Vertically localised equilibrium solutions in large-eddy simulations of homogeneous shear flow
Vertically localised equilibrium solutions in large-eddy simulations of homogeneous shear flow
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均匀剪切流大涡模拟中的垂直局部平衡解
DOI：
10.1017/jfm.2017.450
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发表时间：
2016
影响因子：
3.7
通讯作者：
J. Jiménez
中科院分区：
文献类型：
--
作者：
A. Sekimoto;J. Jiménez
在大涡模拟（LES）中，没有动力粘性，在一个均匀的剪切流的不稳定平衡解与弯曲（流向移位反射和展向移位旋转）对称性的数值发现。小尺度特性由定义涡动粘性的混合长度尺度lS决定，大尺度运动由积分尺度上的平均剪切引起，而积分尺度上的平均剪切受展向盒维数Lz的限制。取R_{S}=L_{z}/L_{S}$作为数值延拓参数，它起着雷诺数的作用。结果表明，随着R_{S}$的增大，平衡解以鞍结分叉的形式出现，流场结构类似于具有同样弯曲对称性的平面Couette流。涡结构的低和上支的解决方案成为自发本地化的垂直方向。在低雷诺数时，下支解是一个边缘状态，随着雷诺数的增加，下支解呈现薄的临界层形式，这与一般剪切流的渐近理论在高雷诺数时的结果相同。另一方面，上分支的解决方案的特点是由一个高大的速度条纹多尺度多涡结构。在R_{S}$的高端，发现了一个初始的多尺度结构，LES湍流偶尔会到达垂直局域态，其涡结构类似于目前的垂直局域LES平衡。
Unstable equilibrium solutions in a homogeneous shear flow with sinuous (streamwise-shift-reflection and spanwise-shift-rotation) symmetry are numerically found in large-eddy simulations (LES) with no kinetic viscosity. The small-scale properties are determined by the mixing length scale $l_{S}$ used to define eddy viscosity, and the large-scale motion is induced by the mean shear at the integral scale, which is limited by the spanwise box dimension $L_{z}$ . The fraction $R_{S}=L_{z}/l_{S}$ , which plays the role of a Reynolds number, is used as a numerical continuation parameter. It is shown that equilibrium solutions appear by a saddle-node bifurcation as $R_{S}$ increases, and that the flow structures resemble those in plane Couette flow with the same sinuous symmetry. The vortical structures of both lower- and upper-branch solutions become spontaneously localised in the vertical direction. The lower-branch solution is an edge state at low $R_{S}$ , and takes the form of a thin critical layer as $R_{S}$ increases, as in the asymptotic theory of generic shear flow at high Reynolds numbers. On the other hand, the upper-branch solutions are characterised by a tall velocity streak with multiscale multiple vortical structures. At the higher end of $R_{S}$ , an incipient multiscale structure is found. The LES turbulence occasionally visits vertically localised states whose vortical structure resembles the present vertically localised LES equilibria.
库埃特流中的下分支平衡：任意剪切流的规范状态的出现
影响因子：
3.7
作者：
Blackburn H
通讯作者：
Blackburn H
影响因子：
3.7
作者：
Chandler, Gary J.;Kerswell, Rich R.
通讯作者：
Kerswell, Rich R.