Simulations of natural convection heat transfer in an enclosure at different Rayleigh number using lattice Boltzmann method

• Dimensionless distance of heated source strongly affects the turbulent intensity.
• Flow still keeps soft turbulent convection at dimensionless distance of 0.2 and Ra=108.
• Flow in cavity becomes fully turbulent natural convection at Ra=109.
• Core region scaling seems to approach the behavior of a passive scalar as Ra increases.

Natural convection heat transfer of air for turbulent flow in cavity is investigated using the lattice Boltzmann method (LBM). This study appraises existing scaling laws in previous studies and covers a range of Rayleigh number (Ra) between 105 and 109. It is found that the comparison of the results at low Ra excellently agrees with the results from the literature. The dimensionless distance of heated source in cavity is one of the important factors. The results also explain the mechanism of natural convection rate increasing with the Ra. When the dimensionless length of heat source is equal to 1/5 at Ra of 108, the flow in the enclosure still keeps soft turbulent convection. The flow in cavity becomes fully turbulent natural convection at Ra=109. The core region scaling seems to approach the behavior of a passive scalar as Ra increases, i.e. it changes from pure exponential to a stretched exponential scaling. It is noticed that the results obtained from the present LBM simulations are in good agreement with the Kolmogorov-law and Bolgiano-law.