has been found that bubbles can be generated in liquids by sufficiently strong
sound fields, a process called acoustic cavitation. The bubbles formed subsequently
react to the pressure variations in the sound field. Sufficiently small bubbles attain a
spherical shape due to the surface tension of the liquid and start to oscillate radially.
Indeed, they can be considered as nonlinear oscillators driven by the varying pressure
of the sound. When dispensing with other forces (as buoyancy, for instance) tractable
models for the oscillation of a spherical bubble in a sound field can be formulated
with varying degree of sophistication.