"Drag anisotropy of cylindrical solids in fluid-saturated granular beds" by Ankush Pal and Arshad Kudrolli
 

Physics

Drag anisotropy of cylindrical solids in fluid-saturated granular beds

Document Type

Article

Abstract

We study the direction-dependent drag acting on a cylindrical solid intruder with length L and diameter D as it moves in water-saturated granular beds at constant depth. Polysterene and hydrogel grains with diameter d are used to investigate materials which have high contact friction and those which are nearly frictionless, respectively. The drag on the intruder is measured while oriented perpendicular F1 and parallel F1 to its axis as a function of speed U from the quasistatic to the rate-dependent regime. We find that the drag anisotropy ζ=F1/F1 is not constant and increases significantly with driving rate and L/D in both mediums. In particular for L/D=40, ζ increases from 2.6 to 4.5, and from 7.0 to 8.2 in the high-and low-friction beds, respectively, as the nondimensional Froude number Fr=U/g(D+d) is varied between 10-4 and 2×10-2. On average, ζ is observed to increase logarithmically with L/D for L/D≫1. Exploiting the index-matched nature of hydrogel grains in water, we further show that the sediment flow around the cylinder in the two orientations is consistent with skin friction-dominated drag. The relative contributions of the cylindrical side and the circular flat-ends on ζ are estimated with thin disks to understand the observed variation of drag with aspect ratio and surface friction.

Publication Title

Physical Review Fluids

Publication Date

12-2021

Volume

6

Issue

12

ISSN

2469-990X

DOI

10.1103/PhysRevFluids.6.124302

Keywords

biomechanics, granular flows, granular materials

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