Exceeding the Asymptotic Limit of Polymer Drag Reduction
Exceeding the Asymptotic Limit of Polymer Drag Reduction
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DOI：
10.1103/physrevlett.120.124501
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发表时间：
2018-03-19
影响因子：
8.6
通讯作者：
Hof, Bjoern
中科院分区：
文献类型：
--
作者：
Choueiri, George H.;Lopez, Jose M.;Hof, Bjoern
湍流的阻力可以通过添加少量的高分子量聚合物而显著降低。虽然减阻最初随着聚合物浓度增加，但它最终饱和到所谓的最大减阻（MDR）渐近线;这种渐近线通常归因于动力学被降低到轻微但持久的湍流运动状态。相反，这个公认的观点，我们表明，对于一个适当的选择参数，聚合物可以减少阻力超过建议的渐近极限，消除湍流和让位给层流。然而，在较高的聚合物浓度下，层流状态变得不稳定，导致具有MDR渐近线的特征阻力的波动流。我们的研究结果表明，渐近状态，因此动态断开普通湍流。
The drag of turbulent flows can be drastically decreased by adding small amounts of high molecular weight polymers. While drag reduction initially increases with polymer concentration, it eventually saturates to what is known as the maximum drag reduction (MDR) asymptote; this asymptote is generally attributed to the dynamics being reduced to a marginal yet persistent state of subdued turbulent motion. Contrary to this accepted view, we show that, for an appropriate choice of parameters, polymers can reduce the drag beyond the suggested asymptotic limit, eliminating turbulence and giving way to laminar flow. At higher polymer concentrations, however, the laminar state becomes unstable, resulting in a fluctuating flow with the characteristic drag of the MDR asymptote. Our findings indicate that the asymptotic state is hence dynamically disconnected from ordinary turbulence.