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Effect of subcritical fluid shear flow on granular bed strength

Dong Wang1, Sophie Bodek2, Nicholas T. Ouellette2, Mark D. Shattuck3, and Corey S. O'Hern1,4,5,6,*

  • 1Department of Mechanical Engineering, Yale University, New Haven, Connecticut 06520, USA
  • 2Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305, USA
  • 3Benjamin Levich Institute and Physics Department, The City College of New York, New York, New York 10031, USA
  • 4Department of Physics, Yale University, New Haven, Connecticut 06520, USA
  • 5Department of Applied Physics, Yale University, New Haven, Connecticut 06520, USA
  • 6Department of Materials Science, Yale University, New Haven, Connecticut 06520, USA

  • *Contact author: corey.ohern@yale.edu
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Phys. Rev. Fluids 11, 114304 – Published 12 November, 2026

DOI: https://doi.org/10.1103/2rpg-z6pt

Abstract

Interactions between fluids and granular materials are prevalent on the Earth's surface. In the case of fluid flow over a sediment bed, the fluid imparts a shear stress to the granular materials. When the applied shear stress is above a critical value, the grains become entrained in the fluid flow. Prior experimental studies have shown that granular beds subjected to a subcritical fluid flow can strengthen in the same direction as the subcritical flow. In contrast, granular beds can become weaker in the direction opposite to the subcritical fluid flow. To investigate the grain-scale mechanisms that control directional strengthening and weakening, we perform discrete element method simulations of granular beds subjected to model fluid flows in two and three dimensions with varied interparticle static friction coefficients and conditioning flow speeds. In these studies, the subcritical grain motion does not cause significant bed compaction. Instead, we find that the strength of a granular bed in a particular direction is highly correlated with the fraction of surface grains that can be dislodged by a fluid force applied in that direction. Further, the anisotropic bed strength only persists over a finite timescale that is set by the Shields number. We also show that interparticle static friction is not required for bed strength anisotropy, but varying the friction affects the magnitude of the anisotropy. This research enhances the grain-scale understanding of erosion of granular beds caused by fluid flows and underscores the importance of tracking the history of the fabric of the bed surface since it couples strongly to bed strength.

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Phys. Rev. Fluids 11, 114304– Published 12 November, 2026
  • Received 16 April 2026
  • Accepted 26 October 2026
Article part of CHORUS
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