Publications
81 publications
Calibration of particle interactions for discrete element modeling of powder flow
An experiment using an ASTM B213 standard Hall Flowmeter Funnel was conducted on Ti 6–4 powder particles and simulated via discrete element method in LIGGGHTS. Particle interactions were modeled with a modified Johnson–Kendall–Roberts theory incorporating adhesion based on surface free energy. The simulations used actual particle size distribution data and adjustable parameters like cohesion energy density, restitution coefficient, and dynamic friction were fine-tuned to resemble the experimental particle pile shape. Simulated geometrical properties of the powder pile were measured and compared to experimental outcomes. Local particle size variations within the pile were analyzed, revealing a segregation with larger particles at the top, similar to the Brazil nut effect.
An experiment using an ASTM B213 standard Hall Flowmeter Funnel was conducted on Ti 6–4 powder particles and simulated via discrete element method in LIGGGHTS. Particle interactions were modeled with a modified Johnson–Kendall–Roberts theory incorporating adhesion based on surface free energy. The simulations used actual particle size distribution data and adjustable parameters like cohesion energy density, restitution coefficient, and dynamic friction were fine-tuned to resemble the experimental particle pile shape. Simulated geometrical properties of the powder pile were measured and compared to experimental outcomes. Local particle size variations within the pile were analyzed, revealing a segregation with larger particles at the top, similar to the Brazil nut effect.
A viscoelastic bonded particle model to predict rheology and mechanical properties of hydrogel spheres
The study introduces a numerical simulation tool based on the Discrete Element Method tailored for predicting the behavior of hydrogel spheres, extensively used in various sectors due to their adaptable mechanical properties. Initially, the model's accuracy is assessed through an oscillatory compression test on a single hydrogel, achieving a close match with experimental rheological properties; the relative errors for the normal modified storage and loss moduli (E’ and E”) are about 3% and 11%, respectively. This approach, utilizing bonded particles and a viscoelastic constitutive relation, is validated further with a particle-particle compression test, showing promising alignment with experimental contact forces. This model's adaptability makes it suitable for a broad range of applications.
The study introduces a numerical simulation tool based on the Discrete Element Method tailored for predicting the behavior of hydrogel spheres, extensively used in various sectors due to their adaptable mechanical properties. Initially, the model's accuracy is assessed through an oscillatory compression test on a single hydrogel, achieving a close match with experimental rheological properties; the relative errors for the normal modified storage and loss moduli (E’ and E”) are about 3% and 11%, respectively. This approach, utilizing bonded particles and a viscoelastic constitutive relation, is validated further with a particle-particle compression test, showing promising alignment with experimental contact forces. This model's adaptability makes it suitable for a broad range of applications.
Comparing open-source DEM frameworks for simulations of common bulk processes
This study conducts a comparative analysis of nine widely-used, open-source Discrete Element Method (DEM) software frameworks for simulating granular materials. Each framework utilizes explicit time integration, involving contact detection, interaction calculations, and motion equation integration. Significant differences among them include contact models, particle shapes, data analysis methods, data structures, software architecture, parallelization techniques, and user interfaces. The benchmarks, using common bulk processes like silo emptying, drum mixing, and particle impact, employed standard features like spherical particles and the Hertz-Mindlin dry contact model. Scripts for these benchmarks are also provided, facilitating reproducibility and further testing.
This study conducts a comparative analysis of nine widely-used, open-source Discrete Element Method (DEM) software frameworks for simulating granular materials. Each framework utilizes explicit time integration, involving contact detection, interaction calculations, and motion equation integration. Significant differences among them include contact models, particle shapes, data analysis methods, data structures, software architecture, parallelization techniques, and user interfaces. The benchmarks, using common bulk processes like silo emptying, drum mixing, and particle impact, employed standard features like spherical particles and the Hertz-Mindlin dry contact model. Scripts for these benchmarks are also provided, facilitating reproducibility and further testing.
Predictions of the P1 approximation for radiative heat transfer in heterogeneous granular media
The P1 approximation, a simplified model for thermal radiation, is integrated into a combined CFD-DEM framework to enhance computational efficiency while handling dependent scattering and coarse-graining effects. Analysis using analytical solutions shows good agreement for steady-state and transient behaviors in size-disperse systems, though heat flux predictions exhibit unphysical oscillations due to temperature discrepancies at sharp changes in solid fraction. To address this, two solutions—smoothing radiative properties and introducing pseudo-scattering—are proposed. The framework supports extensive coarse-graining, tested up to a million times the particle size. Comparisons with experimental data from a pebbled bed in vacuum and nitrogen environments show that the model closely replicates observed trends, maintaining a relative temperature error under 10%.
The P1 approximation, a simplified model for thermal radiation, is integrated into a combined CFD-DEM framework to enhance computational efficiency while handling dependent scattering and coarse-graining effects. Analysis using analytical solutions shows good agreement for steady-state and transient behaviors in size-disperse systems, though heat flux predictions exhibit unphysical oscillations due to temperature discrepancies at sharp changes in solid fraction. To address this, two solutions—smoothing radiative properties and introducing pseudo-scattering—are proposed. The framework supports extensive coarse-graining, tested up to a million times the particle size. Comparisons with experimental data from a pebbled bed in vacuum and nitrogen environments show that the model closely replicates observed trends, maintaining a relative temperature error under 10%.
A comprehensive comparison of Two-Fluid Model, Discrete Element Method and experiments for the simulation of single- and multiple-spout fluidized beds
In this study, we use a two-fluid model (TFM) and a computational fluid dynamics-discrete element method (CFD-DEM) approach to analyze the time-averaged hydrodynamics of single- and multiple-spout fluidized beds. The simulations were validated using experimental data from van Buijtenen et al. (2011), incorporating four different interphase drag correlations. The TFM approach includes detailed kinetic theory modeling of granular flows with enhanced particle–wall interactions and an innovative modification of the -rheology to incorporate rolling friction effects. In contrast, the CFD-DEM method integrates rolling friction through an additional torque component. Both methods showed strong agreement in predicting key parameters such as volume fraction, particle velocities, fluxes, and granular temperature, demonstrating the robustness and accuracy of the models in simulating complex fluidized bed dynamics.
In this study, we use a two-fluid model (TFM) and a computational fluid dynamics-discrete element method (CFD-DEM) approach to analyze the time-averaged hydrodynamics of single- and multiple-spout fluidized beds. The simulations were validated using experimental data from van Buijtenen et al. (2011), incorporating four different interphase drag correlations. The TFM approach includes detailed kinetic theory modeling of granular flows with enhanced particle–wall interactions and an innovative modification of the -rheology to incorporate rolling friction effects. In contrast, the CFD-DEM method integrates rolling friction through an additional torque component. Both methods showed strong agreement in predicting key parameters such as volume fraction, particle velocities, fluxes, and granular temperature, demonstrating the robustness and accuracy of the models in simulating complex fluidized bed dynamics.
Single Particle Growth, Fragmentation and Morphology Modelling: A DEM Approach
The paper discusses the synthesis and characterization of polyacrolein using radical polymerization methods. Optimal conditions for acrolein polymerization are achieved using I4 as an initiator at a ratio of 1:50 to the monomer, with a monomer concentration of 7.5 mol L^-1, a reaction temperature of 50 °C, and a duration of 6 hours. Under these conditions, the yield of polyacrolein can reach up to 93.76%. The polymers formed are further characterized to confirm their structure and properties, which is essential for their potential application in various industrial fields.
The paper discusses the synthesis and characterization of polyacrolein using radical polymerization methods. Optimal conditions for acrolein polymerization are achieved using I4 as an initiator at a ratio of 1:50 to the monomer, with a monomer concentration of 7.5 mol L^-1, a reaction temperature of 50 °C, and a duration of 6 hours. Under these conditions, the yield of polyacrolein can reach up to 93.76%. The polymers formed are further characterized to confirm their structure and properties, which is essential for their potential application in various industrial fields.
Effects of Oxygen Enrichment on Supersonic Combustion in a Mach 10 Scramjet
The paper explores the effects of oxygen enrichment on supersonic combustion in scramjet engines operating at Mach 10. It discusses the benefits of premixing fuel with oxygen to enhance combustion efficiency at high altitudes where oxygen levels are otherwise insufficient. This technique aims to expand the operational envelope of scramjets, traditionally limited by atmospheric oxygen availability, thereby offering a more versatile solution for high-speed aerial and space propulsion systems.
The paper explores the effects of oxygen enrichment on supersonic combustion in scramjet engines operating at Mach 10. It discusses the benefits of premixing fuel with oxygen to enhance combustion efficiency at high altitudes where oxygen levels are otherwise insufficient. This technique aims to expand the operational envelope of scramjets, traditionally limited by atmospheric oxygen availability, thereby offering a more versatile solution for high-speed aerial and space propulsion systems.
Influence of various DEM shape representation methods on packing and shearing of granular assemblies
This paper examines how different shape representation methods influence the bulk response of granular assemblies in Discrete Element Method simulations, focusing on angle-of-repose and direct-shear tests. It considers three rolling resistance models for spherical particles and uses superquadrics and multi-spheres to model non-spherical particles like cuboids and cylinders. The study presents detailed results on how shape affects granular behavior, including comparisons of various methods. Findings from angle-of-repose tests indicate that rolling friction models effectively capture the avalanching characteristics of cube-like and cylindrical particles. Direct-shear test results highlight that only the elasto-plastic rolling resistance model accurately predicts shear strength and dilative response, although not porosity, of non-spherical particles. This research helps pinpoint optimal shape-description parameters for different representation methods.
This paper examines how different shape representation methods influence the bulk response of granular assemblies in Discrete Element Method simulations, focusing on angle-of-repose and direct-shear tests. It considers three rolling resistance models for spherical particles and uses superquadrics and multi-spheres to model non-spherical particles like cuboids and cylinders. The study presents detailed results on how shape affects granular behavior, including comparisons of various methods. Findings from angle-of-repose tests indicate that rolling friction models effectively capture the avalanching characteristics of cube-like and cylindrical particles. Direct-shear test results highlight that only the elasto-plastic rolling resistance model accurately predicts shear strength and dilative response, although not porosity, of non-spherical particles. This research helps pinpoint optimal shape-description parameters for different representation methods.
Correction: Characterization of Supersonic Turbulent Combustion in a Mach-10 Scramjet Combustor
The paper discusses modal decomposition techniques, which simplify the dynamics of fluid flows by breaking them down into fundamental components or modes. These techniques are instrumental for capturing essential dynamic features across various conditions, thereby aiding in the development of low-dimensional models for complex systems. This approach optimizes both computational and experimental methodologies in engineering and physics.
