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Many interesting particulate flow problems can only be studied using efficient numerical methods. We present a method based on a lattice Boltzmann fluid coupled to unresolved particles that interact with each other via the Discrete Element Method. Our method improves upon existing numerical schemes through the addition of a novel subcycling algorithm that guarantees momentum conservation during each DEM substep. The intended application is studying transport of solid particles in physiologic processes, although the method is generally applicable. We present in detail the development and (parallel) implementation of the model and show how intricacies of the coupling scheme must be considered to avoid unphysical behavior and instabilities. The scalability of the code is tested on two modern supercomputers. We demonstrate the method's applicability to biomedical applications by simulating the injection and distribution of particles in an idealized liver vasculature.   • 4-way coupled unresolved LBM-DEM method to simulate particulate flows. • Thorough discussion of the method's parallel implementation. • Novel subcycling scheme that guarantees momentum conservation at each DEM substep. • Scaling tests on two modern supercomputers up to 8192 CPU cores. • Application of the method to falling particle clouds and liver radioembolization. [ABSTRACT FROM AUTHOR]

An accurate representation of hydrodynamic force and torque experienced by every particle in a distribution can be obtained from particle resolved (PR) simulations. These unique quantities are influenced by the deterministic position of surrounding particles. However, systems simulated with this methodology are typically limited to O(10,000) particles due to the involved computational cost. This resource requirement is a major bottleneck in analyzing the effect of variations in particle distribution. This article attempts to address this bottleneck by availing relatively inexpensive deep learning models. The surrogate models that we employ in this article use a physics‐based hierarchical framework and symmetry‐preserving neural networks to achieve robustness with limited training data. This article first performs additional generalizability tests on PR data of distinct distributions that are not involved in the training process. The models are then deployed on several different particle distributions. Impact of clustering and structure on the observed statistics are investigated. [ABSTRACT FROM AUTHOR]

Measurement of the contact time for two spheres coated in a thin viscous film are considered. Measurements are performed using a Newton's cradle apparatus with a current passed through the apparatus such that the voltage can be used to infer the separation between the spheres. The spheres are coated with either a nonconductive viscous liquid (silicone oil) or a conductive liquid (glycerol and KCl). Measurement of the sphere‐film contact time and sphere‐sphere contact time for different film thicknesses and precollisional velocities are presented. Measurements of these contact times are compared to numerical simulations using the discrete element method (DEM). The results indicate that a solid‐solid contact is the physical mechanism which dictates rebound. A viscous force model where the interstitial liquid undergoes a glass transition was found to represent the dynamics of the system well, despite no glass transition being observed. [ABSTRACT FROM AUTHOR]

This paper presents a parallel algorithm for massive direct simulations of fluidized beds. It is based on an implicit–explicit (IMEX) technique for efficient and stable time integration of the incompressible Navier–Stokes equations in a domain that fits the boundaries of the particles at any time moment. The only modelling element in the algorithm is the model for particle–particle collisions, which is of the so‐called soft‐sphere type. The parallel performance of this technique is comparable to the performance of fully explicit methods. The numerical simulations of fluidized beds show very realistic effects that demonstrate the relevance of the simulation approach. [ABSTRACT FROM AUTHOR]

We carried out 3D simulations of monodisperse particle suspensions subjected to a constant shear rate with the view to investigate the effect of electrical double layers around the particles on apparent suspension viscosities. To this end, expressions for Debye length, zeta potential, and ionic strength (pH) of the liquid were incorporated into our in‐house lattice Boltzmann code that uses the immersed boundary method and includes subgrid lubrication models. We varied the solids concentration and particle radius, keeping the particle Reynolds number equal to 0.1. We report on results with respect to the effect of pH in the range 9 through 12 and of Debye length on apparent viscosity and spatial suspension structures, particularly at higher solids volume fractions, and on the effect of flow reversals. [ABSTRACT FROM AUTHOR]

Granular materials exhibit unique secondary flow behaviors upon shearing. We demonstrate, using particle dynamics simulations, that the secondary flow patterns are controlled by a pressure exerted on particle bed. A threshold pressure, at which vortex flow transitions to disturbed or chaotic flow, depends on particle shape, that influences interparticle contacts and rheological performance. Our results show that the flow patterns are essentially determined by a dimensionless term combining pressure and granular temperature for all the spherical and Platonic solid‐shaped particles explored. Particle mixing is promoted by the vortex flow or disturbed flow with strong diffusion. The highest mixing rate under a specified pressure is obtained for cubic particles, due to the significant microstructural ordering near the boundaries causing a high gradient of packing density. These findings shed light on how applied pressure and particle shape affect secondary flows which is critical to the understanding and control of granular mixing. [ABSTRACT FROM AUTHOR]

