Fluid-particle Systems Research Articles

Metaball-Imaging discrete element lattice Boltzmann method for fluid–particle system of complex morphologies with case studies

Fluid–particle systems are highly sensitive to particle morphologies. While many attempts have been made on shape descriptors and coupling schemes, how to simulate particle–particle and particle–fluid interactions with a balance between accuracy and efficiency is still a challenge, especially when complex-shaped particles are considered. This study presents a Metaball-Imaging (MI) based Discrete Element Lattice Boltzmann Method (DELBM) for fluid simulations with irregular shaped particles. The major innovation is the MI algorithm to capture the real grain shape for DELBM simulations, where the Metaball function is utilized as the mathematical representation due to its versatile and efficient expressiveness of complex shapes. The contact detection is tackled robustly by gradient calculation of the closest point with a Newton–Raphson based scheme. The coupling with LBM is accomplished by a classic sharp-interface scheme. As for refiling, a local refiling algorithm based on the bounce back rule is implemented. Validations on the Jeffery orbit of ellipsoidal particles and three settling experiments of irregular-shaped natural cobblestones indicate the proposed model to be effective and powerful in probing micromechanics of irregular-shaped granular media immersed in fluid systems. The potential of this model on studies of shape-induced physical processes is further investigated with numerical examples that consider the drag and lift forces experienced by realistic particles, as well as the “drafting, kissing and tumbling” process of pairs of non-spherical particles.

Assembly and manipulation of responsive and flexible colloidal structures by magnetic and capillary interactions.

The long-ranged interactions induced by magnetic fields and capillary forces in multiphasic fluid-particle systems facilitate the assembly of a rich variety of colloidal structures and materials. We review here the diverse structures assembled from isotropic and anisotropic particles by independently or jointly using magnetic and capillary interactions. The use of magnetic fields is one of the most efficient means of assembling and manipulating paramagnetic particles. By tuning the field strength and configuration or by changing the particle characteristics, the magnetic interactions, dynamics, and responsiveness of the assemblies can be precisely controlled. Concurrently, the capillary forces originating at the fluid-fluid interfaces can serve as means of reconfigurable binding in soft matter systems, such as Pickering emulsions, novel responsive capillary gels, and composites for 3D printing. We further discuss how magnetic forces can be used as an auxiliary parameter along with the capillary forces to assemble particles at fluid interfaces or in the bulk. Finally, we present examples how these interactions can be used jointly in magnetically responsive foams, gels, and pastes for 3D printing. The multiphasic particle gels for 3D printing open new opportunities for making of magnetically reconfigurable and "active" structures.

Numerical Investigations of Hydrodynamics in a Liquid-Solid Fluidized Bed

The liquid-solid fluidization bed is an effective method for removing hard ions from water. However, it is widely believed that the flow in the liquid-solid fluidization bed is homogeneous, which limits the transfer rates of heat, mass, momentum, and mixing. In this study, the results of the computational fluid dynamics (CFD) method showed significant heterogeneous particle–fluid patterns in the liquid-solid fluidization bed. On the other hand, simulations of the hydrodynamics behavior in the liquid-solid fluidized bed were first performed using different solid particle sizes, then particle classification, velocity distribution, and the vortical structures in the liquid-solid fluidized bed were assessed. In addition, a new model was proposed in this study to predict the flow behavior of the fluid-particle system used. The obtained results demonstrated the presence of the heterogeneous flow regime in the liquid-solid fluidized bed. The developed model for the onset of heterogeneous fluidization behavior revealed reasonable prediction results. Therefore, this model can be applied in future related studies on the hydrodynamics of the liquid-solid fluidized bed.

Microscale Modeling of Frozen Particle Fluid Systems with a Bonded-Particle Model Method

An inventive microscale simulation approach is applied to investigate the mechanics of frozen particle fluid systems (PFS). The simulation is based on the discrete element method (DEM) and bonded-particle model (BPM) approach. Discrete particles connected by solid bonds represent frozen agglomerates. Uniaxial compression experiments were performed to gather data for material modeling and further simulation model validation. Different typical mechanical behavior (brittle, ductile, dilatant) were reviewed regarding strain rates, saturation levels, and particle mechanical or surface properties. Among all these factors, strain rate significantly affects the mechanical behavior and properties of the agglomerates. A new solid bond model considering strain-dependent and time-dependent behavior is developed for describing the rheology of the frozen particle fluid systems. Without alternating Young's modulus and Poisson's ratio of the bond material, the developed solid model provides a suitable agreement with the experimental results regarding different strain rates.

