稀化泊肃叶流动中的跨流压力支撑与标量松弛极限
Cross-stream pressure support and the limits of scalar relaxation in rarefied Poiseuille flow
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中文总结 AI 辅助
该研究针对稀化泊肃叶流动，分析了压力驱动下弱壁法向压力变化的机制，通过DSMC模拟与NCCR模型，揭示了应力与动量补偿对压力振幅的影响，指出弱非平衡可观测量的一致性不代表内部闭合机制正确。
中文摘要 AI 辅助
压力驱动的稀化泊肃叶流动中弱壁法向压力变化是对高阶本构模型的严格测试：它在总压力范数中几乎不可见，却由各向异性分子应力产生。切向形式的非线性耦合本构关系（NCCR）可重现其凸拓扑，但其定量成功的物理原因仍未明确。我们探究本构应力关系与简化流向驱动是各自独立准确，还是二者效果相互补偿。对直接模拟蒙特卡洛（DSMC）模拟结果的分析采用了二维动量收支、基于横向信号的压力误差范数、匹配出口克努森数（Knudsen）对比以及预消去NCCR平衡的分量测试。非平衡壁法向应力过度支撑了测得的压力缺陷，而剪切应力的流向输运提供了相反的修正。状态图、动量收支与驱动诊断显示，出口克努森数或出口马赫数均无法单独组织压力振幅；在固定比率序列中，稀化伴随本构诊断的变化大于压力振幅的变化。DSMC推断的应力关系偏离了固定简化系数，即使是最佳通用标量，对主导剪切分量的闭合也远比对承载压力场的法向分量准确。因此，仅修正系数会恶化重构，而恢复被省略的流向动量项可降低强加速情况下的振幅偏差。简化定律可通过应力-动量补偿保持准确，表明弱非平衡可观测量的一致性未必意味着内部闭合机制正确。
英文摘要
The weak wall-normal pressure variation in pressure-driven rarefied Poiseuille flow is a stringent test of higher-order constitutive models: it is almost invisible in the total-pressure norm, yet it is generated by anisotropic molecular stress. A tangent-form nonlinear coupled constitutive relation (NCCR) reproduces its convex topology, but the physical reason for its quantitative success remains unresolved. We ask whether the constitutive stress relation and reduced streamwise forcing are independently accurate or whether their effects compensate. A direct simulation Monte Carlo (DSMC) campaign is analysed using two-dimensional momentum budgets, a pressure-error norm based on the transverse signal, a matched-outlet-Knudsen comparison and componentwise tests of the pre-elimination NCCR balance. The non-equilibrium wall-normal stress over-supports the measured pressure defect, while streamwise transport of shear stress supplies an opposing correction. The state map, momentum budgets and forcing diagnostics show that neither outlet Knudsen nor outlet Mach number alone organises the pressure amplitude; along the fixed-ratio sequence, rarefaction is accompanied by larger changes in the constitutive diagnostics than in pressure amplitude. The DSMC-inferred stress relation departs from the fixed reduced coefficient, and even the best common scalar closes the dominant shear component far more accurately than the normal components that carry the pressure field. Correcting the coefficient alone can therefore worsen the reconstruction, whereas restoring omitted streamwise-momentum terms reduces the amplitude bias in strongly accelerated cases. The reduced law can remain accurate through stress--momentum compensation, showing that agreement of a weak non-equilibrium observable need not imply correct internal closure mechanics.
