Coupled CFD-DEM Research Articles

Coupling CFD-DEM and microkinetic modeling of surface chemistry for the simulation of catalytic fluidized systems.

In this work, we propose numerical methodologies to combine detailed microkinetic modeling and Eulerian-Lagrangian methods for the multiscale simulation of fluidized bed reactors. In particular, we couple the hydrodynamics description by computational fluid dynamics and the discrete element method (CFD-DEM) with the detailed surface chemistry by means of microkinetic modeling. The governing equations for the gas phase are solved through a segregated approach. The mass and energy balances for each catalytic particle, instead, are integrated adopting both the coupled and the operator-splitting approaches. To reduce the computational burden associated with the microkinetic description of the surface chemistry, in situ adaptive tabulation (ISAT) is employed together with operator-splitting. The catalytic partial oxidation of methane and steam reforming on Rh are presented as a showcase to assess the capability of the methods. An accurate description of the gas and site species is achieved along with up to 4 times speed-up of the simulation, thanks to the combined effect of operator-splitting and ISAT. The proposed approach represents an important step for the first-principles based multiscale analysis of fluidized reactive systems.

Coupled CFD-DEM with heat and mass transfer to investigate the melting of a granular packed bed

The eXtended Discrete Element Method (XDEM) platform which is a Coupled Eulerian-Lagrangian framework with heat and mass transfer, is extended for melting of granular packed beds. In this method, the fluid is simulated by computational fluid dynamics (CFD) and the soft-sphere discrete element approach (DEM) is used for the particle system. A four-way coupling accounts for solid-liquid interaction via drag and buoyancy forces and the collisions between the particles and the walls. The contact forces between the particles and wall-particle contacts have been calculated by the hertz-mindlin model. The particles heat up, melt and shrink due to heat and mass exchange, and the temperature distributions inside the particles are described. In order to validate the method, melting of a single ice particle and of a packed bed of ice in flowing water have been carried out. Very good agreement between the simulation and experiment has been achieved. The effects of the temperature and velocity of flowing water on melting rate are also discussed.

Coupling CFD-DEM with dynamic meshing: A new approach for fluid-structure interaction in particle-fluid flows

Many important engineering applications involve the interaction of free-moving objects with dispersed multi-phase flows, however due to the challenge and complexity of modelling these systems, modelling approaches remain very limited and very few studies have been reported. This work presents a new method capable of addressing these problems. It integrates a dynamic meshing approach, used to explicitly capture the flow induced by free-moving large object(s), with a conventional CFD-DEM method to capture the behaviour of small particles in particle-fluid flow. The force and torque acting on the large object due to the fluid flow are explicitly calculated by integrating pressure and viscous stress acting on the object's surface and the forces due to collisions with both the smaller particles and other structures are calculated using a soft-sphere DEM approach. The developed model has been fully implemented on the ANSYS/Fluent platform due to its efficient handling of dynamic meshing and complex and/or free-moving boundaries, thus it can be applied to a wide range of industrial applications. Validation tests have been carried out for two typical gas-solid fluidization cases, they show good qualitative and quantitative agreement with reported experimental literature data. The developed model was then successfully applied to gas fluidization with a large immersed tube which was either fixed or free-moving. The predicted interacting dynamics of the gas, particle and tube were highly complex and highlighted the value of fully resolving the flow around the large object. The results demonstrated that the capability of a conventional CFD-DEM approach could be enhanced to address free-body fluid-structure interaction problems encountered in particle-fluid systems.

Coupled CFD-DEM simulation of hydrodynamic bridging at constrictions

This paper presents a coupled CFD-DEM approach to simulate the flow of particulate suspensions in the intermediate concentration regime where solid volume concentration is 1% < ϕ < 50%. In particular, hydrodynamic multi-particle bridging during flow through a single constriction in a rectangular channel is studied. It is shown that for neutrally buoyant, monodispersed particulate suspensions, the probability of jamming increases with the particle concentration. There also exists a critical particle concentration (ϕ*) for spontaneous bridging, which depends on the ratio of pore size to particle size, the flow velocity, the particle-fluid density contrast, and the flow geometry leading to the constriction. The ϕ* has a strong dependence on the outlet-to-particle relative size (Ro). For 1.5 ≤ Ro ≤ 2.5, a direct transition from a flowing state to a jammed state was observed. For Ro ≥ 3, the flowing state typically transitioned to a dense state characterized by the accumulation of particles near the constriction before jamming. Increasing the inlet-to-particle relative size (Rip) lowers ϕ* by increasing the number of particles arriving at the constriction simultaneously. The effect of changing Rip is more pronounced at high Ro when the probability of bridging is lower. A high fluid velocity increases particle interactions near the constriction and accelerates the onset of bridging. However, no distinct effect of velocity on ϕ* was observed in this study. A higher particle-to-fluid density ratio (ρp/ρf) increases the probability of bridging and leads to a lower ϕ* in a given constriction geometry. The effect saturates at higher ρp/ρfwhen gravitational forces completely dominate over viscous drag forces. ϕ* is also found to decrease with increasing angle of constriction convergence (θ) for θ < 30°, but increases beyond that at θ=60∘.

