Coil-stretch transition in an ensemble of polymers in isotropic turbulence.
Coil-stretch transition in an ensemble of polymers in isotropic turbulence.
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DOI：
10.1103/physreve.81.066301
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发表时间：
2010-06
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影响因子：
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通讯作者：
Takeshi Watanabe;T. Gotoh
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文献类型：
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作者：
Takeshi Watanabe;T. Gotoh
本文研究了单向耦合条件下各向同性湍流中聚合物系综的统计特性。将受湍流被动对流作用的线性高分子链模型化为一排珠子，每个珠子由一个可伸缩的非线性弹性力连接，并服从布朗运动。我们发现当Weissenberg数Wi（η）为10时，它保持拉伸的时间比脉动湍流速度梯度的典型时间尺度长得多。表征聚合物系综的各种统计量，例如端到端矢量距离的平均值、方差、自相关时间和概率密度函数，表明螺旋拉伸转变发生在Wi（η）=3-4处。我们还发现，这种趋势对珠粒数量N（B）（N（B）=20或N（B）=2）不敏感，只要具有少量珠粒的模型中的参数是从具有大量珠粒的模型中正确生成的（即，使用Jin和柯林斯的公式）。最后，从局部流动拓扑学的角度考察了Wi（η）对端对端矢量与应变张量率主轴的排列以及对聚合物伸长的影响。
We study the statistical properties of ensembles of polymers in isotropic turbulence numerically in the one-way coupling regime. A linear polymer chain passively convected by turbulence is modeled by a line of beads, each of which is connected by a finitely extensible nonlinear elastic force and subject to Brownian motion. We find that when the Weissenberg number Wi(η)10, it remains stretched for a much longer time than the typical time scale of the fluctuating turbulent velocity gradient. Various statistical quantities characterizing the ensemble of polymers, such as the mean, variance, autocorrelation time, and probability density function of the end-to-end vector distance, indicate that the coil-stretch transition occurs at Wi(η)=3-4. We also find that this trend is insensitive to the number of beads N(b) ( N(b)=20 or N(b)=2), provided that the parameters in the model with a small number of beads are properly generated from the one with a large number of beads (i.e., using the formula of Jin and Collins). Finally, the Wi(η) effects on the alignment of the end-to-end vector versus the principal axis of the rate of strain tensor and on the polymer elongation are examined from the viewpoint of local flow topology.