Accuracy of the lattice Boltzmann method for low-speed noncontinuum flows

Simulation of noncontinuum gas flows presents tremendous challenges, especially for nanoscale devices that usually exhibit low speeds and isothermal conditions. Such simulations are often achieved through use of the Boltzmann Bhatnagar-Gross-Krook equation, which forms the foundation for the lattice Boltzmann (LB) method. Accuracy of the LB method in noncontinuum flows is widely assumed to depend on the order of quadrature used. Here, we study noncontinuum Couette flow and discover that interaction of the lattice with the solid boundaries is the dominant mechanism controlling accuracy--quadrature order plays a comparatively minor role. This suggests the applicability of low-order quadrature in LB simulation of wall bounded isothermal noncontinuum flows, and leads to a framework and rationale for accurate implementation of LB models in noncontinuum flows.