Clustering of flexible fibers in riser flows is investigated using a hybrid approach of Discrete Element Method and Computational Fluid Dynamics. Unlike spherical particles, the flexible fibers possess elongated shape, undergo significant deformation, and dissipate kinetic energies through rapid fiber deformation. The present studies show that these distinct features have significant impacts on the cluster characteristics of the fibers. A larger fiber aspect ratio leads to larger number and sizes of agglomerates, while it causes a reduction in heterogeneity of solids distribution due to the more dilute clusters with reduced packing densities. As the fibers become more flexible, the heterogeneity increases, and denser clusters are obtained. More significant effects of the fiber flexibility on the clustering are observed for the fibers with larger aspect ratios. The increased energy dissipation through the rapid fiber deformation enhances the clustering by augmenting the number and size of the agglomerates. [ABSTRACT FROM AUTHOR]

Oblique collisions of two spherical particles coated with a thin layer of viscous liquid are considered. Experimental measurements are performed using particle tracking velocimetry and the results are compared to viscous force and capillary force models via numerical simulation using the discrete‐element method. Comprehensive experimental data for collisions with an impact angle between 0° and 60° are presented to ensure future models can be rigorously validated. Collisions are characterized by the normal Stokes' number (a dimensionless ratio of normal inertial forces to normal viscous forces), and the normal coefficient of restitution (a dimensionless ratio of postcollisional normal velocity to precollisional normal velocity). Good agreement was found between the models and the experiments at high Stokes' number, where the models are dominated by the normal components. As the tangential forces become more significant (i.e., at low to medium Stokes' number, and high collision angle), agreement between the simulations and experiments is poorer. Furthermore, the models predict a decreasing rotational velocity with increasing Stokes' number past some critical Stokes' number. A coefficient of friction term was implemented and found to improve agreement for the rotational velocity postcollision. [ABSTRACT FROM AUTHOR]

Computational Fluid Dynamics - Discrete Element Method (CFD-DEM) is a powerful approach to simulate particulate flow in porous media at the pore-scale, and hence decipher the complex interplay between particle transport and retention. Two separate CFD-DEM approaches are commonly used in the literature: the unresolved (particle smaller than the grid cell size) and the resolved (particle bigger than the grid cell size) approach. In this paper, we propose a novel CFD-DEM coupling approach that combines both unresolved and resolved coupling. Our new modeling technique allows for the simulation of particulate flows in complex pore morphology characteristic of porous materials. It relies on an efficient searching strategy to find grid cells covered by the particles and on an appropriate calculation of the fluid-solid momentum exchange term. The robustness and efficiency of the computational model are demonstrated using cases for which reference solutions – analytical or experimental – exist. The new unresolved-resolved four-way coupling CFD-DEM is used to investigate pore-clogging and permeability reduction due to the sieving and bridging of particles. • Particulate transport in porous media at pore-scale leading to pore-clogging. • Unresolved-resolved Computational Fluid Dynamic-Discrete Element Method coupling. • Brinkman penalization technique for particulate flow. • Peer-to-peer searching strategy for covered cells of the Eulerian grid. • Isotropic diffusive smoothing of the void fraction in an Euler-Lagrange model. [ABSTRACT FROM AUTHOR]

This paper presents a computational approach for finding the optimal shapes of peristaltic pumps transporting rigid particles in Stokes flow. In particular, we consider shapes that minimize the rate of energy dissipation while pumping a prescribed volume of fluid, number of particles, and/or distance traversed by the particles over a set time period. Our approach relies on a recently developed fast and accurate boundary integral solver for simulating multiphase flows through periodic geometries of arbitrary shapes. In order to fully capitalize on the dimensionality reduction feature of the boundary integral methods, shape sensitivities must ideally involve evaluating the physical variables on the particle or pump boundaries only. We show that this can indeed be accomplished owing to the linearity of Stokes flow. The forward problem solves for the particle motion in a slip-driven pipe flow while the adjoint problems in our construction solve quasi-static Dirichlet boundary value problems backwards in time, retracing the particle evolution. The shape sensitivities simply depend on the solution of one forward and one adjoint (for each shape functional) problems. We validate these analytic shape derivative formulas by comparing against finite-difference based gradients and present several examples showcasing optimal pump shapes under various constraints. [ABSTRACT FROM AUTHOR]

Transport and particulate processes are ubiquitous in environmental, industrial and biological applications, often involving complex geometries and porous media. In this work we present a general population balance model for particle transport at the pore-scale, including aggregation, breakage and surface deposition. The various terms in the equations are analysed with a dimensional analysis, including a novel collision-induced breakage mechanism, and split into one- and two-particles processes. While the first are linear processes, they might both depend on local flow properties (e.g. shear). This means that the upscaling (via volume averaging and homogenisation) to a macroscopic (Darcy-scale) description requires closures assumptions. We discuss this problem and derive an effective macroscopic term for the shear-induced events, such as breakage caused by shear forces on the transported particles. We focus on breakage events as prototype for linear shear-induced events and derive upscaled breakage frequencies in periodic geometries, starting from nonlinear power-law dependence on the local fluid shear rate. Results are presented for a two-dimensional channel flow and a three dimensional regular arrangement of spheres, for arbitrarily fast (mixing-limited) events. Implications for linearised shear-induced collisions are also discussed. This work lays the foundations of a new general framework for multiscale modelling of particulate flows. [ABSTRACT FROM AUTHOR]

