耦合宏观/介观方法的振荡热驱稀薄流动
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国防科技大学空天科学学院

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O354

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国家自然科学基金(12302382,12372297);湖南省自然科学基金青年基金项目(2022JJ40542)


Hybrid macro-/mesoscopic scheme for thermally-induced oscillatory rarefied gas flows
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    摘要:

    对二维方腔中顶盖温度振荡驱动稀薄流动进行研究,分析努森数Kn与顶盖温度振荡频率St对流场参数的影响规律。在靠近壁面处基于介观尺度离散速度法与Maxwell壁面边界条件求解Shakhov模型方程,精确捕获壁面位置处强非平衡效应,远离壁面处基于宏观尺度R26矩方法减小计算资源消耗。宏观/介观虚拟边界利用高阶Hermite多项式重构分布函数,以封闭数值迭代格式。仿真结果表明:耦合方法相较全流场介观尺度方法,对方腔垂直中线处温度的预测结果相符,最大计算误差为0.23%,计算内存消耗降低约69.91%。同时,耦合方法能够捕获振荡热驱稀薄流动在大Kn数流域的非线性现象,此时水平方向速度分布不再服从周期振荡余弦函数规律,且上升时间远大于下降时间。粘性穿透层厚度与受扰区域随着Kn数的增大而增大,随着St数的增大而减少。

    Abstract:

    Thermally-induced oscillatory rarefied gas flow inside a two-dimensional rectangular cavity is investigated. The effects of the Knudsen numbers and the oscillation frequency of lid temperature on the flow parameters are analyzed. A discrete velocity method, combined with Maxwell’s wall boundary condition, is employed to solve the Shakhov model equation numerically in the near-wall region. Hence, strong non-equilibrium effects can be captured accurately at the mesoscopic level. At the macroscopic level, the R26 moment method is adopted in the bulk flow region to reduce the computational cost. To close the numerical iteration procedure, the velocity distribution functions, serve as the pseudo boundary between macroscopic and mesoscopic methods, are reconstructed using the high-order Hermite polynomials. Numerical simulations demonstrate that the temperature profile at the central vertical of the cavity predicted by the hybrid method are in good agreement with results from the mesoscopic method, with maximum error 0.23%. Besides, the computational memory cost can be saved up to about 69.91%. Furthermore, the hybrid approach is able to capture the nonlinear phenomenon in the thermally-induced oscillatory rarefied gas flow under high Kn numbers, where the horizontal velocity no longer obeys the law of periodic oscillating cosine function, and the rise time of the horizontal velocity is much longer than the fall time. The thickness of the viscous penetration layer and the disturbed region increases as the Kn number increases, and decreases as the St number increases.

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  • 收稿日期:2023-09-24
  • 最后修改日期:2025-09-02
  • 录用日期:2024-01-23
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