Role of liquid compressional viscosity in the dynamics of a sonoluminescing bubble.

The well-known Rayleigh-Plesset ( RP ) equation is the basis of almost all hydrodynamical descriptions of single-bubble sonoluminescence ( SBSL ). A major deficiency of the RP equation is that it accounts for viscosity of an incompressible liquid and compressibility, separately. By removing this approximation, a new modification of the RP equation is presented considering effect of compressional viscosity of the liquid. This modification leads to addition of a new viscous term to the traditional bubble boundary equation. Influence of this new term in the dynamics of a sonoluminescing bubble has numerically been studied considering effects of heat transfer at the bubble wall, nonequilibrium evaporation and condensation of water vapor, chemical reactions, and diffusion of the reactions products in the liquid. The results show that the new term has a significant damping role in the bubble motion at the end of collapse and during the rebounds, so that its consideration dramatically reduces amplitude of the afterbounces. Dependence of this new damping mechanism on the driving pressure amplitude and on the ambient radius has been investigated. The results indicate that the more intense the collapse, the more important the damping of the liquid compressional viscosity.