The effects of particle shape on settling behavior of sand particles under the influence of gravity in an initially quiescent water environment have been studied by a two-dimensional high-resolution numerical experiment. The numerical method is based on an immersed boundary method. The accuracy of the code is well demonstrated against experimental data of a fluttering rectangular plate. The particle is either elliptical or rectangular of size about 1 mm, and the particle aspect ratio is varied without changing the volume. The particle-to-fluid density ratio is chosen to be 2.65, and the resulting Galileo number is about 127. It is found that the terminal settling velocity tends to decrease with an increase in the aspect ratio and that the settling velocity of a rectangle is always lower than that of the corresponding ellipse in both the isolated and multiple particle systems. While the presence of surrounding particles makes the influence of the particle shape less clear, the circular particle still presents significant differences in the terminal settling velocity compared with the other particles. It, therefore, calls for caution in the spherical assumption of particle shape and encourages a deeper understanding of the particle shape effects. [ABSTRACT FROM AUTHOR]

The assumption of homogeneous isotropic turbulence when modeling drop breakage in industrially relevant geometries is questionable. We describe the development of an anisotropic breakage model, where the anisotropy is introduced via the inclusion of a perturbed turbulence spectrum. The selection of the perturbed spectrum is itself motivated by our previous large‐eddy simulations of high‐pressure homogenizers. The model redistributes energy from small to large scales, and assumes that the anisotropic part of the Reynolds stresses is confined to the energy‐containing range. The second‐order structure function arising from the perturbed spectrum is used in the standard framework of Coulaloglou and Tavlarides to calculate breakage frequency. While the base model exhibits non‐monotonic behavior (by predicting a maximum value for a certain drop size), the effect of anisotropy is shown to increase breakage frequency in length scales larger than this peak, thereby reducing non‐monotonicity. This effect is more pronounced for small turbulence Reynolds numbers. [ABSTRACT FROM AUTHOR]

In particulate systems, the ensemble average accounting for effects from all particles is expressed as the expected value related to the nearest particle probability. Using this expression, a stress is defined even for long-range particle interactions without the divergence difficulty because of the rapid far field decay of the probability. Similar to the potential part of the virial stress in molecular systems, this stress represents particle--particle interactions through the surrounding field. As examples, the stresses are calculated for systems of charged particles and disperse multiphase flows. [ABSTRACT FROM AUTHOR]

The diffusion of nonspherical particles has not been well understood due to the complexity of their contact mechanics and self‐organization of their orientations. We perform discrete element method simulations of monodisperse ellipsoids in a shear flow with Lees‐Edwards boundary conditions to quantify the relation between the diffusion coefficient and the flow parameters. The results indicate that the particle aspect ratio strongly affects the diffusion coefficient by influencing the particle orientation and alignment. We develop a scaling law for the diffusion coefficient perpendicular to the flow direction, Dyy, which combines the influences of the shear rate γ˙, the solids fraction f, the effective particle diameter deff and the particle aspect ratio Z. We show that Dyy=kdχf,Zγ˙deff2, where kd is a dimensionless pre‐factor, and a fit is obtained for the functional form of χ(f, Z). This scaling law will be useful in developing continuum transport models for applications. [ABSTRACT FROM AUTHOR]

QBMMlib is an open source package of quadrature-based moment methods and their algorithms. Such methods are commonly used to solve fully-coupled disperse flow and combustion problems, though formulating and closing the corresponding governing equations can be complex. QBMMlib aims to make analyzing these techniques simple and more accessible. Its routines use symbolic manipulation to formulate the moment transport equations for a population balance equation and a prescribed dynamical system. The resulting moment transport equations are closed by first trading the moments for a set of quadrature points and weights via an inversion algorithm, of which several are available. Quadratures then compute the moments required for closure. Embedded code snippets show how to use QBMMlib, with the algorithm initialization and solution spanning just 13 total lines of code. Examples are shown and analyzed for a linear harmonic oscillator and a bubble dynamics problem.