Coupled CFD–DEM of particle-laden flows in a turning flow with a moving wall

The nature of the particle–solid interactions and particle–fluid interactions in rectangular duct bend geometry with/without a moving wall is studied, taking into account particle collision, colloidal, and hydrodynamic forces, and four way coupling between the fluid flow and particles. The focus is on systems where particles and fluid phase have similar length scales, fluid Reynolds number (Ref)∼1, and particle's Stokes number (St)∼1. Particles move toward the walls of the channel near the bend, and have long residence times in these regions. Buoyancy force has negligible effect on particle motion, where adhesion and drag forces lead to particle motion and agglomeration patterns. The effect of a free surface on agglomeration sites in the turning flow is elucidated.

A Coupled CFD-DEM Model for Simulating the Rheology of Particulate Suspensions

This paper describes the development of a numerical model used to study the rheology of particulate suspensions. A combination of computational fluid dynamics (CFD) and the discrete element method (DEM) was used to model the fluid and particulate phases, respectively. Initially, CFD models of different rheometer geometries were tested for both a Newtonian and a non-Newtonian fluid. Once the single-phase model had been validated, a coupled model combining CFD and DEM was created. This coupled model is currently capable of modelling spherical particles in a suspending liquid. DLVO forces were included to account for the surface charge on particles. Different numerical parameters were evaluated for their suitability for this problem. These parameters were used to test the models response to changes in solids volume concentration and different particle surface charge. When compared to experimental data, the model produced similar trends.

An efficient 4 way coupling CFD–DEM model for dense gas–solid particulate flows simulations

The goal of this paper is to illustrate how some recent numerical developments enable the simulation of dense two-phase flows. A coupled Computational Fluid Dynamic and Discrete Element Method (CFD–DEM) approach has been designed for the simulation of 3D fluidized beds. DEM is employed to model the granular particle phase while classical CFD is used to simulate the fluid flow by solving the Volume Averaged Navier-Stokes (VANS) equations. A special emphasize is put on the implementation of the velocity–pressure algorithm in the context of two-phase flows. By taking into consideration all particle–particle, fluid–particle and particle–wall interactions, a complete 4 way coupling model has been derived. Three dimensional computations of a single bubble formation as well as of the bubbly regime have been conducted. The simulations point out the existence of complex structures, such as the worm-like shape one, similar to those that have already been described in the literature.

Coupled CFD–DEM simulation of fluid–particle interaction in geomechanics

This paper presents a coupled Computational Fluid Dynamics and Discrete Element Method (CFD–DEM) approach to simulate the behaviour of fluid–particle interaction for applications relevant to mining and geotechnical engineering. DEM is employed to model the granular particle system, whilst the CFD is used to simulate the fluid flow by solving the locally averaged Navier–Stokes equation. The particle–fluid interaction is considered by exchanging such interaction forces as drag force and buoyancy force between the DEM and the CFD computations. The coupled CFD–DEM tool is first benchmarked by two classic geomechanics problems where analytical solutions are available, and is then employed to investigate the characteristics of sand heap formed in water through hopper flow. The influence of fluid–particle interaction on the behaviour of granular media is well captured in all the simulated problems. It is shown in particular that a sand pile formed in water is more homogeneous in terms of void ratio, contact force and fabric anisotropy. The central pressure dip of vertical stress profile at the base of sandpile is moderately reduced, as compared to the dry case. The effects of rolling resistance and polydispersity in conjunction with the presence of water on the formation of sandpile are also discussed.

Effect of Device Design on the Aerosolization of a Carrier-Based Dry Powder Inhaler—a Case Study on Aerolizer® Foradile®

The objective of this study is to investigate the effect of device design of the Aerolizer(®) on the aerosolization of a carrier-based dry powder inhaler formulation (Foradile(®)). The Aerolizer was modified by reducing the air inlet size and mouthpiece length to 1/3 of the original dimensions, or by increasing the grid voidage. Aerosolization of the powder formulation was assessed on a multi-stage liquid impinger at air flow rates of 30, 60, and 100 L/min. Coupled CFD-DEM simulations were performed to investigate the air flow pattern and particle impaction. There was no significant difference in the aerosolization behavior between the original and 1/3 mouthpiece length devices. Significant increases in FPF total and FPF emitted were demonstrated when the inlet size was reduced, and the results were explained by the increases in air velocity and turbulence from the CFD analysis. No significant differences were shown in FPF total and FPF emitted when the grid voidage was increased, but more drugs were found to deposit in induction port and to a lesser extent, the mouthpiece. This was supported by the CFD-DEM analysis which showed the particle-device collisions mainly occurred in the inhaler chamber, and the cross-grid design increased the particle-device collisions on both mouthpiece and induction port. The air inlet size and grid structure of the Aerolizer(®) were found to impact significantly on the aerosolization of the carrier-based powder.

2701 オープンソースCFDEMを用いたCFD-DEM連成解析について

2701 オープンソースCFDEMを用いたCFD-DEM連成解析について