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Mixing layer instability and vorticity amplification in a creeping viscoelastic flow

Atul Varshney1,2 and Victor Steinberg1,3

  • 1Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100, Israel
  • 2Institute of Science and Technology Austria, Am Campus 1, 3400 Klosterneuburg, Austria
  • 3The Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel

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Phys. Rev. Fluids 3, 103303 – Published 16 October, 2018

DOI: https://doi.org/10.1103/PhysRevFluids.3.103303

Abstract

We report quantitative evidence of mixing-layer elastic instability in a viscoelastic fluid flow between two widely spaced obstacles hindering a channel flow at Re≪1 and Wi≫1. Two mixing layers with nonuniform shear velocity profiles are formed in the region between the obstacles. The mixing-layer instability arises in the vicinity of an inflection point on the shear velocity profile with a steep variation in the elastic stress. The instability results in an intermittent appearance of small vortices in the mixing layers and an amplification of spatiotemporal averaged vorticity in the elastic turbulence regime. The latter is characterized through scaling of friction factor with Wi and both pressure and velocity spectra. Furthermore, the observations reported provide improved understanding of the stability of the mixing layer in a viscoelastic fluid at large elasticity, i.e., Wi≫1 and Re≪1 and oppose the current view of suppression of vorticity solely by polymer additives.

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Phys. Rev. Fluids 3, 103303– Published 16 October, 2018
  • Received 1 February 2018
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