Baochang Shi

An extrapolation method for boundary conditions in lattice Boltzmann method

A boundary treatment for curved walls in lattice Boltzmann method is proposed. The distribution function at a wall node who has a link across the physical boundary is decomposed into its equilibrium and nonequilibrium parts. The equilibrium part is then approximated with a fictitious one where the boundary condition is enforced, and the nonequilibrium part is approximated using a first-order extrapolation based on the nonequilibrium part of the distribution on the neighboring fluid node. Numerical results show that the present treatment is of second-order accuracy, and has well-behaved stability characteristics.

Lattice Boltzmann simulation of surface roughness effect on gaseous flow in a microchannel

At the microscale level, it is impossible to obtain a completely smooth wall surface, and the effect of surface roughness may be a main factor responsible for some different characteristics between fluid flow in the microchannels and that in conventional size channels. In the present work, the lattice Boltzmann method is applied to investigate the gaseous flow in a microchannel with surface roughness which is modeled by an array of rectangular modules. The effects of relative surface roughness, roughness distribution, and rarefaction on gaseous flow are studied, but the compressibility effect is neglected since the Mach number is less than 0.2. It was shown that the surface roughness had an important influence on friction factor and mass flow rate. In particular, this effect becomes more significant with the decrease of the Knudsen number. This is because the rarefaction reduces the interaction between the gas molecules and the channel walls, which results in reduction of the surface roughness effect.