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.

中文翻译：

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超过聚合物减阻的渐近极限

通过添加少量的高分子量聚合物，可以显着降低湍流的阻力。虽然减阻作用最初会随着聚合物浓度的增加而增加，但最终会饱和到所谓的最大减阻作用（MDR）渐近线。这种渐近线通常归因于动力学被简化为屈服的湍流运动的边缘但持久的状态。与这种公认的观点相反，我们表明，对于适当的参数选择，聚合物可以将阻力减小到建议的渐近极限之外，从而消除湍流并让层流流动。然而，在较高的聚合物浓度下，层流状态变得不稳定，从而导致流量波动，并带有MDR渐近线的特有阻力。