The paper discusses modal decomposition techniques, which simplify the dynamics of fluid flows by breaking them down into fundamental components or modes. These techniques are instrumental for capturing essential dynamic features across various conditions, thereby aiding in the development of low-dimensional models for complex systems. This approach optimizes both computational and experimental methodologies in engineering and physics.
Direct numerical simulation of turbulent bubbly down flow using an efficient CLSVOF method
This study uses Direct Numerical Simulations (DNS) to explore how bubbles affect turbulence in downward-flowing vertical channels. With a Reynolds number of 180, simulations are carried out for two void fractions, analyzing three bubble sizes using the Coupled Level-Set/Volume-of-Fluid (CLSVOF) method. Efficiency improvements are made with a fast pressure-correction method, allowing FFT-based solutions. Validation shows excellent accuracy, with a significant speedup of 22 times by the new solver. Results indicate bubble accumulation in the channel core, altering the mean velocity profile and reducing velocity fluctuations near the walls, while enhancing turbulence in the core. Larger bubbles increase dissipation, amplifying turbulent kinetic energy centrally.
This study uses Direct Numerical Simulations (DNS) to explore how bubbles affect turbulence in downward-flowing vertical channels. With a Reynolds number of 180, simulations are carried out for two void fractions, analyzing three bubble sizes using the Coupled Level-Set/Volume-of-Fluid (CLSVOF) method. Efficiency improvements are made with a fast pressure-correction method, allowing FFT-based solutions. Validation shows excellent accuracy, with a significant speedup of 22 times by the new solver. Results indicate bubble accumulation in the channel core, altering the mean velocity profile and reducing velocity fluctuations near the walls, while enhancing turbulence in the core. Larger bubbles increase dissipation, amplifying turbulent kinetic energy centrally.
A Novel Modeling Approach for Plastics Melting within a CFD-DEM Framework
This study introduces a novel three-dimensional modeling approach for single-screw extrusion that integrates the feed and melt sections of the process, which were traditionally considered separately. The new model, implemented within the CFDEMCoupling® framework, combines Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM) with a pioneering melting model to simulate the phase transition from solid to liquid. To validate this model, a melting apparatus was constructed and operationalized. Simulations were performed to calculate melting rates and compared with experimental outcomes, showing good alignment. This successful integration suggests the feasibility of joint CFD-DEM simulations for single-screw extruders, offering a more comprehensive analysis of the extrusion process.
This study introduces a novel three-dimensional modeling approach for single-screw extrusion that integrates the feed and melt sections of the process, which were traditionally considered separately. The new model, implemented within the CFDEMCoupling® framework, combines Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM) with a pioneering melting model to simulate the phase transition from solid to liquid. To validate this model, a melting apparatus was constructed and operationalized. Simulations were performed to calculate melting rates and compared with experimental outcomes, showing good alignment. This successful integration suggests the feasibility of joint CFD-DEM simulations for single-screw extruders, offering a more comprehensive analysis of the extrusion process.
Detection and Visualization of Splat and Antisplat Events in Turbulent Flows
The study introduces the first Lagrangian method for identifying splat and antisplat events in three-dimensional turbulent flows, where splats occur when fluid impinges on a surface, transferring energy from normal to tangential velocity components, and antisplats represent the reverse. This method employs strain tensors on flow-embedded flat surfaces to detect these events across various scales. Validated using artificial flow fields, the method was applied to analyze turbulent flow over a backward-facing step from direct numerical simulations. Results confirm the method's efficacy and reliability in identifying these events in complex flows, marking it as a valuable tool for analyzing turbulent flow dynamics.
The study introduces the first Lagrangian method for identifying splat and antisplat events in three-dimensional turbulent flows, where splats occur when fluid impinges on a surface, transferring energy from normal to tangential velocity components, and antisplats represent the reverse. This method employs strain tensors on flow-embedded flat surfaces to detect these events across various scales. Validated using artificial flow fields, the method was applied to analyze turbulent flow over a backward-facing step from direct numerical simulations. Results confirm the method's efficacy and reliability in identifying these events in complex flows, marking it as a valuable tool for analyzing turbulent flow dynamics.
A redefined energy functional to prevent mass loss in phase-field methods
The article explores an updated energy functional designed to prevent mass loss in phase-field models. The new functional includes terms that account for both bulk energy density and excess energy due to inhomogeneous distribution in the interfacial regions. This redefined energy functional helps in ensuring a proper energy balance while preventing nonphysical bulk diffusion, thus improving the conservation of mass in computational simulations that use phase-field methods.
The article explores an updated energy functional designed to prevent mass loss in phase-field models. The new functional includes terms that account for both bulk energy density and excess energy due to inhomogeneous distribution in the interfacial regions. This redefined energy functional helps in ensuring a proper energy balance while preventing nonphysical bulk diffusion, thus improving the conservation of mass in computational simulations that use phase-field methods.
Characterization of Supersonic Turbulent Combustion in a Mach-10 Scramjet Combustor
This paper discusses modal decomposition techniques as a tool for simplifying the complex dynamics of fluid flows by breaking them down into fundamental components or modes. These techniques, which include methods like Proper Orthogonal Decomposition and Dynamic Mode Decomposition, are valuable for capturing key dynamic features of fluid systems across various conditions, facilitating more efficient analysis and modeling. This approach is particularly useful in engineering and physics to develop low-dimensional models of complex systems, enhancing both computational and experimental methodologies.
This paper discusses modal decomposition techniques as a tool for simplifying the complex dynamics of fluid flows by breaking them down into fundamental components or modes. These techniques, which include methods like Proper Orthogonal Decomposition and Dynamic Mode Decomposition, are valuable for capturing key dynamic features of fluid systems across various conditions, facilitating more efficient analysis and modeling. This approach is particularly useful in engineering and physics to develop low-dimensional models of complex systems, enhancing both computational and experimental methodologies.
Numerical and experimental analysis of the extraction mechanism of an anchor plate embedded in saturated sand
Floating offshore structures often use submerged anchor plates for foundational support, requiring understanding of their extraction resistance under various conditions. Throughout their lifecycle, these foundations face complex loading from waves, tidal currents, and wind. Notably, when extracting these anchors at lifecycle’s end, their resistance significantly exceeds the combined forces of self-weight, hydrostatic, and earth pressures due to a vacuum effect as the anchor moves and increases the volume underneath, drawing in pore water. An experimental model-scale study measured pore pressures and soil movements using particle image velocimetry (PIV), exploring different extraction velocities. Additionally, numerical simulations using unresolved coupled CFD-DEM methods validated these experimental findings, enhancing understanding of anchor extraction dynamics.
Floating offshore structures often use submerged anchor plates for foundational support, requiring understanding of their extraction resistance under various conditions. Throughout their lifecycle, these foundations face complex loading from waves, tidal currents, and wind. Notably, when extracting these anchors at lifecycle’s end, their resistance significantly exceeds the combined forces of self-weight, hydrostatic, and earth pressures due to a vacuum effect as the anchor moves and increases the volume underneath, drawing in pore water. An experimental model-scale study measured pore pressures and soil movements using particle image velocimetry (PIV), exploring different extraction velocities. Additionally, numerical simulations using unresolved coupled CFD-DEM methods validated these experimental findings, enhancing understanding of anchor extraction dynamics.
Resolved and subgrid dynamics of Rayleigh–Bénard convection
This work introduces a theoretical framework for analyzing thermally driven turbulence, extending classical equations to accommodate inhomogeneous and anisotropic flows. It utilizes scale-by-scale budget equations for velocity and temperature structure functions, identifying two critical scales that delineate quasi-homogeneous and inhomogeneity-dominated ranges. Applied to large-eddy simulation, it assesses filtering effects on Rayleigh–Bénard convection dynamics. Results indicate that classic eddy-viscosity models may be inadequate for large filter lengths, suggesting alternative subgrid closures are needed. This framework offers a valuable tool for evaluating subgrid-scale models in simulations of turbulent flows.
This work introduces a theoretical framework for analyzing thermally driven turbulence, extending classical equations to accommodate inhomogeneous and anisotropic flows. It utilizes scale-by-scale budget equations for velocity and temperature structure functions, identifying two critical scales that delineate quasi-homogeneous and inhomogeneity-dominated ranges. Applied to large-eddy simulation, it assesses filtering effects on Rayleigh–Bénard convection dynamics. Results indicate that classic eddy-viscosity models may be inadequate for large filter lengths, suggesting alternative subgrid closures are needed. This framework offers a valuable tool for evaluating subgrid-scale models in simulations of turbulent flows.
Fully-resolved simulations of particle-laden viscoelastic fluids using an immersed boundary method
This study introduces a direct simulation code developed to analyze the dynamics of solid spheres in viscoelastic fluids, utilizing an open-source finite-volume solver enhanced by an immersed boundary method. This solver is designed to handle fully-resolved simulations and employs a log-conformation tensor to manage issues at high Weissenberg numbers effectively. Benchmark tests include sphere sedimentation in viscoelastic and Newtonian fluids, rotation in shear flows, and cross-stream migration in Poiseuille flow, with results validated against experimental and computational references. Additionally, the solver's accuracy in capturing phenomena like the Segré–Silberberg effect and shear-induced particle alignment was demonstrated, showing the influence of fluid rheology and confinement on particle dynamics.
This study introduces a direct simulation code developed to analyze the dynamics of solid spheres in viscoelastic fluids, utilizing an open-source finite-volume solver enhanced by an immersed boundary method. This solver is designed to handle fully-resolved simulations and employs a log-conformation tensor to manage issues at high Weissenberg numbers effectively. Benchmark tests include sphere sedimentation in viscoelastic and Newtonian fluids, rotation in shear flows, and cross-stream migration in Poiseuille flow, with results validated against experimental and computational references. Additionally, the solver's accuracy in capturing phenomena like the Segré–Silberberg effect and shear-induced particle alignment was demonstrated, showing the influence of fluid rheology and confinement on particle dynamics.
Buoyancy Effects on Turbulent Heat Transfer Behind a Backward-Facing Step in Liquid Metal Flow
Heat transfer is one the most important technical applications in fluid mechanics. Heat transfer behind sudden changes of the cross section such as a backward-facing step flow is particularly important in many devices such as the in- and outflow of thermal storage containers, collectors of power conversion systems, as well as highly heat loaded surfaces like those in concentrated solar power (CSP) plants, to name but a few examples.
Heat transfer is one the most important technical applications in fluid mechanics. Heat transfer behind sudden changes of the cross section such as a backward-facing step flow is particularly important in many devices such as the in- and outflow of thermal storage containers, collectors of power conversion systems, as well as highly heat loaded surfaces like those in concentrated solar power (CSP) plants, to name but a few examples.
