Local drag of a slender rod parallel to a plane wall in a viscous fluid

Lyndon Koens, Thomas D. Montenegro-Johnson

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The viscous drag on a slender rod by a wall is important to many biological and industrial systems. This drag critically depends on the separation between the rod and the wall and can be approximated asymptotically in specific regimes, namely far from, or very close to, the wall, but is typically determined numerically for general separations. In this article we determine an asymptotic representation of the local drag for a slender rod parallel to a wall which is valid for all separations. This is possible through matching the behavior of a rod close to the wall and a rod far from the wall. We show that the leading order drag in both these regimes has been known since 1981 and that they can be used to produce a composite representation of the drag which is valid for all separations. This is in contrast to a sphere above a wall, where no simple uniformly valid representation exists. We estimate the error on this composite representation as the separation increases, discuss how the results could be used as resistive-force theory, and demonstrate their use on a two-hinged swimmer above a wall.
Original languageEnglish
Article number064101
Number of pages16
JournalPhysical Review Fluids
Issue number6
Publication statusPublished - 24 Jun 2021

ASJC Scopus subject areas

  • Computational Mechanics
  • Modelling and Simulation
  • Fluid Flow and Transfer Processes


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