Josephson-Anderson关系作为聚合物湍流减阻的诊断。

IF 2.4 3区 物理与天体物理 Q1 Mathematics
Samvit Kumar, Simon Toedtli, Tamer A Zaki, Gregory L Eyink
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引用次数: 0

摘要

详细的Josephson-Anderson关系将体积积分涡通量与压降做功瞬间等同起来,是超导体和超流体中减阻的关键。我们采用该关系的经典版本来研究聚合物减阻通道流动的动力学,特别是在已知表现出强时空间断性的高程度减阻(HDR)制度下。我们表明,高阻力不是由近壁相干涡结构瞬间产生的,正如以前的工作所假设的那样。这些主要沿展向的近壁涡结构可以产生朝向壁面的净“上升梯度”涡量通量,从而减少瞬时阻力。壁面涡度和壁面摩擦的增加是在平流数次明显滞后后发生的,随着Weissenberg数的增加而增加。这种增加的滞后似乎是由于聚合物阻尼了上梯度非线性涡量传输,这种传输是由对数层中的大规模涡流引起的。由于小尺度涡流,聚合物的下梯度输运阻尼相对较大,导致净涡量通量较低,因此阻力较小。因此,Josephson-Anderson关系为从涡量动力学角度诊断聚合物减阻机理提供了一个精确的工具,它还解释了之前在管道流动中心线释放实验中对瞬态减阻的令人困惑的观察结果。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Josephson-Anderson relation as diagnostic of turbulent drag reduction by polymers.

The detailed Josephson-Anderson relation, which equates instantaneously the volume-integrated vorticity flux and the work by pressure drop, has been the key to drag reduction in superconductors and superfluids. We employ a classical version of this relation to investigate the dynamics of polymer drag-reduced channel flows, particularly in the high-extent drag reduction (HDR) regime which is known to exhibit strong space-time intermittency. We show that high drag is not created instantaneously by near-wall coherent vortex structures as assumed in prior works. These predominantly spanwise near-wall vortex structures can produce a net "up-gradient" flux of vorticity toward the wall, which instead reduces instantaneous drag. Increase of wall vorticity and skin friction due to this up-gradient flux occurs after an apparent lag of several advection times, increasing with the Weissenberg number. This increasing lag appears to be due to polymer damping of up-gradient nonlinear vorticity transport that arises from large-scale eddies in the logarithmic layer. The relatively greater polymer damping of down-gradient transport due to small-scale eddies results in lower net vorticity flux and hence lower drag. The Josephson-Anderson relation thus provides an exact tool to diagnose the mechanism of polymer drag reduction in terms of vorticity dynamics and it explains also prior puzzling observations on transient drag reduction, as for centerline-release experiments in pipe flow.

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来源期刊
Physical review. E
Physical review. E 物理-物理:流体与等离子体
CiteScore
4.60
自引率
16.70%
发文量
0
审稿时长
3.3 months
期刊介绍: Physical Review E (PRE), broad and interdisciplinary in scope, focuses on collective phenomena of many-body systems, with statistical physics and nonlinear dynamics as the central themes of the journal. Physical Review E publishes recent developments in biological and soft matter physics including granular materials, colloids, complex fluids, liquid crystals, and polymers. The journal covers fluid dynamics and plasma physics and includes sections on computational and interdisciplinary physics, for example, complex networks.
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