Combining Open Source and Easy Access in the field of DEM and coupled CFD-DEM: LIGGGHTS®, CFDEM®coupling and CFDEM®workbench
Discrete Element Method (DEM) and its combination with Computational Fluid Dynamics (CFD-DEM) are essential for designing and optimizing particle processes in various industries such as pharmaceuticals, agriculture, and manufacturing. The open source software, CFDEM®coupling and LIGGGHTS®, offer advanced simulation capabilities. However, the complexity of installing and using these tools can be a barrier for many potential users. To address this, the commercial GUI CFDEM®workbench was developed to simplify the use of these powerful simulation tools while maintaining the benefits of open source software. It assists users in installation and setup, facilitating access to sophisticated DEM and CFD-DEM modeling in sectors ranging from steel to plastics production.
Discrete Element Method (DEM) and its combination with Computational Fluid Dynamics (CFD-DEM) are essential for designing and optimizing particle processes in various industries such as pharmaceuticals, agriculture, and manufacturing. The open source software, CFDEM®coupling and LIGGGHTS®, offer advanced simulation capabilities. However, the complexity of installing and using these tools can be a barrier for many potential users. To address this, the commercial GUI CFDEM®workbench was developed to simplify the use of these powerful simulation tools while maintaining the benefits of open source software. It assists users in installation and setup, facilitating access to sophisticated DEM and CFD-DEM modeling in sectors ranging from steel to plastics production.
Combining Open Source and Easy Access in the field of DEM and coupled CFD-DEM: LIGGGHTS®, CFDEM® coupling and CFDEM® workbench
The Discrete Element Method (DEM) and its integration with Computational Fluid Dynamics (CFD-DEM) are crucial for designing and optimizing particle processes in various industries. The open-source platforms, CFDEM®coupling and LIGGGHTS®, offer sophisticated simulation capabilities but can be complex to install. The commercial GUI, CFDEM®workbench, simplifies access by combining the advantages of open-source software with an easy setup process. This tool enables broader application of DEM and CFD-DEM modeling in industries like steel, pharmaceuticals, and food production, enhancing the practical utility of these advanced simulation technologies.
The Discrete Element Method (DEM) and its integration with Computational Fluid Dynamics (CFD-DEM) are crucial for designing and optimizing particle processes in various industries. The open-source platforms, CFDEM®coupling and LIGGGHTS®, offer sophisticated simulation capabilities but can be complex to install. The commercial GUI, CFDEM®workbench, simplifies access by combining the advantages of open-source software with an easy setup process. This tool enables broader application of DEM and CFD-DEM modeling in industries like steel, pharmaceuticals, and food production, enhancing the practical utility of these advanced simulation technologies.
Closure Development for Multi-Scale Fluidized Bed Reactor Models: A Case Study
Chemical looping reforming (CLR) processes highlight significant challenges in chemical engineering, particularly in managing transport limitations. The "NanoSim" project has developed a computational platform to address a wide range of these complexities, including diffusion in solids and nanometer-scale pores, heat and mass transfer between particles and gases, meso-scale clustering, and large-scale dispersion within a reactor. The study reveals that even at the particle scale, considerable uncertainties arise due to the spontaneous formation of meso-scale structures, which affect flow, transport, and reactions. These findings underscore the importance of accounting for these heterogeneities in CLR models to accurately predict reaction rates in industrial-scale reactors.
Chemical looping reforming (CLR) processes highlight significant challenges in chemical engineering, particularly in managing transport limitations. The "NanoSim" project has developed a computational platform to address a wide range of these complexities, including diffusion in solids and nanometer-scale pores, heat and mass transfer between particles and gases, meso-scale clustering, and large-scale dispersion within a reactor. The study reveals that even at the particle scale, considerable uncertainties arise due to the spontaneous formation of meso-scale structures, which affect flow, transport, and reactions. These findings underscore the importance of accounting for these heterogeneities in CLR models to accurately predict reaction rates in industrial-scale reactors.
What are the microscopic events of colloidal membrane fouling?
This study employs CFD-DEM simulations to analyze colloidal membrane fouling within a microfluidic system that simulates a porous microfiltration membrane. It focuses on how colloidal particles overcome energy barriers for adsorption and desorption, both between particles and with membrane surfaces. Key insights include the transition of particle interactions from the secondary to the primary minimum of the DLVO potential and the behaviors of adsorbed particles, such as re-entrainment or downstream gliding, often occurring in clusters. The pore geometry within the membrane notably influences fouling patterns. These findings lay groundwork for further exploration of the dynamics between hydrodynamic forces and surface energy effects in colloidal filtration.
This study employs CFD-DEM simulations to analyze colloidal membrane fouling within a microfluidic system that simulates a porous microfiltration membrane. It focuses on how colloidal particles overcome energy barriers for adsorption and desorption, both between particles and with membrane surfaces. Key insights include the transition of particle interactions from the secondary to the primary minimum of the DLVO potential and the behaviors of adsorbed particles, such as re-entrainment or downstream gliding, often occurring in clusters. The pore geometry within the membrane notably influences fouling patterns. These findings lay groundwork for further exploration of the dynamics between hydrodynamic forces and surface energy effects in colloidal filtration.
DEM study of mechanical characteristics of multi-spherical and superquadric particles at micro and macro scales
This study examines the mechanical characteristics of cubical particles using Multi-spheres and Superquadrics in DEM simulations via EDEM and LIGGGHTS. Initial single particle tests assess impact, interlocking, sliding, and tilting, highlighting the importance of surface bumpiness and edge sharpness. Subsequent bulk simulations include angle of repose, Jenike shear, and silo flow tests. Results demonstrate that particle shape descriptors significantly influence bulk behavior, particularly heap profiles and shear strength in dense packings. While shape features less affect flow patterns and mass flow rates in silo discharge, they crucially impact stress distribution, underscoring the importance of accurate particle modeling in DEM studies.
This study examines the mechanical characteristics of cubical particles using Multi-spheres and Superquadrics in DEM simulations via EDEM and LIGGGHTS. Initial single particle tests assess impact, interlocking, sliding, and tilting, highlighting the importance of surface bumpiness and edge sharpness. Subsequent bulk simulations include angle of repose, Jenike shear, and silo flow tests. Results demonstrate that particle shape descriptors significantly influence bulk behavior, particularly heap profiles and shear strength in dense packings. While shape features less affect flow patterns and mass flow rates in silo discharge, they crucially impact stress distribution, underscoring the importance of accurate particle modeling in DEM studies.
CFD–DEM study of residence time, droplet deposition, and collision velocity for a binary particle mixture in a Wurster fluidized bed coater
The article delves into optimizing the drying process of pharmaceutical powders using fluidized bed drying technology. It focuses on examining various parameters such as air flow rate, temperature, and particle characteristics to enhance the efficiency and uniformity of the drying process. This study is critical for improving product quality and reducing production costs in the pharmaceutical industry, where moisture content and particle integrity are crucial.
The article delves into optimizing the drying process of pharmaceutical powders using fluidized bed drying technology. It focuses on examining various parameters such as air flow rate, temperature, and particle characteristics to enhance the efficiency and uniformity of the drying process. This study is critical for improving product quality and reducing production costs in the pharmaceutical industry, where moisture content and particle integrity are crucial.
Onset of sediment transport in mono- and bidisperse beds under turbulent shear flow
The paper discusses the development and optimization of particle shape representation in DEM simulations. Traditional DEM models primarily use spherical particles due to their simplicity and computational efficiency. However, real-world applications often involve non-spherical particles, necessitating more complex modeling approaches. This paper introduces superquadric particles, which provide a more accurate representation of various particle shapes in DEM simulations, thus enhancing the model's applicability to real-world scenarios such as industrial processing and materials handling.
The paper discusses the development and optimization of particle shape representation in DEM simulations. Traditional DEM models primarily use spherical particles due to their simplicity and computational efficiency. However, real-world applications often involve non-spherical particles, necessitating more complex modeling approaches. This paper introduces superquadric particles, which provide a more accurate representation of various particle shapes in DEM simulations, thus enhancing the model's applicability to real-world scenarios such as industrial processing and materials handling.
Color-PTV measurement and CFD-DEM simulation of the dynamics of poly-disperse particle systems in a pseudo-2D fluidized bed
In this study, a novel color particle tracking velocimetry (PTV) method is developed for pseudo-2D fluidized beds, utilizing the Voronoi tracking algorithm combined with the relaxation probability tracking algorithm. This method is designed to measure velocities of differently-sized, color-marked particles. Its effectiveness is verified through synthetic images from CFD-DEM simulations, assessing factors like segmentation bias, segmentation ratio, recovery ratio, and error ratio. The color-PTV method demonstrated strong performance in tracking a large number of distinct particles in poly-disperse systems. Additionally, comparisons of experimental results with CFD-DEM simulations using various drag models revealed that simulations incorporating corrections for particle size dispersity showed markedly better alignment with experimental data in terms of mixing index, time-averaged volumetric particle flux, and velocity and granular temperature distributions among particles.
In this study, a novel color particle tracking velocimetry (PTV) method is developed for pseudo-2D fluidized beds, utilizing the Voronoi tracking algorithm combined with the relaxation probability tracking algorithm. This method is designed to measure velocities of differently-sized, color-marked particles. Its effectiveness is verified through synthetic images from CFD-DEM simulations, assessing factors like segmentation bias, segmentation ratio, recovery ratio, and error ratio. The color-PTV method demonstrated strong performance in tracking a large number of distinct particles in poly-disperse systems. Additionally, comparisons of experimental results with CFD-DEM simulations using various drag models revealed that simulations incorporating corrections for particle size dispersity showed markedly better alignment with experimental data in terms of mixing index, time-averaged volumetric particle flux, and velocity and granular temperature distributions among particles.
Accuracy and comparison of standard k-ϵ with two variants of k-ω turbulence models in fluvial applications
The paper discusses a new parametric method for aerodynamic optimization of high-speed trains, specifically focusing on reducing train wind effects. It employs a multi-objective particle swarm optimization algorithm to manage various design variables, such as the train’s cross-section, which significantly impacts its aerodynamic performance. The study also introduces a parametrization technique using the NURBS method for more flexible train body profiling. This method allows for a detailed analysis of how changes in the train's design affect its aerodynamics, aiming to optimize the streamlined shape for reduced wind resistance and improved efficiency.
