Dispersed fibers change the classical energy budget of turbulence via nonlocal transfer

TL;DR

This study reveals how dispersed fibers alter turbulence energy transfer by introducing nonlocal interactions, leading to a new small-scale mixing mechanism and connecting porous media with suspension dynamics.

Contribution

It demonstrates the impact of dispersed fibers on turbulence energy budgets using advanced coupled simulations, revealing a universal back-reaction mechanism.

Findings

Turbulence loses kinetic energy at large scales due to fiber back-reaction.

A new energy-containing scale range emerges at small scales.

Anchored fibers induce similar effects as moving fibers with large inertia.

Abstract

The back-reaction of dispersed rigid fibers to turbulence is analyzed by means of a state-of-the-art fully-coupled immersed boundary method. The following universal scenario is identified: turbulence at large scales looses a consistent part of its kinetic energy (via a Darcy friction term), which partially re-appears at small scales where a new range of energy-containing scales does emerge. Large-scale mixing is thus depleted in favor of a new mixing mechanism arising at the smallest scales. Anchored fibers cause the same back-reaction to turbulence as moving fibers of large inertia. Our results thus provide a link between two apparently separated realms: the one of porous media and the one of suspension dynamics.