Molekulardynamische Untersuchungen zur Binnendynamik kollabierender Blasen

Abstract

This work deals with the numerical simulation of cavitation- and sonoluminescence-bubbles, as well as laser-induced bubbles. The interior of the bubble is simulated by molecular dynamic methods, while the surrounding water is considered to be a continuum. The oscillation of the bubble is modeled via an enhanced Rayleigh-Plesset-equation. The composition is presumend to be a mixture of water vapor and noble gases. The noble gases remain in the bubble, while water vapor is able to condensate or evaporate at the bubble wall. The part of the water vapor that is trapped in the bubble during the fast collapse is mainly dissociated, the generated radicals are chemically active and form new species.At first, the influence of various simulation parameters - e.g. the particle number, or the interaction of the particles with the bubble wall - on the results of the calculation is analysed. This is done on a bubble with model parameters typical for single-bubble-sonoluminescence (SBSL). For the same type of bubbles, the influence of water temperature, excitation pressure and the used noble gas on the achieved temperatures, the creation of different species (chemical yields) and the emitted light energy, is presented. In the following, the model is applied to very small bubbles, that are excited by very high pressures and frequencies. Bubbles of this kind can occour in luminescing cavitation clouds (multi-bubble-sonoluminescence, MBSL). Finally, simulations of laser-induced bubbles are presented. For these, it is presumed, that no noble gas is present and they consist entirely of (partly dissociated) water vapor. The dynamics of the bubble wall, chemical yields and the reached temperatures are analysed for cases where the bubble medium is at rest, as well as cases where the bubble medium is excited by an ultrasonic wave.