Instability of sonoluminescing bubbles under a nonspherical symmetrical acoustic-pressure perturbation

Dynamics of two interacting bubbles in a nonspherical ultrasound field

In this paper, we present and analyze a model of the oscillations of a pair of gas bubbles driven by nonspherical ultrasound. We derived our model based on the perturbation and potential flow theories and use it to study three cases of oscillation of two bubbles under driving ultrasound with different initial phases, different separation distances between the bubbles and different sound pressure amplitudes. For the driving ultrasound with different initial phases, we obtain the in-phase and anti-phase radial pulsations of the bubbles in incompressible liquid. We also study the effect of the secondary Bjerknes force on the oscillation of bubbles separated by different relative distances. Lastly, we analyze the ratio of a nonspherical to a spherical partial quantity, and the results show that the bubbles survive longer with decreases in both the pressure amplitude of nonspherical ultrasound and the initial bubbles radii.

Saturation of shape instabilities in single-bubble sonoluminescence

Excitation of shape instabilities represents one route to bubble death in single-bubble sonoluminescence. This feature is satisfactorily explained by an expansion to first order in the amplitude of a shape distortion in the form of a spherical harmonic. By taking the expansion to second order, it is found that regions of parameter space exist where the exponential growth into bubble disruption is checked and a saturated stable state of shape distortion is possible. Experimental evidence provided by Mie scattering is presented, and a possible connection to simultaneous spatially anisotropic light emission is discussed.

Instability of a bubble chain

Based on the theory of shape instability and diffusive instability for single bubbles, we have studied the instability of an individual bubble in a bubble chain and found that its stable area enlarges the narrower the distance between bubbles. The spatial stability of the bubble chain is due to the secondary Bjerknes force between bubbles. Numerical calculations show the tension of the bubble chain varies with bubble distance and maxima appear at certain distances which could correspond to the stable states of the bubble chain.

Temperature and intensity of sonoluminescence radiation in sulfuric acid

The spectral radiation of sonoluminescence (SL) from sulfuric acid doped with various Xe concentrations has been studied in a hydrochemical simulation, including radiation effects of both continuum and line emissions. The simulation considers the same temperature for both continuum and line parts of the SL spectrum and gives results in agreement with the experiment. Also, it can properly show period-doubling dynamics for a 50 torr bubble. For most of the allowable driving pressures, it is shown that both the temperature and the intensity of SL for a 4 torr bubble are greater than those of a 50 torr bubble. However, for the range of pressures near the maximum driving conditions of the 50 torr bubble, the SL intensity of this bubble can be up to three orders of magnitude greater than the 4 torr bubble. This case, which is in agreement with the experiment, is obtained when the light-emitting region of the 50 torr bubble is about three orders of magnitude greater than the 4 torr bubble.

Influence of liquid density on the parametric shape instability of sonoluminescence bubbles in water and sulfuric acid

Parametric shape instability of sonoluminescing argon bubbles in water and aqueous H(2)SO(4) was numerically analyzed considering gas and liquid density variations. The employed model couples Gilmore, Tait (liquid) and van der Waals (gas) equations to simulate radial dynamics and density changes, respectively. Shape stability-instability zones in the P(a)-R(0) space resulted from a linear stability analysis. For the argon-water and argon-water-acid systems, numerical results indicate a rapid rise in both gas and liquid densities during final stages of bubble implosion which result in a stabilizing effect on the parametric instability.

Experimental study of transient paths to the extinction in sonoluminescence

An experimental study of the extinction threshold of single bubble sonoluminescence in an air-water system is presented. Different runs from 5% to 100% of air concentrations were performed at room pressure and temperature. The intensity of sonoluminescence (SL) and time of collapse (t(c)) with respect to the driving were measured while the acoustic pressure was linearly increased from the onset of SL until the bubble extinction. The experimental data were compared with theoretical predictions for shape and position instability thresholds. It was found that the extinction of the bubble is determined by different mechanisms depending on the air concentration. For concentrations greater than approximately 30%-40% with respect to the saturation, the parametric instability limits the maximum value of R(0) that can be reached. On the other hand, for lower concentrations, the extinction appears as a limitation in the time of collapse. Two different mechanisms emerge in this range, i.e., the Bjerknes force and the Rayleigh-Taylor instability. The bubble acoustic emission produces backreaction on the bubble itself. This effect occurs in both mechanisms and is essential for the correct prediction of the extinction threshold in the case of low air dissolved concentration.

Surface-wave instabilities, period doubling, and an approximate universal boundary of bubble stability at the upper threshold of sonoluminescence

Numerical results are presented for hydrodynamic instabilities surrounding the parameter space of sonoluminescing bubbles. The Rayleigh-Taylor instability is shown to limit bubble oscillations only in a small region near a border at small radii in noisy environments. Also, two different noise-induced instabilities by secondary collapses are identified. The reason for period-doubled, anisotropic emission is found to be the coupling of radial and surface oscillations. Furthermore, an approximate universal border is shown to exist above which the bubble is destroyed by the parametric instability. The results are compared to experimental results from several publications using different experimental setups.