Effects of isothermal-adiabatic boundary conditions on the transition characteristics in two-dimensional turbulent Rayleigh–Bénard convection

Abstract

In this article, two-dimensional (2-D) Rayleigh–Bénard (RB) convection with isothermal-adiabatic boundary conditions is simulated by using the double distribution function approach of lattice Boltzmann method. The effects of isothermal-adiabatic boundary on the flow and the heat transfer characteristics in the RB system under instability, transition and turbulence are discussed in detail. The effect of the isothermal-adiabatic boundary on the scaling of Nusselt (Nu) number as a function of Rayleigh (Ra) number is analyzed. The 0.3 scaling is observed in the mixed boundary system when the Ra number is in the range of 107–108. The scaling is well consistent with that in the RB system with uniform boundaries. A comparison of the influence on the root mean square of Nu number between uniform isothermal boundary and isothermal-adiabatic boundary demonstrates that in both “transition” region and “turbulence” region, the intensity of the fluctuation of average Nu number at uniform isothermal boundary is higher than that at the isothermal-adiabatic boundary. The comparison of the fluctuation of the average Nu number between “transition” region and “turbulence” region shows that the isothermal-adiabatic boundary has a better suppression effect on the fluctuation of heat transfer in the “transition” region. The supression is related to ratio of the scale of plume and the “heat source core.” When the scales are comparable, the fluctuation of average Nu number will be significantly suppressed. Flow field and temperature field further show the plumes are generated at these “heat source cores,” which effectively supports the “heat source core” assumption.