A review of recent development for the CFD-DEM investigations of non-spherical particles

The coupling between fluid and granular materials is commonly encountered in nature and engineering practice. Moreover, the shape of granular materials in practical applications is normally non-spherical. Therefore, investigating the particle-fluid systems containing non-spherical particles for a deeper understanding of their underlying mechanisms and then for improving the performance of the related industrial processes should be an urgent necessity for practical needs. For investigating the intricate flow behaviors of particle-fluid systems, the numerical simulation method of coupling DEM (Discrete Element Method) with CFD (Computational Fluid Dynamics) has been widely recognized as a promising tool, and many efforts have been devoted to the CFD-DEM investigations of non-spherical particles in recent years. This paper aims to review development of the CFD-DEM investigations for non-spherical particles from theoretical models to applications in recent six years. It primarily represents three principal aspects: the theoretical foundations of DEM for modeling non-spherical particles, the coupling methodologies between CFD and DEM and the use of the non-spherical CFD-DEM coupling model in different applications involving particle-fluid flows. In the end, the conclusions and the outlooks for future investigations are given.

Chemical looping technology – a manifestation of a novel fluidization and fluid-particle system for CO2 capture and clean energy conversions

Chemical looping is broadly defined to represent processes that use chemical intermediates to decompose a reaction into two or more sub-reaction steps. Metal oxides are the typical chemical intermediates used for the chemical looping reactions although other metal derivatives are also used. Based on its intended applications, chemical looping encompasses calcium looping for CO 2 capture and redox looping for clean energy conversion applications. The redox looping has a longstanding history and has been demonstrated at multiple scales under various operating conditions since its conceptual inception about 120 years ago. Even with such extensive and prolonged efforts, redox looping is yet to be realized sustainably at a commercial level, while the calcium looping has been demonstrated for commercial applications. With growing concerns of climate change due to emissions of industrial greenhouse gases, efforts in developing redox looping processes as a promising fossil energy conversion technology with CO 2 emission control have been invigorated since the beginning of the 21st century. Metal oxide reaction engineering and particle science and technology have been the two enabling technical thrust areas, pivotal to advance the chemical looping concept to industrial practice. This article highlights some salient features of the chemical looping processes including a description of their historical development and illustration of the material screening and synthesis of oxygen carrier particles along with the representative process operational behavior. Recognizing that the configuration of chemical looping systems in their key operational scheme is established on the framework of circulating fluidized bed (CFB) systems, this article emphasizes the relevant characteristics of fluidization and fluid-particle systems with which the chemical looping technology is conducted. Both the fundamental and applied aspects of chemical looping processes and their associated CFB operation are discussed. • Chemical looping has garnered significant attention due to its inherent advantages. • The development of processes has been over 120 years. • Material screening and synthesis of oxygen carrier is the core. • System is related to many characteristics of fluidization and fluid-particle topic. • Fundamental and applied aspects of chemical looping processes are discussed.

Numerical Analysis Of a Falling Circular Particle Passing through a Fluid Channel having Diamond Shaped Obstacles

It has been analyzed that the particle motion inside a vertical channel while passing across diamond shaped obstacles produces severe effects on the fluid. Particle interaction with outer boundary, internal obstacles and with the fluid is inspected. An Eulerian based approach using a computational mesh is used in which solid particles are allowed to move freely in fluid domain. Fluid and particle interaction inside the whole domain is carried using Fictitious boundary method (FBM). A multigrid finite element method combined with the fictitious boundary method (FEM-FBM) is used for the simulation of in-compressible fluid flow along with rigid particle falling and colliding inside a fluid domain. A collision model to treat the Particle-obstacle and particle-wall interactions is used to avoid particle overlapping. The particulate flow is evaluated using an open source multigrid finite element solver FEATFLOW. Numerical investigations are executed in view of different particle positions and different alignment of diamond shaped obstacles. Effects on the movement of the particle and on the interaction of the fluid-particle system due to particle-wall, particle-Obstacle, particle-fluid interactivity has been analyzed.

