Oscillations, Waves, and Interactions - GWDG

Acoustic cavitation 195
structures if suitable heuristic assumptions are included. Some examples of numerical
structure reconstruction have been presented, and the results are qualitatively
and partially even quantitatively satisfying.
Possible extensions of the proposed particle model approach are manifold. The
most relevant physical phenomena that have been neglected in the presentation so far
are probably the streaming of liquid and the modification of the initial sound field by
the presence of a finite bubble density. The streaming should have a distinct influence
on the (re)distribution of (passive) microbubbles and thus bubble sources. At the
same time, its influence on strongly oscillating (active) bubbles is less pronounced,
because their Bjerknes force induced motion is often an order of magnitude faster
than the sound field induced liquid motion. The alteration of the sound field by the
bubbles can happen for various reasons. They damp and scatter the sound wave
and thus can cause increased dissipation and shielding. Also the impedance of the
medium can change already for low bubble densities [60] which, for instance, detunes
resonators. The latter effect has been investigated for a special case in Ref. [61], where
the particle code has been coupled to a continuous model of sound propagation in
bubbly liquid [62,63]. Indeed, a promising way to approach a better and universal
simulation tool for acoustic cavitation might be a connection of (microscopic) particle
simulation and (macroscopic) sound field and possibly flow field calculation on basis
of continuous descriptions. First steps in this direction have already been taken, as
in Ref. [61], but still many phenomena have to be investigated in more detail, and
much work lies ahead until a comprehensive and satisfactory description of acoustic
cavitation fields is reached.
Acknowledgements
The author thanks all actual and former members of the nonlinear dynamics and cavitation
group of the DPI at Göttingen University. The friendly and stimulating atmosphere at the
institute was a great help in any respect. Special thanks go to Werner Lauterborn, Thomas
Kurz, and Ulrich Parlitz for continuous and strong support, fruitful discussions and pleasant
joint work. I also want to thank specially Dagmar Krefting, Philipp Koch, Jürgen Appel,
Jann Ohle Claussen, Till Nowak, Alexei Moussatov and Bertrand Dubus, because I used
material from shared work in this article. Last but not least I thank the staff of the electrical
and mechanical workshops of the institute for excellent support.
References
[1] H. G. Flynn, ‘Physics of Acoustic Cavitation in Liquids’, in Physical Acoustics Vol.1B,
edited by W. P. Mason (Academic Press, London, 1964), 57–172.
[2] L. D. Rozenberg, High-Intensity Ultrasonic Fields (Plenum Press, New York, 1971).
[3] E. A. Neppiras, ‘Acoustic Cavitation’, Phys. Rep. 61, 159 (1980).
[4] F. R. Young, Cavitation (McGraw-Hill, London, 1989).
[5] T. G. Leighton, The Acoustic Bubble (Academic Press, London, 1994).
[6] C. E. Brennen, Cavitation and Bubble Dynamics (Oxford University Press, New York,
1995).
[7] W. Lauterborn, T. Kurz, R. Geisler, D. Kröninger, and D. Schanz, ‘The single bubble