arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2003.08071physics.flu-dyn
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两流体非均匀混合的局域波数模型

Local Wave Number Model for Inhomogeneous Two-Fluid Mixing

Nairita Pal, Ismael Boureima, Noah Braun, Susan Kurien, Praveen Ramaprabhu, Andrew Lawrie

摘要:

本文研究了两点谱湍流模型(局域波数模型或LWN模型)的瑞利-泰勒(RT)不稳定性。模型结果进行了比较,从三维模拟RT问题提取的统计量。这些模拟初始化与高波数扰动的界面处的重流体放置在顶部的轻流体,使得密度梯度是在相反的方向上的加速度,由于重力。我们认为低到中等密度对比度的流动,并比较LWN模型对模拟数据使用的混合宽度演变作为主要指标。最初的模型指定物理上合理的,但主要是\emph{ad hoc}的条款,以考虑到不均匀的机制,参与增长的混合层。我们系统地评估的LWN模型方程中的每一个条款的作用,通过与模拟比较。其中两个,运动学源项,引入以保持密度和特定体积之间的有限协方差,和频谱失真项,引入作为密度特定体积协方差的频谱修改,都导致严重过度预测的混合层增长。一个简化的模型,消除这两个方面,以提高捕获的混合宽度的演变,以及在不同的时间跨越混合层的湍流质量通量速度分布。然而,这种简化揭示了对其他度量的保真度,例如密度比体积协方差和湍流动能在某种程度上受到损害。这一结果的影响进行了讨论相对于RT问题的物理,我们提供了这样一个模型的实际使用的指导这项研究。

英文摘要:

We present a study of a two-point spectral turbulence model (Local Wave-Number model or LWN model) for the Rayleigh-Taylor (RT) instability. The model outcomes are compared with statistical quantities extracted from three-dimensional simulation of the RT problem. These simulations are initialized with high wavenumber perturbations at the interface of a heavy fluid placed on top of a light fluid so that the density gradient is in the direction opposite to acceleration due to gravity. We consider flows of low to medium density contrast and compare the LWN model against simulation data using the mix-width evolution as the primary metric. The original model specified physically reasonable but largely \emph{ad hoc} terms to account for the inhomogeneous mechanisms involved in growing the mixing layer. We systematically assess the role of each of the terms in the LWN model equations by comparison with simulation. Two of these, the kinematic source term, introduced to maintain a finite covariance between density and specific volume, and a spectral distortion term, introduced as spectral modifications of the density-specific-volume covariance, both result in severely over-predicting the mix layer growth. A simplified model eliminating those two terms is shown to improve the capture of both mix-width evolution as well as the turbulent mass flux velocity profiles across the mix layer at different times. However, this simplification reveals that fidelity to other metrics such as the density-specific-volume covariance, and the turbulent kinetic energy are somewhat compromised. The implications of this outcome are discussed with respect to the physics of the RT problem, and we provide this study as a guide for the practical use of such a model.

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