Validation of a Second-Order Slip Model for Dilute Gas Flows
Validation of a Second-Order Slip Model for Dilute Gas Flows
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稀气流二阶滑移模型的验证
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
N. Hadjiconstantinou
中科院分区：
文献类型：
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作者：
N. Hadjiconstantinou
我们给出了硬球气体的直接蒙特卡罗模拟与最近提出的二阶滑移模型耦合的Navier-Stokes描述的预测之间的广泛比较。考虑了两个一维、时间相关的通道流。在这两种情况下，分子模拟和所提出的模型都很好地符合速度场和应力场的过渡区域。极好的定量一致性大约扩展到基于0.4的通道宽度的克努森数。流动的瞬变性质表明，尽管滑移模型的起源是(准)稳定的，但只要与分子碰撞时间相比，演化时间标度较长，它仍然是可靠的。我们的讨论阐明了Knudsen层的影响，Knudsen层是壁面附近的一个动力学“边界层”，需要叠加到流动的Navier-Stokes分量上才能获得完整的流动解。这种运动边界层的存在，其重要性随着努森数的增加而增加，最终导致Navier-Stokes分量不足以描述流动，这意味着在解释滑移流场时需要特别注意。
We present an extensive comparison between direct Monte Carlo simulations and the predictions of the Navier-Stokes description coupled to a recently proposed second-order slip model for hard sphere gases. Two one-dimensional, time-dependent channel flows are considered. In both cases excellent agreement is found between molecular simulation and the proposed model well into the transition regime for both the velocity and stress fields. The excellent quantitative agreement extends, approximately, to a Knudsen number based on the channel width of 0.4. The transient nature of the flows suggests that the slip model, despite its (quasi-) steady origins, remains reliable as long as the evolution timescale is long compared to the molecular collision time. Our discussion elucidates the effect of the Knudsen layer, a kinetic “boundary layer” in the vicinity of walls that needs to be superposed to the Navier-Stokes component of the flow in order to obtain the complete flow solution. The existence of this kinetic boundary layer, whose importance grows with increasing Knudsen number and which ultimately renders the Navier-Stokes component insufficient to describe the flow, implies that special care is needed in interpreting slip-flow flowfields.