Particulate flows with charged particles under electric flow field exist in many practical applications, including metal particles in Gas Insulated Switchgear (GIS) or manipulation of powders in fluidized bed. The motions of these particles are affected by the electrical field, ambient flow and collisions. This work further develops the four-way coupled CFD-DEM framework under electric field, which not only computes the coupling of flow field, electric field with particle motion and particle charge, the particle-occupied solid fractions on CFD cell, particle-particle interactions and particle-wall interactions, but also considers the dielectrophoretic force, particle-particle Coulomb force, virtual mass force and Magnus force. Particle electrification on its contact with electrode is computed as well. Besides, the multi-sphere model is also introduced into the present framework in order to simulate particles of irregular shapes. The model is validated with theoretic solutions and experiments, and is applied to GIS and fluidized bed. Based on the framework, statistic information from the particulate flow in GIS, e.g., time-averaged solid fraction, time-averaged electric field or particles' velocity and charge distribution are analyzed. A dimensionless number is proposed to predict the particle motion in GIS with Alternating Current (AC), which is further conducive to reducing the parameter window in relevant simulations and studies. • The four-way coupled CFD-DEM modeling framework for charged particulate flows is extended with more concerned forces. • Fluid fraction is counted in the standard four-way coupling. • Multi-sphere model is introduced for modeling irregular-shaped particles. • Interesting phenomena of charged particles in GIS are revealed and discussed. • A dimensionless number is proposed to predict the particle motion in GIS. [ABSTRACT FROM AUTHOR]

Morphology and dynamics at the mesoscale play crucial roles in the overall macro- or system-scale flow of heterogeneous materials. In a multi-scale framework, closure models upscale unresolved sub-grid (mesoscale) physics and therefore encapsulate structure–property (S–P) linkages to predict performance at the macroscale. This work establishes a route to S–P linkage, proceeding all the way from imaged microstructures to flow computations in one unified level-set-based framework. Level sets are used to: (1) define embedded geometries via image segmentation; (2) simulate the interaction of sharp immersed boundaries with the flow field; and (3) calculate morphological metrics to quantify structure. Mesoscale dynamics is computed to calculate sub-grid properties, i.e., closure models for momentum and energy equations. The S–P linkage is demonstrated for two types of multi-material flows: interaction of shocks with a cloud of particles and reactive meso-mechanics of pressed energetic materials. We also present an approach to connect local morphological characteristics in a microstructure containing topologically complex features with the shock response of imaged samples of such materials. This paves the way for using geometric machine learning techniques to associate imaged morphologies with their properties. [ABSTRACT FROM AUTHOR]

A binary mixture is mixed in a rotating drum composed by 19 rings with different inner diameters. It is found that the larger particles are concentrated in the rings with smaller inner diameters. The collection of the larger particles in these rings is due to the particle dynamic angle of repose. The transition from the particle segregation core pattern at the end wall to the good radial mixing rings is through a transient turning comet segregation pattern. This transition is closely related to the distance from the ring with the smallest inner diameter to the ring with the largest inner diameter. Having a higher fraction of larger particles in a ring requires both the collection ring having a smaller inner diameter and a smoother inner diameter transition to the neighboring rings. [ABSTRACT FROM AUTHOR]

Aerosol deposition with gas phase-synthesized chain-like nanoaggregates can yield dense coatings from the impaction of particles on a substrate; however, dense coating formation is not well understood. Here, we study coating consolidation at the single nanoaggregate level. Flame spray pyrolysis-made tin oxide nanoaggregates are mobility (size) filtered, accelerated through a de Laval nozzle, and impacted on alumina substrates. TEM images obtained from low velocity collection and supersonic deposition are compared via quantitative image analysis, which reveals that upon supersonic impact nanoaggregates fragment into smaller aggregates. This suggests that fragmentation is a key step in producing coatings denser than the depositing nanoaggregates themselves. We supplement experiments with detailed particle trajectory calculations, which show that the impact energies per atom during nanoaggregate deposition are below 0.2 eV/molecule. These results suggest that fragmentation can only occur at locations where nanoaggregates bonded by van der Waals and capillary interactions. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation of the hydraulic conveying performance of coarse particles with the inlet pulsating fluid velocity in a vertical pipe. The influence of pulsating parameters, in terms of pulsating amplitudes and frequencies, on hydraulic conveying is mainly considered. The pulsations of particle and slip velocity are as periodic and regular as the inlet pulsating velocity. The variation of the normalized force in one pulsating time cycle is also analyzed. Then the laws of particle group distribution with transient time and vertical distance are obtained: the plug phenomenon is more obvious at the larger pulsating amplitude, further leading to pipe blockage, while a larger pulsating frequency is beneficial to the weakening of the plugs. Particle relaxation time is introduced to explain the changes in particle group distribution. Additionally, the temporal variations of flow fields are also used to illustrate the propagation of kinematic waves. [Display omitted] • An optimized CFD-DEM is used to investigate the hydraulic conveying in vertical pipe. • The effects of pulsating parameters on particle dynamics are analyzed. • The distribution laws of particle groups with pulsating parameters are obtained. • The propagation of kinematic waves with coarse particles is explored. [ABSTRACT FROM AUTHOR]

Discrete element method simulations of confined bidisperse granular shear flows elucidate the balance between diffusion and segregation that can lead to either mixed or segregated states, depending on confining pressure. Results indicate that the collisional diffusion is essentially independent of overburden pressure. Because the rate of segregation diminishes with overburden pressure, the tendency for particles to segregate weakens relative to the remixing of particles due to collisional diffusion as the overburden pressure increases. Using a continuum approach that includes a pressure‐dependent segregation velocity and a pressure‐independent diffusion coefficient, the interplay between diffusion and segregation is accurately predicted for both size and density bidisperse mixtures over a wide range of flow conditions when compared to simulation results. Additional simulations with initially segregated conditions demonstrate that applying a high enough overburden pressure can suppress segregation to the point that collisional diffusion mixes the segregated particles. © 2018 American Institute of Chemical Engineers AIChE J, 65: 875–881, 2019 [ABSTRACT FROM AUTHOR]

