Simulation of axisymmetric free surface viscous flow around a non-spherical bubble in the sonoluminescence regime
Résumé
When excited with ultrasound waves, air bubbles in water can, in appropriate con
ditions, emit light. This phenomenon is known as {\em sonoluminescence}.
While recent experiments have successfully produced stable single bubble sonolum
inescence, allowing the conditions for sonoluminescence to be studied in more de
tail, the mechanism for light emission remains little understood.
The classical explanation relies
on a shock wave theory \cite{crum94}\cite{greenspan93}. These authors suggest th
at during the violent collapse of
the bubble, spherical shock waves are emitted which concentrate on a
singular point at the center of the bubble yielding very high temperatures
($>$ 10,000 {\kelvin}) and very short light pulses ($\approx$ 50 picoseconds)\ci
te{barber91}. However,
this hypothesis has serious weak points underlined by A. Prosperetti \cite{prosp
eretti97}. The main
assumption of the shock wave hypothesis is that the bubble remains
spherical throughout the pressure cycle. There is strong evidence that the
bubble should deform strongly when reaching very small radii.
In particular a jet of liquid should form in the direction of the
bubble motion. If
this is the case, the shock wave model does not hold
anymore (at least in its present form) and another mechanism for light
emission should be found.
Our goal is to illustrate numerically the
possibility of stable and repeatable formation of a jet at each
sonoluminescence cycle. While some boundary-integral computations have been
made \cite{prosperetti97}, we are not aware of a full Navier-Stokes simulation o
f such a
phenomenon.
The phenomenon of jet formation is moreover a characteristic of cavitation bubbl
es near solid walls. Sonoluminescence and cavitation thus appear to be closely r
elated \cite{Lauterborn97}.
We will present a free-surface Navier-Stokes solver which can be useful for the
study of these two phenomena and some results regarding both cavitation and sono
luminescence.
Origine : Fichiers produits par l'(les) auteur(s)
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