We provide the first direct calculation of the Knudsen layer (KL) thickness in rarefied gas flows based on the ballistic molecular motions in the direct simulation Monte Carlo simulations. Calculations reproduce a linear relation between the KL thickness and the mean free path (MFP) of the gas, which agrees with the classical gas kinetic theory statement. The ratio of the KL thickness and MFP is only a function of the gas molecular model at slight flow gradients. However, high flow gradient and high surface curvature effects destroy the linear relation between the KL thickness and MFP.

中文翻译：

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稀薄气流中 Knudsen 层厚度的广义描述

我们基于直接模拟 Monte Carlo 模拟中的弹道分子运动，首次直接计算稀薄气流中的 Knudsen 层 (KL) 厚度。计算再现了 KL 厚度和气体的平均自由程 (MFP) 之间的线性关系，这与经典的气体动力学理论陈述一致。KL 厚度和 MFP 的比率只是气体分子模型在轻微流动梯度下的函数。然而，高流动梯度和高表面曲率效应破坏了 KL 厚度和 MFP 之间的线性关系。