Particle Scale Investigation of Influencing Factors on Heat Transfer in Nonspherical Particle–Fluid System

Abstract Heat transfer characteristics of random suspensions of 0.25 aspect ratio (AR) cylinders are investigated for Reynolds numbers (Re) between 10 and 300 and solid fraction (φ) ranging from 0.1 to 0.3 using particle resolved simulations. The effect of particle inclination with respect to flow and particle clustering on heat transfer is investigated. The Nusselt number decreases with an increase in inclination angle and the dependence becomes stronger as φ and Re increase. On the other hand, while prolate ellipsoid suspensions of AR 2.5 follow the same trend, the Nusselt number increases with inclination angle as AR increases to 5 and 10 and as φ increases. Local particle clustering nominally decreases the Nusselt number because of the dominance of thermal wakes. At low φ, this effect is felt only at low Re, but as φ increases, the effect spreads to higher Re. Similar but weaker trends are also found in suspensions of prolate ellipsoids of AR 2.5, 5, and 10. High AR, low Re prolate ellipsoids exhibit the greatest dependence of Nusselt number on local solid fraction. Implementation of two independent definitions of reference length, i.e., volume equivalent sphere diameter deq for ellipsoids and diameter dp of the cylindrical particle in the correlation of Tavassoli et al. (2015, “Direct Numerical Simulation of Fluid-Particle Heat Transfer in Fixed Random Arrays of Non-Spherical Particles,” Chem. Eng. Sci., 129, pp. 42–48) provides good estimates of the respective suspension mean Nusselt numbers.

Characterization of two-way coupled thermovibrationally driven particle attractee

Following the recent identification of a new category of thermovibrationally driven particle attractors in dilute fluid–particle systems [M. Lappa, “The patterning behaviour and accumulation of spherical particles in a vibrated non-isothermal liquid,” Phys. Fluids 26(9), 093301 (2014); M. Lappa, “On the formation and morphology of coherent particulate structures in non-isothermal enclosures subjected to rotating g-jitters,” Phys. Fluids 31(7), 073303 (2019); and M. Lappa and T. Burel, “Symmetry breaking phenomena in thermovibrationally driven particle accumulation structures,” Phys. Fluids 32(5), 053314 (2020)], some effort is provided here to develop an integrated framework able to encompass earlier discoveries and account for new effects in a single treatment. In particular, we examine the alterations (“corrugation”) that can be induced in the geometrically perfect particle structures pertaining to this class of phenomena as the percentage of dispersed solid mass is progressively increased. The related dynamics are explored within the framework of a two-way coupled model with respect to several parameters (solid mass load, density ratio, frequency, and amplitude of the imposed vibrations). Ensuing results are interpreted by separating instantaneous and time-averaged contributions and using some ideas borrowed from the companion theory of bifurcations. We show that the back influence of particles on the carrier flow can lead to a variety of possible paths of evolution. While in some cases the original attractee can be overshadowed by particle-induced turbulence, in other circumstances new aggregates with heretofore unseen morphology show up.

On the correction to Einstein’s formula for the effective viscosity

This paper is a follow-up to Gérard-Varet and Hillairet (2020) on the derivation of accurate effective models for viscous dilute suspensions. The goal is to identify an effective Stokes equation providing an o(\lambda^2) approximation of the exact fluid–particle system, with \lambda the solid volume fraction of the particles. This means that we look for an improvement of Einstein’s formula for the effective viscosity in the form \mu_{\mathrm{eff}}(x) = \mu + \frac{5}{2} \mu \rho(x) \lambda + \mu_2(x) \lambda^2 . Under a separation assumption on the particles, we proved in the article above that if an o(\lambda^2) Stokes effective approximation exists , the correction \mu_2 is necessarily given by a mean field limit, which can then be studied and computed under further assumptions on the particle configurations. Roughly, we go here from the conditional result of the article above to an unconditional result: we show that such an o(\lambda^2) Stokes approximation indeed exists, as soon as the mean field limit exists. This includes the case of periodic and random stationary particle configurations.

