分子波动抑制压缩湍流中的间歇性
Molecular Fluctuations Inhibit Intermittency in Compressible Turbulence
AI总结：
分子波动抑制压缩湍流中的间歇性，改变化了耗散范围内的湍流统计特性。
摘要：
在标准的完全发展湍流图景中，高度间歇性的流体场通过尺度非线性耦合，其中局部能量从大尺度 cascade 到耗散涡旋和大密度梯度。然而，微观上，构成流体的分子处于持续的热（布朗）运动中，但分子波动对大尺度湍流的作用尚不明确，历史上在大于分子平均自由程的尺度上通常被认为无关。最近的理论和计算研究显示，分子波动可以在 Kolmogorov 尺寸上影响能量 cascade。本文显示，分子波动不仅在 Kolmogorov 尺寸以上的波长上修改能量谱，在整个耗散范围内显著抑制时空间歇性。利用大规模直接数值模拟计算波动流体动力学，我们证明了湍流模型中极端间歇性特征被替换成近高斯统计。这些结果表明，压缩 Navier-Stokes 方程应加入分子波动以准确预测耗散范围内的湍流统计。我们的发现对天体物理、反应流和高超声速空气动力学等应用中的湍流建模有重大影响，其中耗散范围的湍流通过闭合模型近似。
英文摘要：
In the standard picture of fully-developed turbulence, highly intermittent hydrodynamic fields are nonlinearly coupled across scales, where local energy cascades from large scales into dissipative vortices and large density gradients. Microscopically, however, constituent fluid molecules are in constant thermal (Brownian) motion, but the role of molecular fluctuations on large-scale turbulence is largely unknown, and with rare exceptions, it has historically been considered irrelevant at scales larger than the molecular mean free path. Recent theoretical and computational investigations have shown that molecular fluctuations can impact energy cascade at Kolmogorov length scales. Here we show that molecular fluctuations not only modify energy spectrum at wavelengths larger than the Kolmogorov length in compressible turbulence, but they also significantly inhibit spatio-temporal intermittency across the entire dissipation range. Using large-scale direct numerical simulations of computational fluctuating hydrodynamics, we demonstrate that the extreme intermittency characteristic of turbulence models is replaced by nearly-Gaussian statistics in the dissipation range. These results demonstrate that the compressible Navier-Stokes equations should be augmented with molecular fluctuations to accurately predict turbulence statistics across the dissipation range. Our findings have significant consequences for turbulence modeling in applications such as astrophysics, reactive flows, and hypersonic aerodynamics, where dissipation-range turbulence is approximated by closure models.
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