Abstract Simulations of dense suspensions containing arbitrary-shaped particles must deal with particle collision models. This paper deals with the wet collisional interactions between particles in a carrier fluid, in the context of immersed boundary treatment of fully resolved particles. When collisions of non-spherical particles occur, several parameters that govern collisional mechanics are challenging to obtain: these include collision point, normal and tangential forces, degree of overlapping between particles, the local relative velocity and the local curvatures at the collision point. These challenges are overcome in this paper by defining a field variable, i.e. a distance function that describes the particle on a regular Cartesian grid. A Simplified Spring Collision Method (SSCM) is proposed to model wet collision forces. The Stokes number at the collision point is computed from the particle's relative velocities and local curvatures and is used to calculate the restitution coefficient; damping is incorporated into the model by modifying the restitution coefficient when the rebound phase starts. The methods are validated against experiments and other benchmarks and shown to provide good results over a wide range of Stokes numbers. The capability of the method is also tested successfully for non-circular particle shapes. Graphical abstract Unlabelled Image Highlights • A collision model for resolved collision of arbitrary shape particles is proposed. • The collision parameters i.e. contact point, force, ... were calculated using the level-set field. • A spring system with no dashpot or lubrication model applies the collision force. • Collision forces are applied without creating stiff numerical schemes. [ABSTRACT FROM AUTHOR]

Abstract A discrete unified gas kinetic scheme (DUGKS) coupled with the immersed boundary (IB) method is developed to perform interface-resolved simulation of particle-laden flows. The present method (IB-DUGKS) preserves the respective advantages of the IB and DUGKS, i.e., the flexibility and efficiency for treating complex flows, and the robustness and low numerical-dissipation. In IB-DUGKS, the IB method is used to treat the fluid–solid interfaces and the DUGKS is applied to simulate the fluid flow, making use of the Lagrangian and Eulerian meshes, respectively. Those two meshes are fully independent, which contributes to the avoidance of grid regeneration when a solid particle moves. Specifically, in the present implementation of IB-DUGKS, the no-slip boundary condition at the particle surface is accurately enforced by introducing an efficient iterative forcing algorithm, and the IB force induced by the particle boundary is conveniently incorporated into the DUGKS with the Strang–Splitting scheme. The accuracy of the IB-DUGKS is first verified in the flows past a stationary cylinder and an oscillating cylinder in a quiescent fluid. After that, several well-established two- and three-dimensional particulate flow problems are simulated, including the sedimentation of a particle and the DKT dynamics of two particles in a channel, and a group of particles settling in an enclosure. In all test cases, the results are in good agreement with the data available in the literature, demonstrating that the proposed IB-DUGKS is a promising tool for simulating particulate flows. Highlights • IBM is successfully combined with DUGKS and the IB-DUGKS is proposed. • Force term is conveniently absorbed into DUGKS with Strang–Splitting scheme. • Application range of DUGKS is extended to moving boundary problems. • Three dimensional particle suspension flows are implemented. • Versatility and efficiency of IB-DUGKS is demonstrated in the simulations. [ABSTRACT FROM AUTHOR]

Highlights • A fully resolved simulation method of nonisothermal particulate flows by SP-LBM is proposed. • The temperature field is solved without any assumption. • The effect of the thermal expansion coefficient ratio on particles motion behaviours is investigated. Abstract A fully resolved simulation (FRS) method for particulate flows with heat transfer based on the smoothed profile-lattice Boltzmann method (SP-LBM) is developed. The governing equations of the flow field and the temperature field are solved by the LBM. The fluid-particle interaction is treated by the SPM. Both the no-slip boundary condition for the velocity field and the conjugate interface conditions for the temperature field are satisfied. Unlike many previous models, the present LB model removes the assumption that the particles have the uniform temperature. Motion of circular catalyst particles in an enclosure is simulated to validate our method. The effect of the thermal expansion coefficient ratio on particle motion behaviours is also investigated. [ABSTRACT FROM AUTHOR]

This paper presents a direct numerical simulation (DNS) technique, the Finite Element Fictitious Boundary Method (FEM-FBM) for the simulation of fluid-solid two-phase flows with heat transfer. The heat transfer equation is introduced to study thermal convection in fluid-solid two-phase flows. The Boussinesq approximation is considered for the coupling of momentum and temperature flow fields. Multi-grid finite element solver is used to compute flow equations of mass, momentum, and energy on a fixed Eulerian mesh which is independent of time and the solid particles are allowed to move freely in the whole computational domain. Fictitious boundary method (FBM) is used to treat the particles inside the fluid, FBM takes account of the thermal and momentum interaction between the fluid and the particles. The accuracy and stability of presented method are validated by comparing our test cases results with the results reported in the available literature. Numerical tests are performed to show that this method is potentially powerful and provides an efficient approach to simulate complex thermal convective particulate flows with a large number of particles. [ABSTRACT FROM AUTHOR]