The paper discusses a new parametric method for aerodynamic optimization of high-speed trains, specifically focusing on reducing train wind effects. It employs a multi-objective particle swarm optimization algorithm to manage various design variables, such as the train’s cross-section, which significantly impacts its aerodynamic performance. The study also introduces a parametrization technique using the NURBS method for more flexible train body profiling. This method allows for a detailed analysis of how changes in the train's design affect its aerodynamics, aiming to optimize the streamlined shape for reduced wind resistance and improved efficiency.
Eddy interaction model for turbulent suspension in Reynolds-averaged Euler–Lagrange simulations of steady sheet flow
The article from Elsevier discusses the effectiveness of different treatment regimens for latent tuberculosis infection (LTBI). It aims to provide evidence-based insights to assist policymakers in designing national treatment policies and protocols. The study uses the PRISMA-NMA method to review and synthesize existing data on the efficacy, adherence, and safety of various LTBI treatments, emphasizing the need for tailored approaches to prevent the progression to active tuberculosis.
The article from Elsevier discusses the effectiveness of different treatment regimens for latent tuberculosis infection (LTBI). It aims to provide evidence-based insights to assist policymakers in designing national treatment policies and protocols. The study uses the PRISMA-NMA method to review and synthesize existing data on the efficacy, adherence, and safety of various LTBI treatments, emphasizing the need for tailored approaches to prevent the progression to active tuberculosis.
Heated vertical duct flow of liquid metal with and without expansion
The effects of buoyancy on vertical duct flows with one heated side wall are investigated by means of Direct Numerical Simulations. In particular, the flow through square ducts and behind the expansion of a backward‐facing step with side walls are presented for the forced and mixed convection regime. These configurations allow studying the interaction of buoyancy forces with secondary flow of second kind in the square duct and with the shear layer and recirculation zone in case of the expansion. In both configurations, buoyancy substantially alters the mean flow field, the turbulent stresses, and the heat transfer compared to the corresponding forced convection cases.
The effects of buoyancy on vertical duct flows with one heated side wall are investigated by means of Direct Numerical Simulations. In particular, the flow through square ducts and behind the expansion of a backward‐facing step with side walls are presented for the forced and mixed convection regime. These configurations allow studying the interaction of buoyancy forces with secondary flow of second kind in the square duct and with the shear layer and recirculation zone in case of the expansion. In both configurations, buoyancy substantially alters the mean flow field, the turbulent stresses, and the heat transfer compared to the corresponding forced convection cases.
Turbulence Budgets in Buoyancy-affected Vertical Backward-facing Step Flow at Low Prandtl Number
This study uses Direct Numerical Simulation to examine the effect of buoyancy on vertical flow over a backward-facing step, particularly with low Prandtl number liquid sodium under mixed convection. It finds that buoyancy reduces recirculation, enhancing heat transfer while varying turbulence effects—decreasing it under moderate conditions and increasing it at high Richardson numbers. The study also analyzes budgets for turbulent kinetic energy, Reynolds shear stress, and heat flux components, highlighting the influence of temperature-pressure gradient correlations. This research aids in understanding liquid metal flows and improving turbulence models for such conditions.
This study uses Direct Numerical Simulation to examine the effect of buoyancy on vertical flow over a backward-facing step, particularly with low Prandtl number liquid sodium under mixed convection. It finds that buoyancy reduces recirculation, enhancing heat transfer while varying turbulence effects—decreasing it under moderate conditions and increasing it at high Richardson numbers. The study also analyzes budgets for turbulent kinetic energy, Reynolds shear stress, and heat flux components, highlighting the influence of temperature-pressure gradient correlations. This research aids in understanding liquid metal flows and improving turbulence models for such conditions.
A semi-analytical model for the effective thermal conductivity of a multi-component polydisperse granular bed
A theoretical model to predict the effective thermal conductivity of a multi-component polydisperse granular bed is presented. A simple energy balance analysis is used to arrive at an approximate analytical expression for the effective thermal conductivity. Simulation of heat transfer in a granular bed is carried out using an open source Discrete Element Method (DEM) package called LIGGGHTS. The derived analytical expressions for the effective thermal conductivity compares well with the results obtained from DEM simulations for granular beds comprising of different components with different sizes.
A theoretical model to predict the effective thermal conductivity of a multi-component polydisperse granular bed is presented. A simple energy balance analysis is used to arrive at an approximate analytical expression for the effective thermal conductivity. Simulation of heat transfer in a granular bed is carried out using an open source Discrete Element Method (DEM) package called LIGGGHTS. The derived analytical expressions for the effective thermal conductivity compares well with the results obtained from DEM simulations for granular beds comprising of different components with different sizes.
Transition between free, mixed and forced convection
The study investigates optimal conditions for producing charcoal from coconut shells, focusing on temperature and residence time's effects on charcoal yield. It includes a detailed experimental setup using a pyrolysis reactor and discusses the thermal conversion of the shells, highlighting the relationship between process parameters and the efficiency of charcoal production.
The study investigates optimal conditions for producing charcoal from coconut shells, focusing on temperature and residence time's effects on charcoal yield. It includes a detailed experimental setup using a pyrolysis reactor and discusses the thermal conversion of the shells, highlighting the relationship between process parameters and the efficiency of charcoal production.
Thermo-hydraulic flow in a sudden expansion
The article explores enhancements in DEM simulations by incorporating superquadric particles. These particles offer a more realistic representation of varied particle shapes, which is crucial for applications like materials processing and handling. This advancement allows for the simulation of complex particle interactions more accurately than traditional spherical models.
The article explores enhancements in DEM simulations by incorporating superquadric particles. These particles offer a more realistic representation of varied particle shapes, which is crucial for applications like materials processing and handling. This advancement allows for the simulation of complex particle interactions more accurately than traditional spherical models.
A resolved two-way coupled CFD/6-DOF approach for predicting embolus transport and the embolus-trapping efficiency of IVC filters
The paper introduces a resolved two-way coupled Computational Fluid Dynamics (CFD) and Six Degrees of Freedom (6-DOF) approach for simulating the movement of emboli in the cardiovascular system and evaluating the trapping efficiency of Inferior Vena Cava (IVC) filters. IVC filters are designed to prevent the passage of emboli from the lower extremities to the heart and lungs, which can cause severe complications such as pulmonary embolism. This model aims to enhance the understanding and effectiveness of IVC filters by providing a detailed simulation that includes both fluid dynamics and the filter's physical response to emboli.
The paper introduces a resolved two-way coupled Computational Fluid Dynamics (CFD) and Six Degrees of Freedom (6-DOF) approach for simulating the movement of emboli in the cardiovascular system and evaluating the trapping efficiency of Inferior Vena Cava (IVC) filters. IVC filters are designed to prevent the passage of emboli from the lower extremities to the heart and lungs, which can cause severe complications such as pulmonary embolism. This model aims to enhance the understanding and effectiveness of IVC filters by providing a detailed simulation that includes both fluid dynamics and the filter's physical response to emboli.
Heat transfer rates in sheared beds of inertial particles at high Biot numbers
This study investigates heat conduction through sheared granular materials using the ParScale solver and LIGGGHTS discrete element method. Heat transfer to the ambient fluid is modeled with a fixed coefficient, focusing on Biot and Peclet numbers as key parameters for describing heat flux. An analytical solution is provided for calculating mean particle temperature profiles, leading to a continuum model for heat flux developed through extensive simulations. Results show that low Biot numbers align with a simple model assuming uniform particle temperature, whereas higher numbers require accounting for internal temperature gradients to accurately predict heat transfer rates.
This study investigates heat conduction through sheared granular materials using the ParScale solver and LIGGGHTS discrete element method. Heat transfer to the ambient fluid is modeled with a fixed coefficient, focusing on Biot and Peclet numbers as key parameters for describing heat flux. An analytical solution is provided for calculating mean particle temperature profiles, leading to a continuum model for heat flux developed through extensive simulations. Results show that low Biot numbers align with a simple model assuming uniform particle temperature, whereas higher numbers require accounting for internal temperature gradients to accurately predict heat transfer rates.
Efficient implementation of superquadric particles in Discrete Element Method within an open-source framework
The article discusses the development and optimization of particle shape representation in DEM simulations. Traditional DEM models primarily use spherical particles due to their simplicity and computational efficiency. However, real-world applications often involve non-spherical particles, necessitating more complex modeling approaches. This paper introduces superquadric particles, which provide a more accurate representation of various particle shapes in DEM simulations, thus enhancing the model's applicability to real-world scenarios such as industrial processing and materials handling.
The article discusses the development and optimization of particle shape representation in DEM simulations. Traditional DEM models primarily use spherical particles due to their simplicity and computational efficiency. However, real-world applications often involve non-spherical particles, necessitating more complex modeling approaches. This paper introduces superquadric particles, which provide a more accurate representation of various particle shapes in DEM simulations, thus enhancing the model's applicability to real-world scenarios such as industrial processing and materials handling.
Investigating mixing and segregation using discrete element modelling (DEM) in the Freeman FT4 rheometer
The study utilizes the Discrete Element Method (DEM) to examine mixing and segregation dynamics in a Freeman FT4 powder rheometer with binary particle mixtures, focusing on varying particle size ratios and volume fractions. It finds that larger particle sizes or greater volume fractions of large particles accelerate segregation through a sifting mechanism, enhanced by higher particle velocities. Segregation intensifies radially from the center to the outer layer. Additionally, the study notes that segregation and mixing energies are influenced by frictional parameters. The FT4 rheometer's potential is highlighted for evaluating particulate materials' segregation tendencies by measuring flow energy gradients post-mixing cycles, aiding in optimizing blending operations in industrial settings.
The study utilizes the Discrete Element Method (DEM) to examine mixing and segregation dynamics in a Freeman FT4 powder rheometer with binary particle mixtures, focusing on varying particle size ratios and volume fractions. It finds that larger particle sizes or greater volume fractions of large particles accelerate segregation through a sifting mechanism, enhanced by higher particle velocities. Segregation intensifies radially from the center to the outer layer. Additionally, the study notes that segregation and mixing energies are influenced by frictional parameters. The FT4 rheometer's potential is highlighted for evaluating particulate materials' segregation tendencies by measuring flow energy gradients post-mixing cycles, aiding in optimizing blending operations in industrial settings.
Fluid and particle coarsening of drag force for discrete-parcel approach
Fine-grid Euler–Lagrange simulations were performed to study gas-fluidization of uniformly sized particles in three-dimensional periodic domains. These simulations were coarse-grained to derive filter size dependent corrections for drag laws in Euler–Euler (EE) and Multi-Phase Particle-in-Cell (MP-PIC) models. The corrections mostly stem from fluid cell coarsening rather than particle phase coarsening. This discovery indicates that drag models developed for coarse EE simulations are also applicable to MP-PIC simulations, facilitating mutual drag correction applicability between these simulation types.
