Surface tension effects on Rayleigh-Taylor instability in nonideal fluids: A multiple-relaxation-time discrete Boltzmann study

A multi-relaxation-time discrete Boltzmann model for compressible non-ideal gases with adjustable specific heat ratio is proposed, and the impact of surface tension on Rayleigh-Taylor instability (RTI) is investigated from two perspectives: macroscopic and non-equilibrium characteristics. In terms of physical cognition, (1) it is found that there are two critical surface tensions: the upper critical value and the lower critical value. When the surface tension is below the lower critical value, the RTI evolution aligns qualitatively with the case without surface tension. As the surface tension coefficient increases, the inhibitory effect on RTI evolution gradually strengthens. When the surface tension is greater than the upper critical value, the disturbance interface tends to be stable after multiple oscillations. When the surface tension is in between, the perturbation interface first reverses, or even multiple reverses, and then destabilizes and develops rapidly. (2) A series of new kinetic behavior characteristics are given, and it is found that some behavior characteristics have important reference value for the control of system behavior. For example, the first peak in the growth rate of the global average non-organized momentum flux strength D₂ corresponds to the onset of the regular nonlinear stage. The peak in the growth rate of the global average non-organized energy flux strength D_3,1 marks the beginning of the re-acceleration stage. The onset of the uniform acceleration stage in the growth rate of the global average non-equilibrium strength D_TNE corresponds to the system transitioning into the regular nonlinear stage, while its terminal point (also the peak) corresponds to the system entering the re-acceleration stage. These insights enhance understanding of RTI mechanisms in complex fluids kinetically.