Resistance force exerted on an obstacle in a gravity‐driven slow granular silo flow is studied by experiments and numerical simulations. In a two‐dimensional granular silo, an obstacle is placed just above the exit. Then, steady discharge flow is made and its flow rate can be controlled by the width of exit and the position of obstacle. During the discharge of particles, flow rate and resistance force exerting on the obstacle are measured. Using the obtained data, a dimensionless number characterizing the force balance in granular flow is defined by the relation between the discharge flow rate and resistance‐force decreasing rate. The dimensionless number is independent of flow rate. Rather, we find the weak shape dependence of the dimensionless number. This tendency is a unique feature for the resistance force in granular silo flow. It characterizes the effective flow width interacting with the obstacle in granular silo flow. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3849–3856, 2018 [ABSTRACT FROM AUTHOR]

Abstract The lattice Boltzmann method (LBM) has been widely considered as a distinctive and reliable approach for simulating the complex particulate flows. As an intrinsic kinetic scheme, it is quite convenient for LBM to apply the bounce-back (BB) type methods to handle the moving boundaries with complicated geometry, which is a tricky task for general interface-resolved methods. However, the two major schemes in LBM, i.e., the simple BB rule and the curved boundary condition (CBC) are presently encountered by the problems of low precision and loss of local computation, respectively. To overcome those two deficiencies in the boundary treatment simultaneously, a one-point second-order CBC is proposed in this paper. Information of only a single node is required in the present scheme, and the second-order accuracy is validated in the channel flow and cylindrical Couette flow. Applications to the particulate flows are further implemented to verify the present scheme. Numerical results are in good agreement with those in the literature. [ABSTRACT FROM AUTHOR]

Controlling heat and mass transfer in particulate suspensions has many applications in fuel combustion, food industry, pollution control and life science. We perform direct numerical simulations (DNS) to study the heat transfer within a suspension of neutrally buoyant, finite-size spherical particles in laminar and turbulent pipe flows, using the immersed boundary method (IBM) to account for the solid fluid interactions and a volume of fluid (VoF) method to resolve the temperature equation both inside and outside the particles. Particle volume fractions up to 40% are simulated for different pipe to particle diameter ratios. We show that a considerable heat transfer enhancement (up to 330%) can be achieved in the laminar regime by adding spherical particles. The heat transfer is observed to increase significantly as the pipe to particle diameter ratio decreases for the parameter range considered here. Larger particles are found to have a greater impact on the heat transfer enhancement than on the wall-drag increase. In the turbulent regime, however, only a transient increase in the heat transfer is observed and the process decelerates in time below the values in single-phase flows as high volume fractions of particles laminarize the core region of the pipe. A heat transfer enhancement, measured with respect to the single phase flow, is only achieved at volume fractions as low as 5% in a turbulent flow. [ABSTRACT FROM AUTHOR]

Vesicle suspensions appear in many biological and industrial applications. These suspensions are characterized by rich and complex dynamics of vesicles due to their interaction with the bulk fluid, and their large deformations and nonlinear elastic properties. Many existing state-of-the-art numerical schemes can resolve such complex vesicle flows. However, even when using provably optimal algorithms, these simulations can be computationally expensive, especially for suspensions with a large number of vesicles. These high computational costs can limit the use of simulations for parameter exploration, optimization, or uncertainty quantification. One way to reduce the cost is to use low-resolution discretizations in space and time. However, it is well-known that simply reducing the resolution results in vesicle collisions, numerical instabilities, and often in erroneous results. In this paper, we investigate the effect of a number of algorithmic empirical fixes (which are commonly used by many groups) in an attempt to make low-resolution simulations more stable and more predictive. Based on our empirical studies for a number of flow configurations, we propose a scheme that attempts to integrate these fixes in a systematic way. This low-resolution scheme is an extension of our previous work [51,53] . Our low-resolution correction algorithms (LRCA) include anti-aliasing and membrane reparametrization for avoiding spurious oscillations in vesicles' membranes, adaptive time stepping and a repulsion force for handling vesicle collisions and, correction of vesicles' area and arc-length for maintaining physical vesicle shapes. We perform a systematic error analysis by comparing the low-resolution simulations of dilute and dense suspensions with their high-fidelity, fully resolved, counterparts. We observe that the LRCA enables both efficient and statistically accurate low-resolution simulations of vesicle suspensions, while it can be 10× to 100× faster. [ABSTRACT FROM AUTHOR]

