Rayleigh-Benard type natural convection heat transfer in two-dimensional geometries

摘要

The natural convection of Rayleigh-Benard type for various Rayleigh numbers, in two-dimensional L shape and diagonally flipped-L shape enclosures is studied using multiple relaxation time (MRT) based lattice Boltzmann method (LBM). Two separate particle distribution functions (i.e. the use of double distribution functions (DDF) approach) are employed to obtain the flow- and temperature-fields. The variables are intrinsically coupled by considering the effect of density difference in the buoyancy term and neglecting the viscous heat dissipation and compression work due to pressure. The benchmark simulations are first performed for differentially heated square enclosure to ascertain the correctness of in-house build code. Then, simulations are carried out for L shape and diagonally flipped-L shape 2D enclosures by varying Rayleigh number from 10(3) to 10(8). The steady Rayleigh-Benard convection (RBC) is observed for both the enclosures at low Rayleigh numbers (i.e. Ra = 10(3), 10(4) and 10(5)). However, for higher Rayleigh numbers, unsteadiness in the flow-structure is observed. This unsteady behavior of the flow is then characterized by using time-dependency signal of spatially averaged Nusselt number on the hot wall and its corresponding frequency analysis.