
Simulation of natural convection under high magnetic field by means of the thermal lattice Boltzmann method
Zhong ChengWen(钟诚文), Xie JianFei(解建飞), Zhuo CongShan(卓从山), Xiong ShengWei(熊生伟), and Yin DaChuan(尹大川)
Chin. Phys. B, 2009, 18 (10):
40834093.
DOI: 10.1088/16741056/18/10/004
The thermal lattice Boltzmann method (TLBM), which was proposed by J. G. M. Eggels and J. A. Somers previously, has been improved in this paper. The improved method has introduced a new equilibrium solution for the temperature distribution function on the assumption that flow is incompressible, and it can correct the effect of compressibility on the macroscopic temperature computed. Compared to the previous method, where the halfway bounce back boundary condition was used for nonslip velocity and temperature, a nonequilibrium extrapolation scheme has been adopted for both velocity and temperature boundary conditions in this paper. Its secondorder accuracy coincides with the ensemble accuracy of lattice Boltzmann method. In order to validate the improved thermal scheme, the natural convection of air in a square cavity is simulated by using this method. The results obtained in the simulation agree very well with the data of other numerical methods and benchmark data. It is indicated that the improved TLBM is also successful for the simulations of nonisothermal flows. Moreover, this thermal scheme can be applied to simulate the natural convection in a nonuniform high magnetic field. The simulation has been completed in a square cavity filled with the aqueous solutions of KCl (11wt%), which is considered as a diamagnetic fluid with electrically lowconducting, with Grashof number Gr=4.64×10^{4} and Prandtl number Pr=7.0. And three cases, with different cavity locations in the magnetic field, have been studied. In the presence of a high magnetic field, the natural convection is quenched by the body forces exerted on the electrically lowconducting fluids, such as the magnetization force and the Lorentz force. From the results obtained, it can be seen that the quenching efficiencies decrease with the variation of location from left, symmetrical line, to the right. These phenomena originate from the different distributions of the magnetic field strengths in the zones of the symmetrical central line of the magnetic fields. The results are also compared with those without a magnetic field. Finally, we can conclude that the improved TLBM will enable effective simulation of the natural convection under a high magnetic field.
