Coupled CFD-DEM Simulation Research Articles

Coupled CFD-DEM simulation of pin-type wet stirred media mills using immersed boundary approach and hydrodynamic lubrication force

Qualitative description of stressing energies between grinding beads/media in wet stirred media mills at different operation settings could provide a comprehensive understanding of the process parameter influence. In the current work, a modeling approach for wet stirred media mills is described, employing a coupled CFD-DEM framework. This study employs an immersed boundary methodology to emulate the pin-type stirrer rotation in CFD and utilizes a hydrodynamic lubrication force to model the squeezing out and sucking in of fluid between two grinding bead surfaces. The results indicate the influence of process parameters such as the stirrer rotation speed, bead diameter, and bead filling degree. Key findings include the necessity of coupled CFD-DEM with lubrication (i.e., comparison of results from DEM, and coupled CFD-DEM simulations). Dependence of system dynamics on the fluid properties is numerically analyzed using the properties of water–glycerol mixtures.

Efficient and Low-Loss Cleaning Method for Non-Uniform Distribution of Threshed Materials Based on Multi-Wing Curved Combination Air Screen in Computational Fluid Dynamics/Discrete Element Method Simulations

During the operation of the longitudinal axis flow threshing device of a combine harvester, the threshed materials form accumulations and blockages on both sides of the screen surface, severely affecting the harvesting process. To evenly distribute the materials on the screen and solve the blockage issue, a multi-wing curved combination centrifugal fan is designed to match the mass distribution of the threshed materials. The movement mechanism of rice threshed materials in the cleaning shoe of a longitudinal axis flow combine harvester is investigated using the coupled CFD-DEM simulation method. The cleaning efficiency and performance of the traditional straight-blade fan screen device and the newly designed cleaning device are compared and analyzed, and field tests are conducted. The results show that the trajectory of the threshed materials cleaned by the device equipped with the multi-wing curved combination centrifugal fan is consistent with the mass distribution of the materials separated by the longitudinal axis flow threshing device. The absolute value of the centroid velocity of the material group in the X/Y direction is greater than that of the traditional fan, indicating that the movement speed of the particle group in the optimized fan is greater than that of the traditional fan. Therefore, in the actual cleaning process, the optimized fan’s air flow distribution more effectively accelerates the movement speed of the threshed materials, increasing the amount of materials cleaned per unit time, thereby improving the cleaning efficiency. Field comparative tests show that the designed cleaning device reduced the cleaning loss rate by up to 25.00% and the impurity content rate by 32.20%, achieving efficient and low-damage cleaning of the combine harvester. The study demonstrates the effectiveness of the proposed method for evenly distributing the materials and provides important reference for the study of other piled particle distribution systems.

Fully Coupled CFD–DEM Simulation of Oil Well Hole Cleaning: Effect of Mud Hydrodynamics on Cuttings Transport

This paper presents a coupled computational fluid dynamics–discrete element method (CFD–DEM) simulation to predict cuttings transport by the drilling fluid (mud) in different oil well drilling conditions. The mud rheology is expressed by the Herschel–Bulkley behaviour and modelled in a Eulerian framework (CFD), while the cuttings are modelled using the Lagrangian approach (DEM). In this work, the effects of drill string rotation, inclination angle, cutting size, mud rheology, and annular velocity on cleaning efficiency are investigated. It is found that increasing the well deviation from vertical to horizontal leads to a higher cuttings concentration. However, at low annular velocity, the cuttings concentration for the inclined (45-degree) annulus is found to be higher than the horizontal one due to the sliding motion of cuttings on the lower section of the annulus. Overall, the drill pipe rotation has little effect on decreasing the cuttings concentration, but the effect is more pronounced at low annular velocity.

