Sudden contraction effects in nanochannel cross section on the rarefied gas flow characteristics: LBM analysis

Abstract

This mesoscopic investigation aims to study the rarefied gas flow inside a contracting nanochannel in the slip and transitional regimes by two relaxation time lattice Boltzmann method. Bosanquet-type effective viscosity and distribution functions correction at the corner points are used to enhance the precision of slippage velocity on the walls. The boundary conditions at the entrance and exit sections of the nanochannel are assumed nonequilibrium-equilibrium distribution functions. The bounce back-specular reflection boundary conditions are considered for the wall exteriors. It is found that both momentum and rarefaction play essential roles concerning the separation phenomena in nanochannel flow. The higher outlet Knudsen number possesses the higher effective viscosity and shear stress, while the vortices become smaller and tend to disappear at higher Knudsen numbers. The results of the direct simulation Monte Carlo method have been utilized to validate the present numerical prediction, and an outstanding agreement between the results is shown.