论文标题
内部摩擦对湍流中线圈拉伸过渡的影响
Effect of internal friction on the coil-stretch transition in turbulent flows
论文作者
论文摘要
当魏森伯格数字（即流量的Lyapunov指数的乘积和聚合物的松弛时间）超过临界值时，湍流中的聚合物会经历线圈拉伸过渡。通过在均质和各向同性，不可压缩的，湍流的流动和分析计算中，通过对弹性哑铃模型的布朗动力学模拟进行了内部摩擦对过渡的影响。结果是通过改编Balkovsky等人的大偏差理论来解释的。 [物理。 Rev. Lett。，2000，84，4765]到具有内部粘度的弹性哑铃。在湍流中，聚合物扩展的概率分布的独特特征是其幂律行为的延伸率大于平衡长度，并且小于轮廓长度。结果表明，尽管内部摩擦并未修改线圈拉伸过渡的关键魏森贝格数字，但它使概率分布的斜率更陡峭，从而使过渡器更加清晰。因此，内部摩擦为在大魏森贝格数量的实验中观察到的聚合物扩展分布的陡峭分布提供了可能的解释。
A polymer in a turbulent flow undergoes the coil-stretch transition when the Weissenberg number, i.e. the product of the Lyapunov exponent of the flow and the relaxation time of the polymer, surpasses a critical value. The effect of internal friction on the transition is studied by means of Brownian dynamics simulations of the elastic dumbbell model in a homogeneous and isotropic, incompressible, turbulent flow and analytical calculations for a stochastic velocity gradient. The results are explained by adapting the large deviations theory of Balkovsky et al. [Phys. Rev. Lett., 2000, 84, 4765] to an elastic dumbbell with internal viscosity. In turbulent flows, a distinctive feature of the probability distribution of polymer extensions is its power-law behaviour for extensions greater than the equilibrium length and smaller than the contour length. It is shown that although internal friction does not modify the critical Weissenberg number for the coil-stretch transition, it makes the slope of the probability distribution steeper, thus rendering the transition sharper. Internal friction therefore provides a possible explanation for the steepness of the distribution of polymer extensions observed in experiments at large Weissenberg numbers.
