Large-Scale Direct Numerical Simulation for Investigating the Mesoscale Structure in Gas-Solid Flow
A coupled Lattice Boltzmann Method and Discrete Element Method (LBMâDEM) approach is usually a kind of particle-resolved direct numerical simulation (DNS) algorithms for modeling gas-solid two-phase flows, in which the size of fluid grid is generally one magnitude smaller than particle diameter and force acting on particles directly calculated by integrating both viscos force and pressure gradient force on the particleâs surface. It has been regarded as the most accurate numerical method for simulation of gas-solid flow. However, the main disadvantage is its huge computational cost resulting from small grid size and time step limited by Kolmogorov length and time scales. Only hundreds of particles scale is reported for DNS of gas-solid flow in the latest literature, which is very different from the number of particles in the real gas-solid flows. In order to solve the problem of computational speed and scale, an immersed boundary method in framework of LBM has been adopt to realized the fluid-solid coupling to avoid a stair-step representation of the solid particlesâ surfaces (Wang et al., 2010; Zhou et al., 2011) and the multi graphics processor units (GPUs) parallel computing of LBMâDEM approach has been implemented. Taking advantage of the inherent parallelism of LBM and the attractive Flops/Price ratio of GPU, we have implemented 576 GPUs parallel computing on a Mole-8.5 system and conducted the largest scale DNS of gas-solid suspensions so far, with 1,166,400 solid particles in an area of 11.5cm x 46cm for a two-dimensional system and 129,024 solid particles in a domain of 0.384cm x 1.512cm x 0.384cm for a three-dimensional system (Xiong et al., 2012). The scale of DNS data has been reached the size in traditional computational grid, which implies the really meaningful statistical results from large-scale DNS of gas-solid flows were obtained for the first time. The effects of mesoscale structure on the interaction force between gas and solid phases (Zhou et al., 2014) and the statistical properties of particles (Liu et al., 2017) were explored, which may provide the corresponding constitutive relation and detailed microscopic information for discrete particle simulation and two-fluid model.
Keywords: Lattice Boltzmann method; Discrete element method; Direct numerical simulation; Mesoscale structure; Gas-solid flow
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