Stokes number effects on particle slip velocity in wall-bounded turbulence and implications for dispersion models

Zhao, Lihao; Marchioli, Cristian; Andersson, Helge I.

doi:10.1063/1.3690071

Cited by 50 publications

(51 citation statements)

References 18 publications

(30 reference statements)

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“…In the core region of the channel, the fibre orientation was found to be isotropic. Mortensen et al 15,16 and Zhao et al 17,18 also observed that the particle slip velocity ) ( v u u   is largely dependent on the particle's distance from the wall (a measure of the fluid velocity gradient), and that lighter particles show a positive slip velocity whilst heavier particles exhibit a negative slip velocity in the viscous sub-layer but a positive value in the buffer layer.…”

Section: Introductionmentioning

confidence: 97%

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Simulation of inertial fibre orientation in turbulent flow

Njobuenwu

Fairweather

2016

Physics of Fluids

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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

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Section: Introductionmentioning

confidence: 97%

“…as it is at a distance from the wall at which the magnitudes of the mean slip velocity and the slip velocity fluctuations reach a maximum for spherical particles 17,18 . The next plane considered is also in the buffer Table 1 8, [14][15][16]18 .…”

Section: Instantaneous Fibre Concentrationmentioning

confidence: 99%

Simulation of inertial fibre orientation in turbulent flow

Njobuenwu

Fairweather

2016

Physics of Fluids

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“…In this work its effect was neglected for the sake of improving understanding of fluid-particle interaction within a manageable parameter range. This is common practice in the DNS and LES of particleladen, two-phase flow in a channel (Wang and Squires, 1996b;Wang and Squires, 1996a;Marchioli et al, 2008;Mortensen et al, 2008a, b;Marchioli et al, 2010;Zhao et al, 2012). For small sizes of ellipsoidal particles, the drag force also exhibits a greater influence on the particle dynamics than the lift force (Wang et al, 1997;Pan et al, 2001).…”

Section: Translational Motionmentioning

confidence: 99%

Dynamics of single, non-spherical ellipsoidal particles in a turbulent channel flow

Njobuenwu

Fairweather

2015

Chemical Engineering Science

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Using disk, spherical and needle-like particles with equal equivalent volume diameters, the orientational dynamics of non-spherical particles is studied in a turbulent channel flow. An Eulerian-Lagrangian approach based on large eddy simulation with a dynamic sub-grid scale model is used to predict a fully developed gassolid flow at a shear Reynolds number Re = 300. Particle shape and orientation are accounted for by the coupling between Newton's law of translational motion and Euler's law of rotational motion, both in a Lagrangian framework. The particle shapes are simulated using the super-quadrics form, with the dynamically relevant parameters being the particle aspect ratio, equivalent volume diameter and response time. The translational and orientational behaviour of single particles initially released at three different locations in the wall-normal direction are monitored, with analysis showing a clear distinction between the behaviour of the different particle shapes. The results show that turbulent dispersion forces non-spherical particles to have a broad orientation distribution. The orientational states observed include periodic, steady rotation, tumbling, precessing and nutating. Velocity gradient, aspect ratio and particle inertia all have an effect on the alignment of the particle principal axis to the inertial axes. Unlike spherical particles, the disk and needle-like particles display a transition from one orientational state to another, especially when their initial position is in the near-wall region, with the frequency of this transition highest for the disk-like particle. Overall, this study leads to an improved understanding of the significance of shape on particle behaviour which is of relevance to many practical flows.

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“…Some of the statistical results which will be presented in § 6 of this paper were obtained by conditional sampling rather than by conventional Reynolds-averaging. Conditional sampling has been used before in one-way coupled simulations, for instance by Squires & Eaton (1990), Mortensen et al (2007Mortensen et al ( , 2008 and Zhao, Marchioli & Andersson (2012). The fluid velocity of interest is that at the particle positions, since only that velocity is involved in the Stokes drag force in (2.5).…”

Section: Computer Simulationsmentioning

confidence: 99%

Interphasial energy transfer and particle dissipation in particle-laden wall turbulence

2013

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Transfer of mechanical energy between solid spherical particles and a Newtonian carrier fluid has been explored in two-way coupled direct numerical simulations of turbulent channel flow. The inertial particles have been treated as individual point particles in a Lagrangian framework and their feedback on the fluid phase has been incorporated in the Navier-Stokes equations. At sufficiently large particle response times the Reynolds shear stress and the turbulence intensities in the spanwise and wall-normal directions were attenuated whereas the velocity fluctuations were augmented in the streamwise direction. The physical mechanisms involved in the particle-fluid interactions were analysed in detail, and it was observed that the fluid transferred energy to the particles in the core region of the channel whereas the fluid received kinetic energy from the particles in the wall region. A local imbalance in the work performed by the particles on the fluid and the work exerted by the fluid on the particles was observed. This imbalance gave rise to a particleinduced energy dissipation which represents a loss of mechanical energy from the fluid-particle suspension. An independent examination of the work associated with the different directional components of the Stokes force revealed that the dominating energy transfer was associated with the streamwise component. Both the mean and fluctuating parts of the Stokes force promoted streamwise fluctuations in the near-wall region. The kinetic energy associated with the cross-sectional velocity components was damped due to work done by the particles, and the energy was dissipated rather than recovered as particle kinetic energy. Componentwise scatter plots of the instantaneous velocity versus the instantaneous slip-velocity provided further insight into the energy transfer mechanisms, and the observed modulations of the flow field could thereby be explained.

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Stokes number effects on particle slip velocity in wall-bounded turbulence and implications for dispersion models

Cited by 50 publications

References 18 publications

Simulation of inertial fibre orientation in turbulent flow

Simulation of inertial fibre orientation in turbulent flow

Dynamics of single, non-spherical ellipsoidal particles in a turbulent channel flow

Interphasial energy transfer and particle dissipation in particle-laden wall turbulence

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