Statistics of rigid fibers in strongly sheared turbulence

TL;DR

This study experimentally investigates the orientation and dynamics of millimetric fibers in strongly sheared turbulent flow, revealing consistent preferential alignment and intermittent angular velocities that suggest point-particle-like behavior.

Contribution

It demonstrates that finite-sized fibers in turbulence exhibit predictable orientation and dynamics that can be explained by simplified models like Jefferey's equation.

Findings

Fibers show a preferred orientation of approximately -68 degrees relative to flow.

Jefferey's equation effectively explains fiber alignment despite finite size.

Fiber angular velocity exhibits strong intermittency, indicating flow signatures are retained.

Abstract

Practically all flows are turbulent in nature and contain some kind of irregularly-shaped particles, e.g. dirt, pollen, or life forms such as bacteria or insects. The effect of the particles on such flows and vice-versa are highly non-trivial and are not completely understood, particularly when the particles are finite-sized. Here we report an experimental study of millimetric fibers in a strongly sheared turbulent flow. We find that the fibers show a preferred orientation of $-0.38\pi \pm 0.05\pi$ ($-68 \pm 9^\circ$) with respect to the mean flow direction in high-Reynolds number Taylor-Couette turbulence, for all studied Reynolds numbers, fiber concentrations, and locations. Despite the finite-size of the anisotropic particles, we can explain the preferential alignment by using Jefferey's equation, which provides evidence of the benefit of a simplified point-particle approach. Furthermore, the fiber angular velocity is strongly intermittent, again indicative of point-particle-like behavior in turbulence. Thus large anisotropic particles still can retain signatures of the local flow despite classical spatial and temporal filtering effects.