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Polymer and surface roughness effects on the drag crisis for falling spheres

  • Physics of Fluids
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Abstract.

We make time resolved velocity measurements of steel spheres in free fall through liquid using a continuous ultrasound technique. We explore two different ways to induce large changes in drag on the spheres: 1) a small quantity of viscoelastic polymer added to water and 2) altering the surface of the sphere. Low concentration polymer solutions and/or a pattern of grooves in the sphere surface induce an early drag crisis, which may reduce drag by more than 50% compared to smooth spheres in pure water. On the other hand, random surface roughness and/or high concentration polymer solutions reduce drag progressively and suppress the drag crisis. We also present a qualititative argument which ties the drag reduction observed in low concentration polymer solutions to the Weissenberg number and normal stress difference.

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Correspondence to J.-F. Pinton.

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Lyotard, N., Shew, W., Bocquet, L. et al. Polymer and surface roughness effects on the drag crisis for falling spheres. Eur. Phys. J. B 60, 469–476 (2007). https://doi.org/10.1140/epjb/e2008-00018-0

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  • DOI: https://doi.org/10.1140/epjb/e2008-00018-0

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