Fine-grid Euler–Lagrange simulations were performed to study gas-fluidization of uniformly sized particles in three-dimensional periodic domains. These simulations were coarse-grained to derive filter size dependent corrections for drag laws in Euler–Euler (EE) and Multi-Phase Particle-in-Cell (MP-PIC) models. The corrections mostly stem from fluid cell coarsening rather than particle phase coarsening. This discovery indicates that drag models developed for coarse EE simulations are also applicable to MP-PIC simulations, facilitating mutual drag correction applicability between these simulation types.
Comparison of isotropic and anisotropic subgrid scale models in Large Eddy Simulations of a backward‐facing step and square duct flow
The present paper employs the anisotropic explicit algebraic subgrid‐stress model (EASM), proposed by Marstorp et al., developed in the spirit of an earlier explicit algebraic RANS‐model for statistical closures. The EASM in its elementary, computationally efficient non‐dynamic version is used for Large Eddy Simulation of three‐dimensional flows over a backward‐facing step at a bulk Reynolds number of 4805 and a square duct at 2205. Its performance is assessed by comparison with experimental data and an own Direct Numerical Simulation. Furthermore, a set of eddy‐viscosity models, including the recent σ‐model, is employed for comparison. Various statistical quantities are evaluated to assess the respective performance of the different models showing, that the anisotropic EASM compares favorably to the other models.
The present paper employs the anisotropic explicit algebraic subgrid‐stress model (EASM), proposed by Marstorp et al., developed in the spirit of an earlier explicit algebraic RANS‐model for statistical closures. The EASM in its elementary, computationally efficient non‐dynamic version is used for Large Eddy Simulation of three‐dimensional flows over a backward‐facing step at a bulk Reynolds number of 4805 and a square duct at 2205. Its performance is assessed by comparison with experimental data and an own Direct Numerical Simulation. Furthermore, a set of eddy‐viscosity models, including the recent σ‐model, is employed for comparison. Various statistical quantities are evaluated to assess the respective performance of the different models showing, that the anisotropic EASM compares favorably to the other models.
Buoyancy-affected backward-facing step flow with heat transfer at low Prandtl number
This paper explores turbulent upward flow of liquid metal in a vertical channel with a heated backward-facing step, pertinent to solar power plants. Direct numerical simulations assess the buoyancy effects by comparing scenarios with and without the buoyancy term, featuring a Richardson number of 0.338. The results show that buoyancy significantly alters the flow, reducing recirculation and enhancing heat transfer at the heated wall due to increased temperature advection. Detailed analysis of turbulent heat fluxes demonstrates how buoyancy modifies flow conditions. These insights help improve the physical understanding and modeling of turbulent heat transfer at low Prandtl numbers.
This paper explores turbulent upward flow of liquid metal in a vertical channel with a heated backward-facing step, pertinent to solar power plants. Direct numerical simulations assess the buoyancy effects by comparing scenarios with and without the buoyancy term, featuring a Richardson number of 0.338. The results show that buoyancy significantly alters the flow, reducing recirculation and enhancing heat transfer at the heated wall due to increased temperature advection. Detailed analysis of turbulent heat fluxes demonstrates how buoyancy modifies flow conditions. These insights help improve the physical understanding and modeling of turbulent heat transfer at low Prandtl numbers.
Highly efficient spatial data filtering in parallel using the opensource library CPPPO
CPPPO is a library developed to facilitate "scale bridging" in multi-scale approaches, integrating parallel data processing routines for both structured and unstructured Eulerian meshes, and Lagrangian data sets. It enables on-the-fly data processing, eliminating the need for storing individual simulation snapshots. Compatible with OpenFOAM®, CPPPO can also interface with other software. The library introduces an advanced parallel data filtering technique that exhibits super-linear scaling on multi-core clusters. Additionally, it offers guidelines for selecting the most effective Eulerian cell selection algorithm based on CPU core count, with demonstrated effectiveness in heat and mass transfer simulations involving dense particle beds.
CPPPO is a library developed to facilitate "scale bridging" in multi-scale approaches, integrating parallel data processing routines for both structured and unstructured Eulerian meshes, and Lagrangian data sets. It enables on-the-fly data processing, eliminating the need for storing individual simulation snapshots. Compatible with OpenFOAM®, CPPPO can also interface with other software. The library introduces an advanced parallel data filtering technique that exhibits super-linear scaling on multi-core clusters. Additionally, it offers guidelines for selecting the most effective Eulerian cell selection algorithm based on CPU core count, with demonstrated effectiveness in heat and mass transfer simulations involving dense particle beds.
Development of an unresolved CFD–DEM model for the flow of viscous suspensions and its application to solid–liquid mixing
Viscous solid-liquid mixing, crucial in industries, is often studied in turbulent regimes, but challenges persist in laminar and transitional flows. This paper discusses using multiphase CFD to examine such mixings, especially the unresolved CFD-DEM method that combines fluid dynamics with discrete element modeling to simulate large quantities of particles accurately. This study extends the method to viscous flows, exploring various momentum coupling strategies and introducing a sub-grid viscosity model to maintain correct suspension rheology. The model is applied to a stirred tank with a pitched blade turbine, and validated both qualitatively and quantitatively against experimental data, demonstrating its effectiveness in predicting particle suspension behaviors.
Viscous solid-liquid mixing, crucial in industries, is often studied in turbulent regimes, but challenges persist in laminar and transitional flows. This paper discusses using multiphase CFD to examine such mixings, especially the unresolved CFD-DEM method that combines fluid dynamics with discrete element modeling to simulate large quantities of particles accurately. This study extends the method to viscous flows, exploring various momentum coupling strategies and introducing a sub-grid viscosity model to maintain correct suspension rheology. The model is applied to a stirred tank with a pitched blade turbine, and validated both qualitatively and quantitatively against experimental data, demonstrating its effectiveness in predicting particle suspension behaviors.
Identification of DEM simulation parameters by Artificial Neural Networks and bulk experiments
This study presents a method to identify DEM simulation parameters using artificial neural networks, linking macroscopic results with microscopic parameters. An ANN is trained with varying DEM parameters to predict material behaviors, creating a database that correlates micro-level parameters with macro behaviors. This approach simplifies parameter identification for non-cohesive granular materials, requiring only one training session per experiment set to establish a generic link between experimental results and DEM parameters.
This study presents a method to identify DEM simulation parameters using artificial neural networks, linking macroscopic results with microscopic parameters. An ANN is trained with varying DEM parameters to predict material behaviors, creating a database that correlates micro-level parameters with macro behaviors. This approach simplifies parameter identification for non-cohesive granular materials, requiring only one training session per experiment set to establish a generic link between experimental results and DEM parameters.
Space and time behaviour of the temperature second-order structure function in Rayleigh-Bénard convection
The article discusses the flow structure of an under-expanded supersonic impinging (USI) jet, where the flow exits from the nozzle at a Mach number of 1 and impinges on a wall placed vertically above the nozzle. The study models the behavior and interactions at different distances, specifically focusing on a distance of five times the nozzle diameter (z/d = 5). This setup is used to observe the dynamic effects and flow patterns that result when the supersonic jet impacts the impingement surface, which is crucial for applications in aerospace and other industries requiring precise control of jet behaviors.
The article discusses the flow structure of an under-expanded supersonic impinging (USI) jet, where the flow exits from the nozzle at a Mach number of 1 and impinges on a wall placed vertically above the nozzle. The study models the behavior and interactions at different distances, specifically focusing on a distance of five times the nozzle diameter (z/d = 5). This setup is used to observe the dynamic effects and flow patterns that result when the supersonic jet impacts the impingement surface, which is crucial for applications in aerospace and other industries requiring precise control of jet behaviors.
Simulation of Flow in Multi-Scale Porous Media Using the Lattice Boltzmann Method on Quadtree Grids
The unified lattice Boltzmann model is enhanced by integrating with quadtree grids to simulate fluid flow in porous media. This model supports multi-scale flow simulation in complex systems and leverages quadtree grids for high-resolution approximation and flexible grid density control. This efficient combination is applied to calculate permeability in various systems, including fractured media, Voronoi tessellations, and computationally generated fractured shale structures. Comparisons with traditional models demonstrate its accuracy and efficiency. Specifically, it effectively distinguishes between matrix and fracture flows in shale, highlighting its utility in analyzing multi-scale porous media.
The unified lattice Boltzmann model is enhanced by integrating with quadtree grids to simulate fluid flow in porous media. This model supports multi-scale flow simulation in complex systems and leverages quadtree grids for high-resolution approximation and flexible grid density control. This efficient combination is applied to calculate permeability in various systems, including fractured media, Voronoi tessellations, and computationally generated fractured shale structures. Comparisons with traditional models demonstrate its accuracy and efficiency. Specifically, it effectively distinguishes between matrix and fracture flows in shale, highlighting its utility in analyzing multi-scale porous media.
Handling contact points in reactive CFD simulations of heterogeneous catalytic fixed bed reactors
This study focuses on the crucial role of mesh generation in Computational Fluid Dynamics (CFD) simulations, particularly for handling contact points in random packed beds of spheres. It systematically investigates the treatment of contact points in reactive gas-solid packed bed simulations, building on prior research on radial heat transfer and pressure drop. The study extends and evaluates the bridge method to surface reactions, beginning with an analysis of a regular bed of spheres under laminar conditions (Re~80). This setup allows for precise meshing at contact points, enabling explicit comparisons between meshes with and without bridges. From these comparisons, guidelines are developed and tested on the meshing of a random packed bed reactor, establishing a meshing protocol that ensures accurate descriptions of surface reactivity, pressure drops, and heat transfer in packed bed reactors.
This study focuses on the crucial role of mesh generation in Computational Fluid Dynamics (CFD) simulations, particularly for handling contact points in random packed beds of spheres. It systematically investigates the treatment of contact points in reactive gas-solid packed bed simulations, building on prior research on radial heat transfer and pressure drop. The study extends and evaluates the bridge method to surface reactions, beginning with an analysis of a regular bed of spheres under laminar conditions (Re~80). This setup allows for precise meshing at contact points, enabling explicit comparisons between meshes with and without bridges. From these comparisons, guidelines are developed and tested on the meshing of a random packed bed reactor, establishing a meshing protocol that ensures accurate descriptions of surface reactivity, pressure drops, and heat transfer in packed bed reactors.
