Large-eddy simulation of a particle-laden turbulent channel flow

Large-eddy simulations of a vertical turbulent channel flow with 420,000 solid particles are performed in order to get insight into fundamental aspects of a riser flow The question is addressed whether collisions between particles are important for the ow statistics. The turbulent channel ow corresponds to a particle volume fraction of 0.013 and a mass load ratio of 18, values that are relatively high compared to recent literature on large-eddy simulation of two-phase ows. In order to simulate this ow, we present a formulation of the equations for compressible ow in a porous medium including particle forces. These equations are solved with LES using a Taylor approximation of the dynamic subgrid-model. The results show that due to particle-uid interactions the boundary layer becomes thinner, leading to a higher skin-friction coefcient. Important effects of the particle collisions are also observed, on the mean uid prole, but even more o on particle properties. The collisions cause a less uniform particle concentration\ud and considerably atten the mean solids velocity prole

Magnetic excitation of a granular gas as a bulk thermostat

A thermostat utilizing a varying magnetic field has been developed to agitate soft ferromagnetic particles in microgravity platforms for an investigation of an energy-dissipative granular gas. Although the method has experimentally realized a reasonably homogeneous spatial distribution of particles, the physics behind the magnetically excited particles has not been understood. Therefore, a numerical calculation based on the discrete element method is developed in this paper to explain the realization of homogeneously distributed particles. The calculation method allows considering inelastic and magnetic interactions between particles and tracking the motions due to those interactions during the excitation of the granular gas. The calculation results, compared with the experimental result, show that magnetic interactions between particles, a time-domain variation of magnetic-excitation directions, and random collisions of particles between each magnetic excitation contribute to distribute particles homogeneously

Validation of the CFD-DPM solver DPMFoam in OpenFOAM (R) through analytical, numerical and experimental comparisons

Multiphase flows are relevant in several industrial processes mainly because they are present in the production of a large diversity of products. Hence, the availability of accurate numerical modeling tools, able to cope with this type of flows, is of major significance to provide detailed information about the system characteristics, in order to guide the design activity. This study presents a detailed assessment of a multiphase flow solver able to couple Eulerian and Lagrangian phases, the last modeled through the discrete particle method. The numerical code is already implemented in the open source computational fluid dynamics software package OpenFOAM ®. The solver (DPMFoam) is firstly used to simulate the collision between two particles, for which a good correlation was obtained with the theoretical impulse force value. Subsequently, the solver is employed in the simulation of a pseudo 2D gas-solid flow in a fluidized bed. In this case study, the results obtained for the bubble patterns, time-average flow patterns, bed expansion dynamics and particle phase energy analysis are in agreement with the experimental and numerical results available in the literature. In addition, the numerical pressure drop for the fluidized bed is computed and compared with the analytical Ergun’s pressure drop equation. The accuracy of the numerical results was found to be sensitive to the solid fraction estimation.This work is funded by FEDER funds through the COMPETE 2020 Programme and National Funds through FCT Portuguese Foundation for Science and Technology under the project EXPL/CTM-POL/1299/2013. In addition, the authors would like to acknowledge the Minho University cluster under the project SearchON2: Revitalization of HPC infractructure of Minho, (NORTE-070162-FEDER-000086), co-funded by the North Portugal Regional Operational Programme (ON.2-0 Novo Norte), under the National StrategicReferenceFramework(NSRF),throughtheEuropeanRegional Development Fund (ERDF).info:eu-repo/semantics/publishedVersio