Abstract
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.
- Received 9 June 2017
- Revised 22 December 2017
DOI:https://doi.org/10.1103/PhysRevLett.120.124501
© 2018 American Physical Society
Physics Subject Headings (PhySH)
Viewpoint
Polymers Reduce Drag More than Expected
Published 19 March 2018
Adding polymer to a liquid was thought to reduce drag only up to a point, but new experiments have found exceptions to the usual limit.
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