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

N. Lyotard, W. L. Shew, L. Bocquet and J.-F. Pinton ()

The European Physical Journal B: Condensed Matter and Complex Systems, 2007, vol. 60, issue 4, 469-476

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. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2007

Keywords: 47.85.lb Drag reduction; 47.32.Ff Separated flows; 47.63.mc High Reynolds number motions (search for similar items in EconPapers)
Date: 2007
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Citations: View citations in EconPapers (1)

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DOI: 10.1140/epjb/e2008-00018-0

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