On the mechanism of elasto-inertial turbulence
On the mechanism of elasto-inertial turbulence
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DOI：
10.1063/1.4820142
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发表时间：
2013-11-01
影响因子：
4.6
通讯作者：
Soria, Julio
中科院分区：
文献类型：
--
作者：
Dubief, Yves;Terrapon, Vincent E.;Soria, Julio
弹性-惯性湍流（EIT）是在含有聚合物添加剂的惯性流中发现的一种新的湍流状态。从聚合物动力学和流动结构耦合的角度研究了由这些添加剂产生和控制的湍流动力学。直接数值模拟的通道流的雷诺数范围从1000到6000（基于体积和通道高度）被用来研究弹性不稳定性的形成和动力学及其对流动的影响。EIT的流动拓扑结构被发现显着不同于牛顿壁湍流。由速度梯度的正（旋转流拓扑）和负（拉伸/压缩流拓扑）第二不变Q（a）等值面识别的结构是圆柱形的并且在展向方向上对齐。聚合物在沿流向方向延伸的片状区域中显著拉伸，具有小的向上倾斜。Q（a）圆柱形结构出现在高分子拉伸片层中，能量从聚合物应力功的波动转移到湍流动能。在亚临界雷诺数，EIT观察到在适度的韦森伯格数（Wi，聚合物弛豫时间比粘性时间尺度）。对于超临界雷诺数，流动在大Wi下接近EIT。EIT的聚合物减阻（最大减阻）的渐近状态的性质提供了新的见解，并解释了早期湍流的现象，或在较低的雷诺数比在一些聚合物流中观察到的牛顿流的湍流发病。(C)2013 AIP Publishing LLC.
Elasto-inertial turbulence (EIT) is a new state of turbulence found in inertial flows with polymer additives. The dynamics of turbulence generated and controlled by such additives is investigated from the perspective of the coupling between polymer dynamics and flow structures. Direct numerical simulations of channel flow with Reynolds numbers ranging from 1000 to 6000 (based on the bulk and the channel height) are used to study the formation and dynamics of elastic instabilities and their effects on the flow. The flow topology of EIT is found to differ significantly from Newtonian wall-turbulence. Structures identified by positive (rotational flow topology) and negative (extensional/compressional flow topology) second invariant Q(a) isosurfaces of the velocity gradient are cylindrical and aligned in the spanwise direction. Polymers are significantly stretched in sheet-like regions that extend in the streamwise direction with a small upward tilt. The Q(a) cylindrical structures emerge from the sheets of high polymer extension, in a mechanism of energy transfer from the fluctuations of the polymer stress work to the turbulent kinetic energy. At subcritical Reynolds numbers, EIT is observed at modest Weissenberg number (Wi, ratio polymer relaxation time to viscous time scale). For supercritical Reynolds numbers, flows approach EIT at large Wi. EIT provides new insights on the nature of the asymptotic state of polymer drag reduction (maximum drag reduction), and explains the phenomenon of early turbulence, or onset of turbulence at lower-Reynolds numbers than for Newtonian flows observed in some polymeric flows. (C) 2013 AIP Publishing LLC.