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.

介观研究旨在通过两个弛豫时间晶格玻尔兹曼方法研究滑移和过渡状态下收缩纳米通道内部的稀薄气流。拐点处的Bosanquet型有效粘度和分布函数校正用于提高壁面滑移速度的精度。假定纳米通道入口和出口部分的边界条件为非平衡-平衡分布函数。墙的外部考虑了反射后镜面反射的边界条件。研究发现，动量和稀疏度都对纳米通道流中的分离现象起着至关重要的作用。出口努数越多，有效粘度和剪切应力就越高，而涡旋会变小，并在较高的努森数下趋于消失。直接模拟蒙特卡罗方法的结果已被用于验证当前的数值预测，并且结果之间显示出突出的一致性。