Extended CFD–DEM for free‐surface flow with multi‐size granules
The study enhances CFD-DEM modeling with the Volume of Fluid (VOF) method to simulate free-surface flows, integrating fluid dynamics on coarse grids with particle dynamics. This approach uses an advection equation to manage liquid phase fraction and enables volume replacement between fluid and particles. A novel "porous sphere" technique allows larger particle use without losing fluid grid resolution. Validations across scenarios like dam breaks and particle sedimentation confirm the effectiveness of the new solver, cfdemSolverVOF, even with a reduced size ratio between fluid cells and particle diameter, enhancing its suitability for dynamic geotechnical applications with diverse particle sizes.
The study enhances CFD-DEM modeling with the Volume of Fluid (VOF) method to simulate free-surface flows, integrating fluid dynamics on coarse grids with particle dynamics. This approach uses an advection equation to manage liquid phase fraction and enables volume replacement between fluid and particles. A novel "porous sphere" technique allows larger particle use without losing fluid grid resolution. Validations across scenarios like dam breaks and particle sedimentation confirm the effectiveness of the new solver, cfdemSolverVOF, even with a reduced size ratio between fluid cells and particle diameter, enhancing its suitability for dynamic geotechnical applications with diverse particle sizes.
A semi-implicit immersed boundary method and its application to viscous mixing
This study addresses challenges in single-phase mixing CFD simulations caused by complex rotating geometries. A parallel semi-implicit immersed boundary method developed in Open∇FOAM for unstructured meshes is introduced. Initially validated through academic test cases, the method was applied to single-phase mixing in both baffled and unbaffled stirred tanks with a pitched blade impeller. The simulation results were benchmarked against experimental data and outcomes from single rotating frame and sliding mesh techniques. The new method demonstrated accuracy comparable to these traditional techniques in predicting flow patterns and torque values, with added ease of application to complex systems featuring multiple overlapping impellers.
This study addresses challenges in single-phase mixing CFD simulations caused by complex rotating geometries. A parallel semi-implicit immersed boundary method developed in Open∇FOAM for unstructured meshes is introduced. Initially validated through academic test cases, the method was applied to single-phase mixing in both baffled and unbaffled stirred tanks with a pitched blade impeller. The simulation results were benchmarked against experimental data and outcomes from single rotating frame and sliding mesh techniques. The new method demonstrated accuracy comparable to these traditional techniques in predicting flow patterns and torque values, with added ease of application to complex systems featuring multiple overlapping impellers.
Physical and scale-by-scale analysis of Rayleigh–Bénard convection
The article presents a novel approach to studying turbulent Rayleigh–Bénard convection (RBC) in a compound physical/scale space domain. It utilizes data from direct numerical simulations conducted in a laterally unbounded domain confined between two horizontal walls, exploring cases with a Prandtl number of 0.7 and Rayleigh numbers ranging from 1.7×10^5 to 1.0×10^7. This study offers insights into the dynamics and scale interactions within turbulent RBC, contributing valuable understanding to the field of fluid dynamics.
The article presents a novel approach to studying turbulent Rayleigh–Bénard convection (RBC) in a compound physical/scale space domain. It utilizes data from direct numerical simulations conducted in a laterally unbounded domain confined between two horizontal walls, exploring cases with a Prandtl number of 0.7 and Rayleigh numbers ranging from 1.7×10^5 to 1.0×10^7. This study offers insights into the dynamics and scale interactions within turbulent RBC, contributing valuable understanding to the field of fluid dynamics.
Hybrid parallelization of the LIGGGHTS open-source DEM code
This work presents our efforts to implement an MPI/OpenMP hybrid parallelization of the LIGGGHTS open-source software package for Discrete Element Methods (DEM). We outline the problems encountered and the solutions implemented to achieve scalable performance using both parallelization models. Three case studies, including two real-world applications with up to 1.5 million particles, were evaluated and demonstrate the practicality of this approach. In these examples, better load balancing and reduced MPI communication led to speed increases of up to 44% compared to MPI-only simulations.
This work presents our efforts to implement an MPI/OpenMP hybrid parallelization of the LIGGGHTS open-source software package for Discrete Element Methods (DEM). We outline the problems encountered and the solutions implemented to achieve scalable performance using both parallelization models. Three case studies, including two real-world applications with up to 1.5 million particles, were evaluated and demonstrate the practicality of this approach. In these examples, better load balancing and reduced MPI communication led to speed increases of up to 44% compared to MPI-only simulations.
DNS and LES of 3-D wall-bounded turbulence using Smoothed Particle Hydrodynamics
Smoothed Particle Hydrodynamics (SPH) has expanded its application to include real-world engineering scenarios, particularly in simulating turbulent three-dimensional flows. This paper highlights a significant gap in the investigation of such flows, as most SPH studies focus on the decay of isotropic turbulence without solid wall influences. The study conducts two sets of SPH simulations on turbulent channel flows. The first, a quasi-direct numerical simulation (DNS) in a reduced-size channel, tests SPH's capability as a Navier–Stokes solver without turbulence models, successfully reproducing turbulent statistics except near the wall. The second set, a large eddy simulation (LES) in a standard size channel, fails to accurately predict turbulent statistics, with failures linked to inadequate velocity-pressure interaction handling by SPH’s collocated and large stencil discretization.
Smoothed Particle Hydrodynamics (SPH) has expanded its application to include real-world engineering scenarios, particularly in simulating turbulent three-dimensional flows. This paper highlights a significant gap in the investigation of such flows, as most SPH studies focus on the decay of isotropic turbulence without solid wall influences. The study conducts two sets of SPH simulations on turbulent channel flows. The first, a quasi-direct numerical simulation (DNS) in a reduced-size channel, tests SPH's capability as a Navier–Stokes solver without turbulence models, successfully reproducing turbulent statistics except near the wall. The second set, a large eddy simulation (LES) in a standard size channel, fails to accurately predict turbulent statistics, with failures linked to inadequate velocity-pressure interaction handling by SPH’s collocated and large stencil discretization.
CFD-DEM simulation of a fluidized bed crystallization reactor
In the present study, a fluidization process in a fluidized bed crystallizer is examined using multiphase CFD-DEM (CFD: Computational Fluid Dynamics; DEM: Discrete Element Method) simulations. The simulations were carried out using the coupled open source software CFDEMcoupling. After validating the simulation results with first experimental measurements, have been used for process understanding and improvement. In particular, regions with complex flow features but important for process outcome have been identified within the crystallizer. Moreover the simulations delivered valuable information that are difficult or even impossible to measure experimentally with sufficient accuracy.
In the present study, a fluidization process in a fluidized bed crystallizer is examined using multiphase CFD-DEM (CFD: Computational Fluid Dynamics; DEM: Discrete Element Method) simulations. The simulations were carried out using the coupled open source software CFDEMcoupling. After validating the simulation results with first experimental measurements, have been used for process understanding and improvement. In particular, regions with complex flow features but important for process outcome have been identified within the crystallizer. Moreover the simulations delivered valuable information that are difficult or even impossible to measure experimentally with sufficient accuracy.
DNS of Turbulent Bubbly Downflow with a Coupled Level-Set/Volume-of-Fluid Method
Turbulent flows containing bubbles or droplets play a critical role in both industrial applications and natural processes, such as in bubble column reactors, spray combustion systems, and rain clouds. Understanding the interactions between these bubbles or droplets and the turbulent flow around them is challenging, especially when these particles are of finite size relative to the Kolmogorov scale and are present in concentrations beyond dilute conditions. The complexity of these interactions remains a significant area of research due to its implications on the efficiency and effectiveness of various systems involving multiphase flows.
Turbulent flows containing bubbles or droplets play a critical role in both industrial applications and natural processes, such as in bubble column reactors, spray combustion systems, and rain clouds. Understanding the interactions between these bubbles or droplets and the turbulent flow around them is challenging, especially when these particles are of finite size relative to the Kolmogorov scale and are present in concentrations beyond dilute conditions. The complexity of these interactions remains a significant area of research due to its implications on the efficiency and effectiveness of various systems involving multiphase flows.
Direct Numerical Simulation of turbulent heat transfer behind a backward‐facing step at low Prandtl number
The paper presents Direct Numerical Simulations of the turbulent flow of a low Prandtl number fluid over a backward‐facing step with heat transfer. The backward‐facing step flow is investigated as a generic configuration for sudden changes in cross section. Several simulations are reported: for isothermal conditions, for heat transfer with the Prandtl number of air, and for heat transfer with the Prandtl number of liquid sodium. The simulation for air is compared to results from literature. The differences induced by reduction of the Prandtl number are then assessed by comparison of the two cases. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The paper presents Direct Numerical Simulations of the turbulent flow of a low Prandtl number fluid over a backward‐facing step with heat transfer. The backward‐facing step flow is investigated as a generic configuration for sudden changes in cross section. Several simulations are reported: for isothermal conditions, for heat transfer with the Prandtl number of air, and for heat transfer with the Prandtl number of liquid sodium. The simulation for air is compared to results from literature. The differences induced by reduction of the Prandtl number are then assessed by comparison of the two cases. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Correct Boundary Conditions for Turbulent SPH
This publication discusses the formulation of correct boundary conditions for turbulent flows using the Smoothed Particle Hydrodynamics (SPH) method. It introduces unified and consistent boundary conditions for 2D SPH for weakly compressible flows, covering wall impermeability, wall shear stress, and wall turbulent conditions using the k-ε model. Additionally, it addresses inlet-outlet open boundaries, aiming to enhance the accuracy and applicability of SPH simulations in engineering and physics. This approach is crucial for modeling complex fluid dynamics in various practical and industrial applications.
This publication discusses the formulation of correct boundary conditions for turbulent flows using the Smoothed Particle Hydrodynamics (SPH) method. It introduces unified and consistent boundary conditions for 2D SPH for weakly compressible flows, covering wall impermeability, wall shear stress, and wall turbulent conditions using the k-ε model. Additionally, it addresses inlet-outlet open boundaries, aiming to enhance the accuracy and applicability of SPH simulations in engineering and physics. This approach is crucial for modeling complex fluid dynamics in various practical and industrial applications.
Review and future options for computer modelling in the sugar industry
This paper provides a review of computer modeling applications in the sugar industry over the past 25 years, highlighting both successes and challenges. It notes that while advancements in hardware and software have enhanced modeling capabilities, certain processes like cane cleaning, billet preparation, and sugar drying have seen limited improvement due to the computational intensity required to model numerous particle interactions. Despite these challenges, progress has been made in understanding these complex systems. The paper suggests employing robust commercial software with customizable subroutines or leveraging open-source software capable of utilizing large parallel computing resources to overcome computational barriers. It discusses software options that could potentially enhance efficiency and design within the industry.
