Drag Reduction by a Linear Viscosity Profile

Abstract

Drag reduction by polymers in turbulent flows raises an apparent contradiction: the stretching of the polymers must increase the viscosity, so why is the drag reduced? A recent theory proposed that drag reduction in agreement with experiments is consistent with the effective viscosity growing linearly with the distance from the wall. With this self consistent solution the reduction in the Reynolds stress overwhelms the increase in viscous drag. In this Letter we show, using Direct Numerical Simulations, that a linear viscosity profile indeed reduces the drag in agreement with the theory and in close correspondence with direct simulations of the FENE-P model at the same flow conditions.

4 pages, 5 figures, JFM, submitted

References in corpus (2)

• Drag Reduction by Polymers in Wall Bounded Turbulence
• Drag Reduction by Polymers in Turbulent Channel Flows: Energy Redistribution Between Invariant Empirical Modes

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• Additive Equivalence in Turbulent Drag Reduction by Flexible and Rodlike Polymers
• Drag Reduction by Bubble Oscillations
• Saturation of Turbulent Drag Reduction in Dilute Polymer Solutions
• Phenomenology of Wall Bounded Newtonian Turbulence
• Rotational relaxation time as unifying time scale for polymer and fiber drag reduction
• Turbulent pipe flow with spherical particles: drag as a function of particle size and volume fraction