Extreme-value statistics from Lagrangian convex hull analysis for homogeneous turbulent Boussinesq convection and MHD convection
Extreme-value statistics from Lagrangian convex hull analysis for homogeneous turbulent Boussinesq convection and MHD convection
复制标题
均匀湍流 Boussinesq 对流和 MHD 对流的拉格朗日凸包分析的极值统计
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
S. Chapman
中科院分区：
文献类型：
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作者：
J. Pratt;A. Busse;Wolf;N. Watkins;S. Chapman;S. Chapman;S. Chapman
本文研究了拉格朗日示踪剂的凸船体在不同各向异性湍流输运特性分析中的应用。在统计均匀和稳态Navier-Stokes湍流，中性流体Boussinesq对流，MHD Boussinesq对流的直接数值模拟与拉格朗日对色散的比较表明，凸船体统计捕获的渐近色散行为的一大群被动示踪粒子。此外，凸包船体分析提供了关于示踪剂子系综的附加信息，这些示踪剂平均以极值统计和流动各向异性的形式经由凸包的几何性质最有效地分散。我们使用凸船体表面的几何形状来研究湍流对流中发生的各向异性。应用极值理论，我们证明了凸船体顶点的最大平方扩张是由一个经典的极值分布，Gumbel分布很好地描述。在湍流对流期间，间歇性对流羽流增长并加速拉格朗日示踪剂的分散。凸船体分析产生的信息补充了相干湍流结构的标准拉格朗日分析及其对流的全局统计的影响。
We investigate the utility of the convex hull of many Lagrangian tracers to analyze transport properties of turbulent flows with different anisotropy. In direct numerical simulations of statistically homogeneous and stationary Navier–Stokes turbulence, neutral fluid Boussinesq convection, and MHD Boussinesq convection a comparison with Lagrangian pair dispersion shows that convex hull statistics capture the asymptotic dispersive behavior of a large group of passive tracer particles. Moreover, convex hull analysis provides additional information on the sub-ensemble of tracers that on average disperse most efficiently in the form of extreme value statistics and flow anisotropy via the geometric properties of the convex hulls. We use the convex hull surface geometry to examine the anisotropy that occurs in turbulent convection. Applying extreme value theory, we show that the maximal square extensions of convex hull vertices are well described by a classic extreme value distribution, the Gumbel distribution. During turbulent convection, intermittent convective plumes grow and accelerate the dispersion of Lagrangian tracers. Convex hull analysis yields information that supplements standard Lagrangian analysis of coherent turbulent structures and their influence on the global statistics of the flow.