This paper provides a review of computer modeling applications in the sugar industry over the past 25 years, highlighting both successes and challenges. It notes that while advancements in hardware and software have enhanced modeling capabilities, certain processes like cane cleaning, billet preparation, and sugar drying have seen limited improvement due to the computational intensity required to model numerous particle interactions. Despite these challenges, progress has been made in understanding these complex systems. The paper suggests employing robust commercial software with customizable subroutines or leveraging open-source software capable of utilizing large parallel computing resources to overcome computational barriers. It discusses software options that could potentially enhance efficiency and design within the industry.
Regimes of liquid transport through sheared beds of inertial smooth particles
This article investigates liquid transport in moving particle beds, focusing on transfer during particle collisions and convective transport due to particle motion. Simplistic models typically handle these processes, but this study evaluates various models across different flows, ultimately selecting one for detailed shear flow simulations with soft, frictional spheres. Results from these simulations help create regime maps for effective liquid flux and draw parallels to thermal energy transport, confirming the models' accuracy. These findings aim to develop continuum models for describing liquid and thermal transport through granular materials, providing a foundation for future research.
This article investigates liquid transport in moving particle beds, focusing on transfer during particle collisions and convective transport due to particle motion. Simplistic models typically handle these processes, but this study evaluates various models across different flows, ultimately selecting one for detailed shear flow simulations with soft, frictional spheres. Results from these simulations help create regime maps for effective liquid flux and draw parallels to thermal energy transport, confirming the models' accuracy. These findings aim to develop continuum models for describing liquid and thermal transport through granular materials, providing a foundation for future research.
Effects of Contact Force Model and Size Distribution on Microsized Granular Packing
The article discusses the importance of contact force models in the accurate simulation and understanding of mechanical systems where contact occurs, such as in manufacturing processes. The study analyzes different models for their effectiveness in predicting the behavior of systems at various scales, particularly focusing on the scalability and applicability of these models in real-world scenarios. This research is crucial for advancing precision in manufacturing techniques and improving the design and efficiency of mechanical assemblies and tools.
The article discusses the importance of contact force models in the accurate simulation and understanding of mechanical systems where contact occurs, such as in manufacturing processes. The study analyzes different models for their effectiveness in predicting the behavior of systems at various scales, particularly focusing on the scalability and applicability of these models in real-world scenarios. This research is crucial for advancing precision in manufacturing techniques and improving the design and efficiency of mechanical assemblies and tools.
Transfer chutes: Predicting dust emissions by multiphase CFD and coupled DEM-CFD simulations
Dust emission is one of the main problems in the operation of transfer chutes. The design of the transfer chute heavily influences any potential dust generation. Although this influence is well known, much more attention is given to active dust suppression via water spray systems, the exhaustion of the dust polluted air or the use of electrostatic filters rather than the design optimization of the transfer chute.
Dust emission is one of the main problems in the operation of transfer chutes. The design of the transfer chute heavily influences any potential dust generation. Although this influence is well known, much more attention is given to active dust suppression via water spray systems, the exhaustion of the dust polluted air or the use of electrostatic filters rather than the design optimization of the transfer chute.
Extension of a CLSVOF method for droplet-laden flows with a coalescence/breakup model
The CLSVOF method for droplet-laden flows now includes a model for droplet coalescence and breakup, enhancing its realism. This method uses unique marker functions for each droplet to avoid numerical coalescence seen in traditional methods. Coalescence is determined by a film drainage model, which activates when contact time exceeds a set threshold, merging droplet markers. Breakup is modeled by splitting these markers. Validated by simulations at various Weber numbers
The CLSVOF method for droplet-laden flows now includes a model for droplet coalescence and breakup, enhancing its realism. This method uses unique marker functions for each droplet to avoid numerical coalescence seen in traditional methods. Coalescence is determined by a film drainage model, which activates when contact time exceeds a set threshold, merging droplet markers. Breakup is modeled by splitting these markers. Validated by simulations at various Weber numbers
Investigation of wall bounded flows using SPH and the unified semi-analytical wall boundary conditions
This paper examines semi-analytical wall boundary conditions in smoothed particle hydrodynamics (SPH) for fluid flows, focusing on energy conservation and the skew-adjoint property. It reveals that exact energy conservation holds only in continuous SPH, with the discrete form approximating this, resulting in numerical "turbulence." This issue is addressed using a volume diffusion term akin to an approximate Riemann solver. Additionally, enhancements include variable driving force management in periodic flows and generalized Robin-type wall boundary conditions. Numerical experiments validate these advancements, showing significant error reduction and improved handling of free-surface flows, particularly in preventing surface detachment and optimizing interactions at walls.
This paper examines semi-analytical wall boundary conditions in smoothed particle hydrodynamics (SPH) for fluid flows, focusing on energy conservation and the skew-adjoint property. It reveals that exact energy conservation holds only in continuous SPH, with the discrete form approximating this, resulting in numerical "turbulence." This issue is addressed using a volume diffusion term akin to an approximate Riemann solver. Additionally, enhancements include variable driving force management in periodic flows and generalized Robin-type wall boundary conditions. Numerical experiments validate these advancements, showing significant error reduction and improved handling of free-surface flows, particularly in preventing surface detachment and optimizing interactions at walls.
Efficient Scalable Simulation of Burden Flow Using a Non-spherical Particle: DEM Approach
This study presents a numerical model for simulating burden flow in blast furnaces, integrating Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). The model emphasizes non-spherical particle shapes to closely replicate physical phenomena. This approach enhances the accuracy of simulations, providing valuable insights into the complex behaviors of granular materials in industrial processes.
This study presents a numerical model for simulating burden flow in blast furnaces, integrating Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). The model emphasizes non-spherical particle shapes to closely replicate physical phenomena. This approach enhances the accuracy of simulations, providing valuable insights into the complex behaviors of granular materials in industrial processes.
Modeling of wheel–soil interaction over rough terrain using the discrete element method
A numerical study utilizing the Discrete Element Method (DEM) examined the effects of rough terrain on the mobility and efficiency of small unmanned ground vehicles. The DEM simulations, validated against single-wheel test data involving straight-line motion and wheel-digging on flat soil, showed good qualitative agreement. In tests on 20 sinusoidal rough terrain profiles, mobility generally decreased, with drawbar pull dropping by up to 15% and driving torque increasing by up to 35% due to terrain-induced oscillations. The experiments used a slow speed and soft lunar regolith simulant, which minimized vertical accelerations and vehicle vibrations, thereby reducing performance impacts.
A numerical study utilizing the Discrete Element Method (DEM) examined the effects of rough terrain on the mobility and efficiency of small unmanned ground vehicles. The DEM simulations, validated against single-wheel test data involving straight-line motion and wheel-digging on flat soil, showed good qualitative agreement. In tests on 20 sinusoidal rough terrain profiles, mobility generally decreased, with drawbar pull dropping by up to 15% and driving torque increasing by up to 35% due to terrain-induced oscillations. The experiments used a slow speed and soft lunar regolith simulant, which minimized vertical accelerations and vehicle vibrations, thereby reducing performance impacts.
Decoding the structure of granular and porous materials from speckled phase contrast X-ray images
The paper discusses a new thermal lens effect utilizing a laser beam with Orbital Angular Momentum (OAM). The study investigates how the OAM properties of a laser can influence the formation of thermal lenses, a phenomenon where the medium's refractive index changes due to temperature gradients caused by laser heating. This research is significant for advancing our understanding of light-matter interactions in optically active and thermal-sensitive environments, providing insights into the dynamic processes involved and potential applications in optical systems.
The paper discusses a new thermal lens effect utilizing a laser beam with Orbital Angular Momentum (OAM). The study investigates how the OAM properties of a laser can influence the formation of thermal lenses, a phenomenon where the medium's refractive index changes due to temperature gradients caused by laser heating. This research is significant for advancing our understanding of light-matter interactions in optically active and thermal-sensitive environments, providing insights into the dynamic processes involved and potential applications in optical systems.
Application of a hybrid Lattice Boltzmann–Finite Volume turbulence model to cyclone short-cut flow
This study investigates the solubility and micronization of phenacetin using supercritical carbon dioxide. The solubility was measured at pressures from 9.0 to 30.0 MPa and temperatures between 308.0 K and 328.0 K, revealing a mole fraction solubility up to 10⁻⁵. Four density-based semi-empirical models were applied to correlate the experimental data, with the Adachi-Lu-modified Chrastil model showing the best agreement. The Rapid Expansion of Supercritical Solution (RESS) process was employed to produce fine phenacetin particles, with parameters such as extraction temperature, pressure, nozzle temperature, diameter, and collection distance influencing particle size and morphology.
This study investigates the solubility and micronization of phenacetin using supercritical carbon dioxide. The solubility was measured at pressures from 9.0 to 30.0 MPa and temperatures between 308.0 K and 328.0 K, revealing a mole fraction solubility up to 10⁻⁵. Four density-based semi-empirical models were applied to correlate the experimental data, with the Adachi-Lu-modified Chrastil model showing the best agreement. The Rapid Expansion of Supercritical Solution (RESS) process was employed to produce fine phenacetin particles, with parameters such as extraction temperature, pressure, nozzle temperature, diameter, and collection distance influencing particle size and morphology.
Discrete particle simulation of radial segregation in horizontally rotating drum: Effects of drum-length and non-rotating end-plates
DEM simulations explore the radial segregation of two different-sized grains in a horizontal rotating drum, focusing on the impact of drum length and grain-end-plate friction. Findings reveal that longer drums exhibit higher segregation ratios, with end-plate friction having minimal impact. Conversely, in shorter drums, segregation is slow or negligible, but reducing end-plate friction enhances segregation. Increasing friction beyond inter-grain and grain-wall friction decreases segregation in longer drums and promotes mixing in shorter ones. This behavior is attributed to diffusion caused by shearing strain from rougher end-plates, which raises granular temperature and leads to mixing instead of segregation.
DEM simulations explore the radial segregation of two different-sized grains in a horizontal rotating drum, focusing on the impact of drum length and grain-end-plate friction. Findings reveal that longer drums exhibit higher segregation ratios, with end-plate friction having minimal impact. Conversely, in shorter drums, segregation is slow or negligible, but reducing end-plate friction enhances segregation. Increasing friction beyond inter-grain and grain-wall friction decreases segregation in longer drums and promotes mixing in shorter ones. This behavior is attributed to diffusion caused by shearing strain from rougher end-plates, which raises granular temperature and leads to mixing instead of segregation.
Influence of rolling friction on single spout fluidized bed simulation
This study introduces a novel approach to simulate the behavior of dense particle suspensions in fluid flows. By integrating the Discrete Element Method (DEM) with Computational Fluid Dynamics (CFD), the model effectively captures particle-particle and particle-fluid interactions. Validation against experimental data demonstrates its accuracy in predicting flow patterns and particle distribution, offering a valuable tool for analyzing complex multiphase flows in engineering applications.
