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A study of a flexible fiber model and its behavior in DNS of turbulent channel flow

Journal article
Authors Jelena Andric
Sam Fredriksson
Stefan B. Lindström
Srdjan Sasic
Håkan Nilsson
Published in Acta Mechanica
Volume 224
Issue 10
Pages 2359-2374
ISSN 0001-5970
Publication year 2013
Published at Department of Earth Sciences
Pages 2359-2374
Language en
Links dx.doi.org/10.1007/s00707-013-0918-...
https://gup.ub.gu.se/file/114036
Keywords flexible fiber model, Direct Numerical Simulation (DNS), CFD
Subject categories Fluid mechanics

Abstract

The dynamics of individual flexible fibers in a turbulent flow field have been analyzed, varying their initial position, density and length. A particlelevel fiber model has been integrated into a general-purpose, open source Computational Fluid Dynamics (CFD) code. The fibers are modeled as chains of cylindrical segments connected by ball and socket joints. The equations of motion of the fibers contain the inertia of the segments, the contributions from hydrodynamic forces and torques, and the connectivity forces at the joints. Direct Numerical Simulation (DNS) of the incompressible Navier–Stokes equations is used to describe the fluid flow in a plane channel and a one-way coupling is considered between the fibers and the fluid phase. We investigate the translational motion of fibers by considering the mean square displacement of their trajectories. We find that the fiber motion is primarily governed by velocity correlations of the flow fluctuations. In addition, we show that there is a clear tendency of the thread-like fibers to evolve into complex geometrical configurations in a turbulent flow field, in fashion similar to random conformations of polymer strands subjected to thermal fluctuations in a suspension. Finally, we show that fiber inertia has a significant impact on reorientation time-scales of fibers suspended in a turbulent flow field.

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