Print Email Facebook Twitter The stress generated by non-Brownian fibers in turbulent channel flow simulations Title The stress generated by non-Brownian fibers in turbulent channel flow simulations Author Gillissen, J.J.J. Boersma, B.J. Mortensen, P.H. Andersson, H.I. Faculty Applied Sciences Department Multi-Scale Physics Date 2007-11-14 Abstract Turbulent fiber suspension channel flow is studied using direct numerical simulation. The effect of the fibers on the fluid mechanics is governed by a stress tensor, involving the distribution of fiber position and orientation. Properties of this function in channel flow are studied by computing the trajectories and orientations of individual particles, referred to as the particle method. It is shown that, due to computer restrictions, the instantaneous stress in channel flow cannot be simulated directly with the particle method. To approximate the stress we compute the second-order moment of the fiber distribution function. This method involves an unknown subgrid term, which is modeled as diffusion. The accuracy of the moment approximation is studied by comparing Reynolds averaged stress to results obtained from the particle method. It is observed that the errors are ? 1% for y+>20, and ? 20% for y+<20. The model is improved by applying a wall damping function to the diffusivity. The moment approximation is used to simulate drag-reduced channel flow. A simplified model for fiber stress is introduced as fiber viscosity times rate of strain, where fiber viscosity is defined as the ratio of Reynolds averaged dissipation due to fiber stress and Reynolds averaged dissipation due to Newtonian stress. Fluid velocity statistics predicted by the simple model compare very well to those obtained from the moment approximation. This means that the effect of fibers on turbulent channel flow is equivalent to an additional Reynolds averaged viscosity. Subject channel flowdiffusiondrag reductionfibresflow simulationstress analysisturbulence To reference this document use: http://resolver.tudelft.nl/uuid:3d6e7fe0-1849-4110-8e5e-5297702226be DOI https://doi.org/10.1063/1.2800041 Publisher American Institute of Physics ISSN 1070-6631 Source http://link.aip.org/link/PHFLE6/v19/i11/p115107/s1 Source Physics of Fluids, 19 (11), 2007 Part of collection Institutional Repository Document type journal article Rights (c) 2007 The Author(s); American Institute of Physics Files PDF Gillissen_2007.pdf 533.48 KB Close viewer /islandora/object/uuid:3d6e7fe0-1849-4110-8e5e-5297702226be/datastream/OBJ/view