Two- and Four-Way Coupled Euler–Lagrangian Large-Eddy Simulation of Turbulent Particle-Laden Channel Flow

Abstract

Large-eddy simulations (LES) of a vertical turbulent channel flow laden with a very large number of solid particles are performed. The motivation for this research is to get insight into fundamental aspects of co-current turbulent gas-particle flows, as encountered in riser reactors. The particle volume fraction equals about 1.3%, which is relatively high in the context of modern LES of two-phase flows. The channel flow simulations are based on large-eddy approximations of the compressible Navier-Stokes equations in a porous medium. The Euler-Lagrangian method is adopted, which means that for each individual particle an equation of motion is solved. The method incorporates four-way coupling, i.e., both the particle-fluid and particle-particle interactions are taken into account. The results are compared to single-phase channel flow in order to investigate the effect of the particles on turbulent statistics. The present results show that due to particle-fluid interactions the mean fluid profile is flattened and the boundary layer is thinner. Compared to single-phase turbulent flow, the streamwise turbulence intensity of the gas phase is increased, while the normal and spanwise turbulence intensities are reduced. This finding is generally consistent with existing experimental data. The four-way coupled simulations are also compared with two-way coupled simulations, in which the inelastic collisions between particles are neglected. The latter comparison clearly demonstrates that the collisions have a large influence on the main statistics of both phases. In addition, the four-way coupled simulations contain stronger coherent particle structures. It is thus essential to include the particle-particle interactions in numerical simulations of two-phase flow with volume fractions around one percent.

Turbulence modification and heat transfer enhancement by inertial particles in turbulent channel flow

“…This effect has been found before in DNS and LES (large-eddy simulation) of wall-bounded particle-laden flow at high mass loading. 7,26 In case 2Wn, the number of particles is smaller than in cases 2 W and 2Wcp. This results in a smaller reduction of the fluctuating wall-normal velocity r.m.s.…”

“…This results in a smaller reduction of the fluctuating wall-normal velocity r.m.s. Hence, the turbophoresis is between that of case 2 W and 1 W. It is known that four-way coupling plays a role if the particle volume fraction is large, see for example Vreman et al, 7 where the particle volume fraction is larger than 1%. Turbophoresis leads to increased particle volume fractions close to the walls, but this effect is significantly reduced by the two-way coupling, so that also close to the walls, the particle volume fraction stays well below 1%, motivating our use of two-way coupling as the dominant mechanism throughout the domain.…”

“…The present study applies two-way coupling only and ignores the direct inter-particle interactions. Results of Vreman et al 7 can be used to show that the effect of particle collisions is still small for particle volume fractions below 1%, which motivates our use of two-way coupling as the dominant mechanism for particle-fluid interaction.…”

Turbulence attenuation in particle-laden flow in smooth and rough channels

“…Others have shown that p-p collisions significantly flatten the mean particle velocity profile and the mean particle volume fraction velocity profile at low volume fractions (Li et al 2001;Yamamoto et al 2001;Vreman 2007;Nasr et al 2009). At larger volume fractions p-p collisions were shown to enhance the transfer from the kinetic energy in the streamwise particle velocity fluctuations to the kinetic energy in both the normal and spanwise particle velocity fluctuations (Vreman et al 2009). …”

Aerosol dynamics in porous media

“…For this purpose the point-particle approximation is very suitable, allowing to evaluate the trajectories of individual particles at low computational cost [44,58]. For resolving the gas flow we use a symmetry-preserving finite-volume discretization on a staggered grid [56].…”