This paper presents a numerical simulation for dense particulate flows with coarse particles in inclined pipe to identify different flow regimes by means of computational fluid dynamics-discrete element method. The drag, gravitational, pressure gradient and virtual mass forces on particles, as well as the effect of particle–particle collisions are considered. Two flow regimes and their transitions are observed and described. The influence of Stokes number S t , Froude number F r , inclination angle β , etc., on critical flow regimes is analyzed to identify the dependence of flow regimes on these parameters. A new diagram for recognizing regime transition is given. The temporal variations of flow fields are also analyzed to illustrate propagating of kinematic waves. The wave velocity increases with F r , β , and particle concentration increasing. Two dimensionless numbers, collision stress and fluid–particle interaction stress, are defined to explain the regime transition mechanism. The maximum pressure drop occurs at approximately β = 60°. [Display omitted] • An optimized CFD-DEM is used to investigate dense particulate flows in inclined pipe. • The flow regimes and their transitions of dense particulate flows in inclined pipe are analyzed. • A new phase diagram for recognizing different flow regimes is given. • Temporal variations of particle quantities are analyzed to illustrate propagating of kinematic waves. [ABSTRACT FROM AUTHOR]

In this paper we introduce a one-fluid numerical method for the simulation of dense particle–fluid flows. The method uses a front tracking algorithm coupled to a viscous penalty method to enforce the rigidity constraint. A modified version of the collision model of Mohaghegh and Udaykumar (2019) is used to model both collisions and lubrication forces. This approach allows us to greatly reduce the amount of ad hoc numerical parameters required to perform the simulations. For validation purpose, we successfully reproduce several experimental and numerical benchmarks including the settling case of a sphere in an enclosed box performed by ten Cate et al. (2002), the bouncing motion against a planar surface performed by Gondret et al. (2002), the study of the fluid–solid fluidized bed performed by Aguilar-Corona (2008), and the particle-resolved simulations of the same case performed by Ozel et al. (2017). The method is shown to realistically reproduce the motion of a settling and a bouncing sphere in a quiescent fluid. The statistical study of the fluidized bed showed excellent agreement with the experimental data and the fluidization law: the solid volume fraction, the solid velocity variance and the anisotropy coefficient are accurately reproduced by our simulations. • Development of a Front-Tracking/DEM method for simulating particles resolved flows. • Proposal of a new model for both collisions and lubrication forces. • Validation with experimental and numerical benchmarks. • Statistical study of a fluidized bed. [ABSTRACT FROM AUTHOR]

Gas-solid fluidization involving small amounts of liquid is simulated using a CFD-DEM model. The model tracks the amount of liquid on each particle and wall element and incorporates finite rates of liquid transfer between particles and pendular liquid bridges which form between two particles as well as between a particle and a wall element. Viscous and capillary forces due to these bridges are modeled. Fluidization-defluidization curves show that minimum fluidization velocity and defluidized bed height increase with Bond number (Bo), the ratio of surface tension to gravitational forces, due to cohesion and inhomogeneous flow structures. Under fluidized conditions, hydrodynamics and liquid bridging behavior change dramatically with increasing Bo, and to a lesser extent with capillary number, the ratio of viscous to surface tension forces. Bed fluidity is kept relatively constant across wetting conditions when one maintains a constant ratio of superficial velocity to minimum fluidization velocity under wet conditions. © 2017 American Institute of Chemical Engineers AIChE J, 63: 5290-5302, 2017 [ABSTRACT FROM AUTHOR]

The effect of particle aspect ratio on the rheology of the flow of granular materials is studied experimentally in a quasi-two-dimensional rotating cylinder, using two varieties of prolate spheroidal grains with different aspect ratios. Image analysis of high speed videos is used to obtain the flow profiles near the centre of the cylinder. The dynamic angle of repose and apparent viscosity in the medium show significant increase with increasing aspect ratio. The mean velocity, root mean square velocity and shear rate profiles are qualitatively similar for nonspherical and spherical particles, however, their magnitudes increase with increasing aspect ratio. A simple scaling is shown to predict the maximum thickness of the flowing layer for all the particles. The predictions of a model for the flow match with the measured mean velocity profiles and layer thickness. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4307-4315, 2017 [ABSTRACT FROM AUTHOR]

Extrusion is a widely used process for forming suspensions and pastes into designed shapes, and is central to the manufacture of many products. In this article, the extrusion through a square-entry die of non-Brownian spheres suspended in Newtonian fluid is investigated using discrete element simulations, capturing individual particle-particle contacts and hydrodynamic interactions. The simulations reveal inhomogeneous velocity and stress distributions, originating in the inherent microstructure formed by the constituent particles. Such features are shown to be relevant to generic paste extrusion behavior, such as extrudate swell. The pressure drop across the extruder is correlated with the extrudate flow rate, with the empirical fitting parameters being linked directly to particle properties such as surface friction, and processing conditions such as extruder wall roughness. Our model and results bring recent advances in suspension rheology into an industrial setting, laying foundations for future model development, predictive paste formulation and extrusion design. © 2016 American Institute of Chemical Engineers AIChE J, 63: 3069-3082, 2017 [ABSTRACT FROM AUTHOR]