Superquadric DEM-SPH coupling method for interaction between non-spherical granular materials and fluids

The research on the coupling method of non-spherical granular materials and fluids aims to predict the particle–fluid interaction in this study. A coupling method based on superquadric elements is developed to describe the interaction between non-spherical solid particles and fluids. The discrete element method (DEM) and the smoothed particle hydrodynamics (SPH) are adopted to simulate granular materials and fluids. The repulsive force model is adopted to calculate the coupling force and then a contact detection method is established for the interaction between the superquadric element and the fluid particle. The contact detection method captures the shape of superquadric element and calculates the distance from the fluid particle to the surface of superquadric element. Simulation cases focusing on the coupling force model, energy transfer, and large-scale calculations have been implemented to verify the validity of the proposed coupling method. The coupling force model accurately represents the water entry process of a spherical solid particle, and reasonably reflects the difference of solid particles with different shapes. In the water entry process of multiple solid particles, the total energy of the water entry process of multiple solid particles tends to be stable. The collapse process of the partially submerged granular column is simulated and analyzed under different parameters. Therefore, this coupling method is suitable to simulate fluid–particle systems containing solid particles with multiple shapes.

Random walk discrete element lattice boltzmann model for scalar transport in fluid and particle flows with strict scalar mass conservation

Scalar transport in fluid-particle systems can be found in many natural processes and engineering applications. Modeling these systems can be challenging due to complex moving boundaries involved, such as fluid-particle, solute-particle interfaces. One often overlooked issue is: the scalar mass within the fluid domain is not strictly conserved even the no-flux boundary condition is applied in many grid-based methods. Here we introduce a hybrid model for simulating scalar transport in particulate flows with strict scalar mass conservation. It is achieved by adapting the Random Walk Method (RWM) to simulate the scalar transport and coupled with the Discrete Element Lattice Boltzmann Method (DE-LBM) for fluid-particle interactions. A moving boundary condition is proposed to prevent the scalar from penetrating solid boundaries and special treatments are presented in detail. The proposed model is validated by a series of benchmarks and experiments, then the mass conservation for both RWM and grid-based methods are checked. Finally, the model is applied to simulate scalar (solute) dispersion with particles in an oscillator which demonstrate its capability on simulating fluid-particle-solute systems. Furthermore, it is straightforward to extend the proposed model for non-spherical particles and reactive boundary conditions.

Examining the Behavior of a Solid Particle Interacting with Circular Obstacles in an Incompressible Flow

We have examined the effects on fluid and particle motion due to solid particles passing around circular obstacles in particulate flows. Particle interaction with internal obstacles, outer boundary and with the fluid is inspected. Eulerian approach using a fixed computational mesh is used across which the solid particles move freely in fluid. Treatment of fluid and particle interaction inside the whole domain is carried using Fictitious boundary method (FBM). A collision model is presented to handle particle-cylinder interactions. The particulate flow is computed using multigrid finite element solver FEATFLOW. Numerical experiments are performed considering different particle positions and different alignment of cylinders (obstacles). Effects on the motion of the particle and on the physical behavior of the fluid-particle system due to the particle-wall, particle-cylinder and particle-fluid interactions has been analyzed.

Numerical Simulation and Analysis of Large-scale Particle Fluid System Based on CFD-DPM Method

Numerical Simulation and Analysis of Large-scale Particle Fluid System Based on CFD-DPM Method

Particle plugging in porous media under stress dependence by Monte Carlo simulations

Accurate prediction of particle plugging behavior in porous media under stress conditions is crucial for characterizing particle flow in porous media. Specifically, due to particle plugging in porous media, rock deforms and permeability changes in the particle-fluid system. Therefore, it's significant to study particle plugging behavior in porous media under stress conditions. In this work, in view of the fractal character of pore structure and Hertz theory, probability models for stress dependent pore size and particle plugging strength (i.e., drag force exerting on the unit area of the particle) are developed using Monte carlo simulations. Compared with the existing models, our derived model considers more factors, such as pore structural parameters, particle size, lithology parameters of particles and rocks, and effective stress. The reliability of the derived model has been significantly improved due to the consideration of the more comprehensive influencing factors. Several case studies have been performed to validate the accraucy of the developed model. Eventually, the derived model has been applied to analyze a real case in Changqing reservoir in China and the analysis results show that our derived model can provide the theoretical basis to design the reasonable quantity of profile control agent (preformed particle gel) in oilfield.