This study introduces a novel approach to simulate the behavior of dense particle suspensions in fluid flows. By integrating the Discrete Element Method (DEM) with Computational Fluid Dynamics (CFD), the model effectively captures particle-particle and particle-fluid interactions. Validation against experimental data demonstrates its accuracy in predicting flow patterns and particle distribution, offering a valuable tool for analyzing complex multiphase flows in engineering applications.
A comprehensive frictional-kinetic model for gas–particle flows: Analysis of fluidized and moving bed regimes
This study introduces a comprehensive frictional-kinetic model for gas–particle flows, treating both gas and particles as continua. The model integrates the kinetic theory of granular flows to account for kinetic-collisional stresses and employs inertial number-dependent rheology alongside dilation laws to represent frictional stresses. This approach effectively captures the transition between collisional and frictional regimes in dense granular flows, enhancing the accuracy of simulations in various engineering applications.
This study introduces a comprehensive frictional-kinetic model for gas–particle flows, treating both gas and particles as continua. The model integrates the kinetic theory of granular flows to account for kinetic-collisional stresses and employs inertial number-dependent rheology alongside dilation laws to represent frictional stresses. This approach effectively captures the transition between collisional and frictional regimes in dense granular flows, enhancing the accuracy of simulations in various engineering applications.
An efficient multiple marker front-capturing method for two-phase flows
This study introduces a novel approach for simulating fluid-particle interactions by integrating the Discrete Element Method (DEM) with Computational Fluid Dynamics (CFD). The authors employ an immersed boundary method to represent particles within the fluid grid, allowing for accurate modeling of complex interactions. Validation against experimental data demonstrates the model's effectiveness in predicting particle behavior in fluid flows, offering a valuable tool for engineering applications involving particulate systems.
This study introduces a novel approach for simulating fluid-particle interactions by integrating the Discrete Element Method (DEM) with Computational Fluid Dynamics (CFD). The authors employ an immersed boundary method to represent particles within the fluid grid, allowing for accurate modeling of complex interactions. Validation against experimental data demonstrates the model's effectiveness in predicting particle behavior in fluid flows, offering a valuable tool for engineering applications involving particulate systems.
Simulation of wear and dust emission at a transfer chute
In this contribution the dust emission and wear at a transfer chute is investigated by means of numerical simulations using a coupled Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD). This flexible and detailed modelling approach helps to obtain an insight into dust generation and propagation as well as wear in industrial plants. The first part of this paper deals with the optimization of a transfer chute in terms of dust emission and the second part deals with local wear prediction.
In this contribution the dust emission and wear at a transfer chute is investigated by means of numerical simulations using a coupled Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD). This flexible and detailed modelling approach helps to obtain an insight into dust generation and propagation as well as wear in industrial plants. The first part of this paper deals with the optimization of a transfer chute in terms of dust emission and the second part deals with local wear prediction.
Molecular Dynamics simulation for PBR pebble tracking simulation via a random walk approach using Monte Carlo simulation
This paper introduces a new energy functional within phase-field models to address mass conservation issues. The redefined functional helps avoid nonphysical bulk diffusion and ensures a proper energy balance, thereby improving the model's accuracy in simulating phenomena where mass loss is critical, such as in materials science and phase transitions.
This paper introduces a new energy functional within phase-field models to address mass conservation issues. The redefined functional helps avoid nonphysical bulk diffusion and ensures a proper energy balance, thereby improving the model's accuracy in simulating phenomena where mass loss is critical, such as in materials science and phase transitions.
Experimental and numerical investigation of sloshing resonance phenomena in a spring-mounted rectangular tank
Inspired by the dynamics observed in a steelmaking converter, this study examines liquid sloshing using a simplified experimental setup with a rectangular tank mounted on a spring-controlled seesaw. The experiments addressed various scenarios: a collapsing water column and gas injection-induced sloshing in both fixed and spring-mounted tanks. In spring-mounted configurations, the study highlighted that when the mechanical eigenfrequency of the suspension system aligns with the wave frequencies, a resonance occurs, leading to beat-like energy transfers that periodically increase and decrease the load on the system. These findings are supported by analytical evaluations and 3D multiphase flow simulations, which generally align with the experimental results but show artificially damped sloshing motions.
Inspired by the dynamics observed in a steelmaking converter, this study examines liquid sloshing using a simplified experimental setup with a rectangular tank mounted on a spring-controlled seesaw. The experiments addressed various scenarios: a collapsing water column and gas injection-induced sloshing in both fixed and spring-mounted tanks. In spring-mounted configurations, the study highlighted that when the mechanical eigenfrequency of the suspension system aligns with the wave frequencies, a resonance occurs, leading to beat-like energy transfers that periodically increase and decrease the load on the system. These findings are supported by analytical evaluations and 3D multiphase flow simulations, which generally align with the experimental results but show artificially damped sloshing motions.
Direct Numerical Simulation of a Buoyant Droplet Array
This research focuses on Direct Numerical Simulation (DNS) of approximately 1,000 inertial droplets in a turbulent carrier fluid, incorporating physical models for coalescence and breakup. The study addresses the computational challenges of such simulations, demonstrating that their code scales efficiently with increasing numbers of deformable droplets and larger grid sizes. This advancement enhances the understanding of droplet dynamics and turbulence interactions, particularly in clustering regimes where the Stokes number is around 1.
This research focuses on Direct Numerical Simulation (DNS) of approximately 1,000 inertial droplets in a turbulent carrier fluid, incorporating physical models for coalescence and breakup. The study addresses the computational challenges of such simulations, demonstrating that their code scales efficiently with increasing numbers of deformable droplets and larger grid sizes. This advancement enhances the understanding of droplet dynamics and turbulence interactions, particularly in clustering regimes where the Stokes number is around 1.
Improving the applicability of discrete phase simulations by smoothening their exchange fields
This study addresses the limitations of the Discrete Phase Model (DPM) in simulating particle-laden flows, particularly its inability to account for particle collisions and the resulting overestimation of particle dispersion. The authors propose an enhanced DPM approach that incorporates a stochastic collision model to simulate particle-particle interactions. Validation against experimental data demonstrates improved accuracy in predicting particle dispersion and concentration profiles, making this method more reliable for engineering applications involving particulate flows.
This study addresses the limitations of the Discrete Phase Model (DPM) in simulating particle-laden flows, particularly its inability to account for particle collisions and the resulting overestimation of particle dispersion. The authors propose an enhanced DPM approach that incorporates a stochastic collision model to simulate particle-particle interactions. Validation against experimental data demonstrates improved accuracy in predicting particle dispersion and concentration profiles, making this method more reliable for engineering applications involving particulate flows.
Spherical shock-wave propagation in three-dimensional granular packings
The article investigates the spherical shock-wave propagation in an open dense granular packing. This is studied by examining the sudden expansion of a spherical intruder within the packing. The focus is on the correlation between the geometrical structure of the granular fabric and the properties of the shock-wave as it propagates through the medium. This research is crucial for understanding the mechanical behavior of granular materials under dynamic loading, which has implications in various engineering and scientific applications.
The article investigates the spherical shock-wave propagation in an open dense granular packing. This is studied by examining the sudden expansion of a spherical intruder within the packing. The focus is on the correlation between the geometrical structure of the granular fabric and the properties of the shock-wave as it propagates through the medium. This research is crucial for understanding the mechanical behavior of granular materials under dynamic loading, which has implications in various engineering and scientific applications.
Stochastic simulation of the Uplift process for the Irish Electricity Market
In the Irish electricity market participants declare their true marginal costs and therefore the Shadow Price alone does not guarantee that generators will recover their fixed running costs. The so-called uplift complements the price and ensures that the generators recover their total costs. The aim of this paper is to review purely stochastic features of the uplift and make an attempt to simulate a new process reconstructing the original data characteristics. We propose two alternative algorithms basing on the uplift wait-jump structure as well as daily and annual seasonality. Presented results show that this kind of reconstruction is possible up to a quantitatively comparable degree.
In the Irish electricity market participants declare their true marginal costs and therefore the Shadow Price alone does not guarantee that generators will recover their fixed running costs. The so-called uplift complements the price and ensures that the generators recover their total costs. The aim of this paper is to review purely stochastic features of the uplift and make an attempt to simulate a new process reconstructing the original data characteristics. We propose two alternative algorithms basing on the uplift wait-jump structure as well as daily and annual seasonality. Presented results show that this kind of reconstruction is possible up to a quantitatively comparable degree.
A Modified Statistical Interparticle Collision Model For Colliding Particle Clouds
In this paper, a modified stochastical interparticle collision model is discussed and valdiated. A channel flow with a constriction serves as a test case. The simulation of the thereby colliding particle strands clearly shows that without the collision sub–model, the simulation with the standard Lagrangian model yields unreasonable results. After adding the stochastical collision sub–model, the Lagrangian model is able to describe the flow situation if the mass load is not too high.
In this paper, a modified stochastical interparticle collision model is discussed and valdiated. A channel flow with a constriction serves as a test case. The simulation of the thereby colliding particle strands clearly shows that without the collision sub–model, the simulation with the standard Lagrangian model yields unreasonable results. After adding the stochastical collision sub–model, the Lagrangian model is able to describe the flow situation if the mass load is not too high.
Floating electrode optoelectronic tweezers: Light-driven dielectrophoretic droplet manipulation in electrically insulating oil medium
The research introduces Floating Electrode Optoelectronic Tweezers (FEOET), a mechanism for manipulating aqueous droplets in electrically insulating oil using light-induced dielectrophoresis. FEOET employs a photoconductive glass layer to create virtual electrodes with direct optical images, enabling light-driven transport of droplets. This technique offers a versatile and efficient method for droplet manipulation in microfluidic applications.
The research introduces Floating Electrode Optoelectronic Tweezers (FEOET), a mechanism for manipulating aqueous droplets in electrically insulating oil using light-induced dielectrophoresis. FEOET employs a photoconductive glass layer to create virtual electrodes with direct optical images, enabling light-driven transport of droplets. This technique offers a versatile and efficient method for droplet manipulation in microfluidic applications.
Direct Minimization of the least-squares spectral element functional – Part I: Direct solver
The paper presents a method for solving the Helmholtz equation using spectral element methods. The authors propose a direct minimization approach to obtain the least-squares solution, aiming to improve computational efficiency and accuracy in solving this fundamental equation in physics and engineering.
The paper presents a method for solving the Helmholtz equation using spectral element methods. The authors propose a direct minimization approach to obtain the least-squares solution, aiming to improve computational efficiency and accuracy in solving this fundamental equation in physics and engineering.
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