Large-eddy simulation of turbulent gas–particle flow in a vertical channel: effect of considering inter-particle collisions

Abstract

The interaction between a turbulent gas flow and particle motion was investigated by numerical simulations of gas–particle turbulent downward flow in a vertical channel. In particular the effect of inter-particle collision on the two-phase flow field was investigated. The gas flow field was obtained by large-eddy simulation (LES). Particles were treated by a Lagrangian method, with inter-particle collisions calculated by a deterministic method. The spatial resolution for LES of gas–solid two-phase turbulent flow was examined and relations between grid resolution and Stokes number are presented. Profiles of particle mean velocity, particle wall-normal fluctuation velocity and number density are flattened as a result of inter-particle collisions and these results are in good agreement with experimental measurements. Calculated turbulence attenuation by particles agrees well with experimental measurements for small Stokes numbers, but not for large Stokes number particle. The shape and scale of particle concentrations calculated considering inter-particle collision are in good agreement with experimental observations.

Lagrangian filtered density function for LES-based stochastic modelling of turbulent particle-laden flows

“…The first LES of particle-laden flow, in particular, was performed under the assumption of negligible contribution of the SGS fluctuations to the filtered fluid velocity seen by inertial particles [11]: The choice was justified considering that inertial particles act as low-pass filters that respond selectively to removal of SGS flow scales according to a characteristic frequency proportional to 1/τ p , where τ p is the particle relaxation time (a measure of particle inertia). The same assumption has been used in other studies [12][13][14][15] in which the filtering due to particle inertia and the moderate Reynolds number of the flow had a relatively weak effect on the (one-particle, two-particles) dispersion statistics examined. However, several studies [16][17][18] have demonstrated that neglecting the effect of SGS velocity fluctuations on particle motion leads to significant errors in the quantification of large-scale clustering and preferential concentration, two macroscopic phenomena that result from particle preferential distribution at the periphery of strong vortical regions into low-strain regions [19][20][21].…”

Consistent large-eddy simulation of a temporal mixing layer laden with evaporating drops. Part 1. Direct numerical simulation, formulation and a priori analysis

“…Consistent LES then means tracking a reduced number of drops; 'computational' drops are thus used to represent the physical drops. In this context, TP LES has additional modelling requirements compared to SP LES; whereas DNS requires modelling the interaction between individual drops and the unfiltered flow field, in LES neither the individual drops nor the unfiltered flow field are available and their interaction must be modelled from that between the filtered flow field and the computational drops.Recent LES of TP flows include those by Deutsch & Simonin (1991), Simonin, Deutsch & Boivin (1993, Uijttewaal & Oliemans (1996), Wang & Squires (1996), Boivin, Simonin & Squires (2000, and Yamamoto et al (2001). These LES all considered an incompressible gas phase laden with small solid particles, with the particles not affecting the evolution of the gas phase, i.e.…”

“…Wang & Squires (1996) found SGS effects, included by modifying the gas-phase velocity felt by the particles, to be negligible. The LES of Boivin et al (2000) and Yamamoto et al (2001) included two-way coupling, but still neglected SGS effects on the particles. The SGS modelling requirement in these studies was confined to the gas phase, facilitating the use of the large body of work on SGS flux models for incompressible SP flow.…”

Investigation of droplet dynamics in a convective cloud using a Lagrangian cloud model

“…Results from LES and direct numerical simulation (DNS) of particle-laden turbulent flows have shown that singleparticle statistics, such as the turbulent dispersion of particles, is not significantly affected by the subgrid-scale (SGS) motions of LES, except near the wall, as they are mainly controlled by large-scale eddies, but particle-pair statistics, such as particle collision and preferential concentration, are sensitive to small-scale eddies (Yeh and Lei 1991;Uijttewaal and Oliemans 1996;Wang and Squires 1996;Armenio et al 1999;Yamamoto et al 2001;Fede and Simonin 2006). Therefore, in the present LCM, the transport of a droplet is calculated by following the trajectory of a Lagrangian droplet using LES, while the collision/coalescence process and preferential concentration are parameterized.…”