Deciphering surface tension effects of double cavitation bubbles interaction: A lattice Boltzmann study

A modified double distribution function thermal lattice Boltzmann method is employed to study the influences of surface tension on the interaction between two equal-sized and two unequal-sized bubbles. The entire evolution process of the laser- or spark-produced bubble, including the inception, growth and collapse stage, is realised by considering a temperature that is equal to or higher than the critical temperature, and the effects of the flow and temperature fields on each other are also considered. Based on the Rayleigh–Plesset (R–P) equation and considering the effects of the adjacent bubble, a thermal effect term is incorporated, and this modified R–P equation can predict the radius evolution process for the two equal-sized and the two unequal-sized cavitation bubbles while considering the thermal effect. For the strong interaction mode of the two equal-sized cavitation bubbles, the large surface tension prevents the dramatic distortion of the bubbles, leading to an overall movement of the cavitation bubble under the influence of the Bjerknes force and resulting in an easier coalescence, which significantly reduces the interval distance for the strong film mode than that of the small surface tension. However, for the two unequal-sized bubbles, since non-equilibrium force is present on both sides of the liquid film, the small bubble will be pushed away from the symmetry axis, leading to a difficult coalescence, which will consequently decrease the interval distance for the coalescence mode. Furthermore, an external source term is utilized to achieve the tuneable surface tension and an additional stress term is introduced on the pressure tensor as Gc46κψ∇∇ψ; thus, the inertia model can accurately predict the film thinning process with κ=0. Moreover, a modified inertia model is proposed for the thinning process of the film between two unequal-sized bubbles, which was shown to be accurate for κ=0.