Entropy generation rates in two-dimensional Rayleigh-Taylor (RT) turbulence mixing are investigated by numerical calculation. We mainly focus on the behavior of thermal entropy generation and viscous entropy generation of global quantities with time evolution in Rayleigh-Taylor turbulence mixing. Our results mainly indicate that, with time evolution, the intense viscous entropy generation rate s u and the intense thermal entropy generation rate S θ occur in the large gradient of velocity and interfaces between hot and cold fluids in the RT mixing process. Furthermore, it is also noted that the mixed changing gradient of two quantities from the center of the region to both sides decrease as time evolves, and that the viscous entropy generation rate 〈 S u 〉 V and thermal entropy generation rate 〈 S θ 〉 V constantly increase with time evolution; the thermal entropy generation rate 〈 S θ 〉 V with time evolution always dominates in the entropy generation of the RT mixing region. It is further found that a "smooth" function 〈 S u 〉 V ∼ t 1 / 2 and a linear function 〈 S θ 〉 V ∼ t are achieved in the spatial averaging entropy generation of RT mixing process, respectively.
Keywords: Rayleigh–Taylor; entropy; lattice Boltzmann method; mixing; turbulence.