Research On The Characteristics Of Sonoluminescence And The Instability Of Multi-bubble

One side, we developed a model to simulate the flash in a spherical bubble. Itassumed that a mixture of inert gas and water vapor fills the bubble. Many processeswere considered in the calculation, such as the diffusion and thermal conduction of thegas; the evaporation and condensation of water vapor occurs at the bubble wall; the heatexchange between the gas in the bubble and the surrounding water; chemicaldissociation of hot gases and the ionization of atoms or molecules. Most of theimportant light emission processes in the hot gas are included in the model. Theseprocesses include electron-neutral atom and electron-ion bremsstrahlung, the radiativeattachment of electrons to atoms or molecules, recombination radiation, the emission ofatomic and ionic spectral lines of Na, Ar,O+2and molecular spectral emission of OHradicals near310nm. These processes depend on the local pressure, density andtemperature, which can be calculated by solving the partial differential equations for thefluid mechanics inside the bubble. The boundary is the moving bubble wall, and itsmotion can be described by the bubble dynamics equation. Under this model, we havestudied the effect of slightly different forms of bubble motion equations on thesonoluminescence, the contribution percentage of the spectral lines at differenttemperature and pressure and the abnormal ionization in the sonoluminescencingbubble.The study found that for brighter bubbles, higher temperature and pressure areapproached, and the continuum radiation much overwhelms the spectral line emissionprocesses. That is, the spectral line emission stands for lower temperature and pressurein the sonoluminescencing bubble. In addition, slightly different forms of bubble motionequations had a great influence on the characteristics of sonoluminescence, but had littleimpact on light pulse width. The calculated full width at half maximum of the SBSLpulse for all the He and Ar bubbles are too small compared with the experimental results.Try to make many attempts, such as improving the bubble motion equation or the stateequation of the gas and so on, but they can not markedly improve the result. Accordingto the enlightenment of Putterman’s experiment, we assume that the ionization potentialof the gas molecules declined dramatically. As a result, the ionization degree inside the sonoluminescencing bubbles can reach unexpectedly high level under a not very hightemperature by strongly lowering the ionization potential of the gas, and the calculatedspectrum and light pulse can well agree with the experimental results. It indicates thatthe sonoluminescencing bubbles may have abnormal ionization process when they flash.But with the known theory, the mechanism of reduction in ionization potential is notclear up to now yet.On the other side, cavitation is both a nonlinear and a many-body problem and it isenormously difficult to perform a direct calculation. In the present paper, we considereda simplification where cavitaion bubbles form filamentary structures (i.e. bubble chain)and studied the instability of the bubble chain from three aspects, such as shapeinstability, diffusive instability and spatial instability. We found that the secondaryBjerknes force makes cavitation forming various stable structures. For the bubble chain,there exists a typical d of~1mm that make the chain stable for a given frequency,regardless whether the chain is formed in water or in phosphoric acid, matching with theexperimental observation.