Using the approach of interacting and interpenetrating continua, a one-dimensional model is developed for the gravity-driven flow of particles and gas through a vertical standpipe. The gas and particle phases exchange momentum through the drag force, and mass is exchanged between the phases as the particles decompose to gaseous products. On simultaneously integrating the differential equations expressing conservation of mass and momentum for each of the two phases, the theory yields the particle and gas flow rates, the pressure profile, and the particle size and void fraction distributions. Performance diagrams are constructed, and preferred operating conditions are identified that provide steady flow, generate no backpressure, or avoid a transition to moving bed flow or reversed gas flow. The admissible range of operating conditions is found to increase with the particle decomposition rate, and the results may guide the selection of operating conditions in practice. Applications are made to biomass pyrolysis in a catalytic reactor. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2318-2334, 2017 [ABSTRACT FROM AUTHOR]

An accurate, efficient and robust numerical scheme is presented for the simulation of the interaction between flexibly-supported rigid bodies and incompressible fluid flow with topology changes and solid–solid contact. The solution of the incompressible Navier–Stokes equations is approximated by employing a stabilised formulation on Cartesian grids discretised with hierarchical b-splines. The solid is modelled as a rigid body and represented by linear segments along its boundary. Kinematic conditions along the fluid–rigid body interface are enforced weakly using Nitsche’s method, while ghost penalty operators are employed to avoid excessive ill-conditioning of the system matrix arising from small cut cells. A staggered scheme is used for resolving the coupled fluid–rigid body interaction. The contact between moving or moving and fixed solid bodies is modelled with Lagrange multipliers. The excellent performance and wide range of applicability of the proposed scheme are demonstrated in a number of benchmark tests as well as industrially relevant model problems. The examples cover the galloping phenomena, particulate flow, hydraulic check valves and a model turbine. [ABSTRACT FROM AUTHOR]

A helicopter flying through an atmosphere containing particulates may accumulate high electrostatic charges which can challenge its operational safety. In this paper we elaborate and validate a triboelectric charging model to predict the electrification experienced by a helicopter while hovering in dusty air. We employed Large Eddy simulations to describe the turbulent structures inherent in the flow around the rotorcraft. The dust particles were tracked individually in a Lagrangian framework. A model accounting for the triboelectric charge transfer when a particle hits the helicopter was introduced. The results demonstrate the accuracy of the proposed approach and allow a detailed analysis of the location of the charge accumulation. [ABSTRACT FROM AUTHOR]

The current study presents experiments for the initial stages of fluidization induced by a localized fluid injection. The process was studied by recording high-speed videos in a 2-D-region far from the boundaries using Planar Laser Induced Fluorescence and Refractive Index Matching. The experimental setup allowed for several parameters to be systematically studied including particle sizes, initial bed heights, and injection port diameters. The results show that the critical flow rate required for fluidization is primarily dependent on the initial height of the granular bed. However, this dependence is not a linear relation but progressively plateaus for larger heights. Conversely, the diameter of the chimney relates only slightly to the injection port diameter and significantly more to the diameter of the particles. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1529-1542, 2017 [ABSTRACT FROM AUTHOR]

The flow behavior of mixtures of micron-sized cubic particles suspended in a concentrated colloidal dispersion is investigated across a broad range of cubic particle concentrations. In the semi-dilute regime, the qualitative shape of the dynamic moduli and flow curves reflect those of the underlying colloidal dispersion medium. These curves are superimposed with the underlying colloidal dispersion using shift factors that are found to be larger than those obtained in a recent study of suspensions of non-colloidal spherical particles in the same colloidal dispersion medium. At higher concentrations of cubic particles, deviations from this shifting procedure are apparent. Scaling calculations suggest depletion interactions are responsible for the increase in the low shear viscosity and confinement of the underlying colloidal dispersion can be expected to enhance the shear thickening behavior at high shear stresses. The results of this study provide guidance for formulating suspensions through control of particle shape and mixture concentration. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1091-1101, 2017 [ABSTRACT FROM AUTHOR]

A population balance model appropriate for the shear flow of thixotropic colloidal suspensions with yield stress is derived and tested against experimental data on a model system available in the literature. Modifications are made to account for dynamic arrest at the onset of the yield stress, in addition to enforcing a minimum particle size below which breakage is not feasible. The resulting constitutive model also incorporates a structural based relaxation time, unlike existing phenomenological models that use the inverse of the material shear rate as the relaxation time. The model provides a reasonable representation of experimental data for a model thixotropic suspension in the literature, capturing the important thixotropic timescales. When compared to prevalent structure kinetics models, the coarse-grained population balance equation is shown to be distinct, emphasizing the novelty of utilizing population balances as a basis for thixotropic suspension modeling. © 2016 American Institute of Chemical Engineers AIChE J, 63: 517-531, 2017 [ABSTRACT FROM AUTHOR]