A Comparison of Ansys Fluent and MFiX in Performing CFD-DEM Simulations of a Spouted Bed

The CFD-DEM methodology is a popular tool for the study of fluid–particle systems, and there are several programs that permit using it. In this study, we employed it to simulate a pseudo-2D spouted bed, comparing the performance of the programs Ansys Fluent and MFiX. The results are analysed and commented on in terms of both accuracy and computational efforts. Despite the similarity of the setup, MFiX seems to perform significantly better. The similarities and differences between the two programs are discussed in detail, offering useful insights to researchers regarding the selection of one over the other, depending on the application. The better suitability of the Di Felice drag model is confirmed for the device, while it is shown that the effect of the Magnus lift force may be more limited than was shown in a previous study.

Global Bounded Weak Entropy Solutions to the Euler--Vlasov Equations in Fluid-Particle System

In this paper, we consider a fluid-particle system which describes the evolution of a two-phase flow. The system consists of the compressible Euler equations for the fluid (fluid phase) coupled with the Vlasov equation for the particles (disperse phase) through the drag force. We obtain a global bounded weak entropy solution for such one-dimensional Euler--Vlasov equations with arbitrarily large initial data for the whole range of physical adiabatic exponents $\gamma>1$. To achieve this, we apply the vanishing viscosity method and compensated compactness theory. We construct globally defined approximate solutions by adding our novel viscosity terms to the Euler equations, which together with our key observation on relative velocity plays a fundamental role in the hardest part of our proof: the uniform $L^\infty$ estimate. After deriving an entropy dissipation estimate, we prove the convergence of approximate solutions by the compensated compactness argument.

Study of a Falling Rigid Particle Passing Around Obstacles in a Fluid Channel

We have examined the effects on fluid and particle motion due to solid particles passing around circular obstacles in particulate flows. Particle interaction with internal obstacles, outer boundary and with the fluid is inspected. Eulerian approach using a fixed computational mesh is used across which the solid particles move freely in fluid. Treatment of fluid and particle interaction inside the whole domain is carried using Fictitious boundary method. A modified collision model is presented to handle particle-cylinder interactions. The particulate flow is computed using multigrid finite element solver FEATFLOW. Numerical experiments are performed considering different particle positions and different alignment of cylinders (obstacles). Effects on the motion of the particle and on the physical behaviour of the fluid-particle system due to the particle-wall, particle-cylinder and particle-fluid interactions has been analysed.

Coupling of dilated polyhedral DEM and SPH for the simulation of rock dumping process in waters

The particle-fluid system can be simulated with the coupling model of the discrete element method (DEM) and the smoothed particle hydrodynamics (SPH), also named DEM-SPH coupling model. The dilated polyhedron, generated by the Minkowski sum of a sphere and a randomly shaped polyhedron, is adopted in the DEM. The contact detection between dilated polyhedron can be solved according to the potential function and geometric calculations between spheres, cylinders, and faces. The weakly compressible SPH is developed to establish the DEM-SPH coupling model. The interaction force between the solid particle and fluid particle is calculated by the repulsive force model, while the geometric shapes of the dilated polyhedron are directly used in the distance calculation. The dam break and the falling cube in the water are validated with previously published results. To simulate the rock dumping on the pipeline in the water, the contact detection algorithm between the sphere, the dilated polyhedron, and the pipe is developed. Numerical examples are illustrated to validate the proposed method. The rock dumping process is simulated to analyze the force on the pipe and the morphology of the dumping rocks. The results show that the proposed method is an effective approach for the rock dumping analysis.

An efficient framework for particle-fluid interaction using Discrete Element Lattice Boltzmann Method: Coupling scheme and periodic boundary condition

Discrete modeling of particle-fluid interaction was of great importance for its wide applications in chemical, petroleum and geotechnical engineering. Using Immersed Boundary Method (IBM) to couple Discrete Element Method (DEM) with Lattice Boltzmann Method (LBM) was adopted by many researchers to study particle-fluid systems. However, to accurately simulate the behavior of a large number of particles in the fluid, a huge computational power wasrequired to fully resolved the motion of each particle and an intensive search of particles’ contacts was needed to account for the collision between particles. In this paper, a periodic boundary was proposed for coupling DEM with LBM using IBM and an efficient particle contact detection algorithm was developed to further reduce the computation cost. The model was validated by several well-defined benchmark including: a single particle settling in a box, particle spinning in a channel and the well-known ‘Drafting, Kissing and Tumbling’ (DKT) effect of two settling disks. The model's applicability was exhibited in the simulation of sediments movement in a channel, which agreed well with previous experiments. These results showed the potential usage of present numerical model to investigate in particle-fluid interaction systems.