Simulation of inertial fibre orientation in turbulent flow

Abstract

The spatial and orientational behaviour of fibres within a suspension influences the rheological and mechanical properties of that suspension. An Eulerian-Lagrangian framework to simulate the behaviour of fibres in turbulent flows is presented. The framework is intended for use in simulations of nonspherical particles with high Reynolds numbers, beyond the Stokesian regime, and is a computationally efficient alternative to existing Stokesian models for fibre suspensions in turbulent flow. It is based on modifying available empirical drag correlations for the translation of non-spherical particles to be orientation dependent, accounting for the departure in shape from a sphere. The orientational dynamics of a particle is based on the framework of quaternions, while its rotational dynamics is obtained from translational dynamics, in terms of preferential concentration, is strongly dependent on their inertia and less so on their aspect ratio. However, the contrary is the case for the fibre alignment distribution as this is strongly dependent on the fibre aspect ratio and velocity gradient, and only moderately dependent on particle inertia. The fibre alignment with the flow direction is found to be mostly anisotropic where the velocity gradient is large (i.e. viscous sub-layer and buffer regions), but is virtually non-existent and isotropic where the turbulence is near-isotropic (i.e. channel centre). The present investigation highlights that the level of fibre alignment with the flow direction reduces as a fibre's inertia decreases, and as the shape of the fibre approaches that of a sphere. Short fibres, and especially near-spherical 001 . 1  particles, are found to exhibit isotropic orientation with respect to all directions, whilst sufficiently long fibres align themselves parallel to the flow direction, and orthogonal to the other two co-ordinate directions, and the vorticity and flow velocity gradient directions.2

Dynamics of disk-like particles in turbulent vertical channel flow

“…By comparing corresponding lines between λ=0.33 and λ=0.1 at modest inertia, the preferential alignment of spheroid's long axis in the direction of fluid vorticity vector becomes slightly stronger for disks with greater departure from sphericity. This is consist with the results of L. and Njobuenwu and Fairweather (2016) that the alignment effect of spheroids becomes slightly stronger for particles with greater departure from sphericity, although the focus of their work is on the alignment of rod-like particles parallel to the local fluid vorticity in the channel center. In addition, increased particle inertia weakens the alignment effect for all particle shapes, making the orientation of disk-like particles more isotropic in the channel center.…”

“…F. Zhao et al (2013; studied fibers in wall turbulence using four-way coupling, and reported that the fluctuations of particle velocity are stronger than that of fluid velocity in the streamwise direction and significantly lower than of the fluid in the other directions in the near-wall region. It is also confirmed that large inertia prolate spheroids align parallel to local fluid vorticity in the central region (L. Njobuenwu and Fairweather, 2016), and the Lagrangian fluid stretching direction in the nearly isotropic turbulence should be responsible for the distinct alignment (Pumir and Wilkinson, 2011;Ni et al, 2014;Chen et al, 2016;.…”

Large eddy simulation of inertial fiber deposition mechanisms in a vertical downward turbulent channel flow

“…Hence, the degree of fibre clustering shown in this figure is not as pronounced as that reported in other studies 4,[19][20][21]34 , where strong clustering was observed for spheres and fibres around the buffer region and in turbulent flows without gravity. Additionally, the fibre distributions shown in Fig.…”

Simulation of deterministic energy-balance particle agglomeration in turbulent liquid-solid flows

“…This LES solver been validated thoroughly for many different flows, e.g. 35,36 BOFFIN solves the space-filtered mass and momentum conservation equations for an incompressible fluid, with the contributions of the dispersed phase being regarded as point sources of momentum:…”