4-way coupling CFD-DEM simulation of particle breakage and classification in a spiral jet mill: A critical analysis

Jet-milling is a particle engineering process widely adopted in industrial manufacturing to reduce the particle size of powders. Computational Fluid Dynamics simulations (CFD) coupled with Discrete Element Modelling (DEM) proved to be a valuable tool to tackle the complexity and the non-linearity of particle breakage and classification occurring in mills. To date however, they have been employed to address only single aspects of process design being unable to reproduce it completely. The coupled CFD-DEM simulations presented in this work are for the first time capable of simultaneously describe particle fragmentation, particle-gas interaction and classification. Through coarse-graining, realistic amounts of powder can be simulated allowing to demonstrate/study how the hold-up mass slows down the milling gas affecting classification and thus the milling performance. Bottlenecks/limitations of model and methodology are critically examined to understand what is currently preventing us from creating a digital twin of the milling process.

Coupled CFD-DEM simulation of interfacial fluid–particle interaction during binder jet 3D printing

The coupled dynamics of interfacial fluid phases and unconstrained solid particles during the binder jet 3D printing process govern the final quality and performance of the resulting components. The present work proposes a computational fluid dynamics (CFD) and discrete element method (DEM) framework capable of simulating the complex interfacial fluid–particle interaction that occurs when binder microdroplets are deposited into a powder bed. The CFD solver uses a volume-of-fluid (VOF) method for capturing liquid–gas multifluid flows and relies on block-structured adaptive mesh refinement (AMR) to localize grid refinement around evolving fluid–fluid interfaces. The DEM module resolves six degrees of freedom particle motion and accounts for particle contact, cohesion, and rolling resistance. Fully-resolved CFD-DEM coupling is achieved through a fictitious domain immersed boundary (IB) approach. An improved method for enforcing three-phase contact lines with a VOF-IB extension technique is introduced. We present several simulations of binder jet primitive formation using realistic process parameters and material properties. The DEM particle systems are experimentally calibrated to reproduce the cohesion behavior of physical nickel alloy powder feedstocks. We demonstrate the proposed model’s ability to resolve the interdependent fluid and particle dynamics underlying the process by directly comparing simulated primitive granules with one-to-one experimental counterparts obtained from an in-house validation apparatus. This computational framework provides unprecedented insight into the fundamental mechanisms of binder jet 3D printing and presents a versatile new approach for process parameter optimization and defect mitigation that avoids the inherent challenges of experiments.

Microscopic insights into suction bucket installation in sand: Coupled coarse-grained CFD-DEM simulations

Suction bucket foundations are being used for a wide variety of offshore foundations. However, accurate modeling of its installation remains challenging due to the complexity of soil transportation, in which the soil is typically treated as a continuum and its discrete behavior is neglected. In this paper, the bucket foundation installation in the sand under different installation methods (i.e., jacked and suction-assisted installation) is investigated from a microscopic perspective (i.e., particle scale) based on the three-dimensional coupled computational fluid dynamics (CFD) and coarse-grained discrete element method (CGDEM). It is found that the CFD-CGDEM method can successfully simulate the bucket installation process. Suction-assisted installation results in a significant reduction in the inner skirt friction resistance and end resistance, while the outer skirt friction resistance shows only a minor decrease. During suction-assisted installation, soil loosening inside the bucket contributes more significantly to the soil plug formation compared to the inflow of external soil. Compared to jacked installation, the seepage induces a significant reduction in the effective stress of soil within the interior and below the bucket tip, while it increases the effective stress outside slightly under suction-assisted installation. The work provides an alternative research approach for the suction bucket installation.

NUMERICAL ANALYSIS OF SUFFUSION BEHAVIOR UNDER CYCLIC LOADINGWITH COUPLED CFD-DEM SIMULATION

Cyclic loading has a significant effect on soil properties and seriously threatens geotechnical engineering. However, it remains unclear how cyclic loading affects the suffusion behavior in gap-graded granular soils. In this study, we performed systematic numerical simulations of suffusion in soil samples subjected to triaxial compression coupled with computational fluid dynamics (CFD) and discrete element method (DEM) approaches, i.e., coupled CFD-DEM. The proposed method is able to simulate the suffusion process in gap-graded soils under cyclic loading and reveal the evolution of the fluid fields. The suffusion of gap-graded soil samples was achieved by imposing a downward seepage flow. The results indicated that cyclic loading induces greater erosion mass and fluid velocity during the suffusion process compared to simulations under fixed external forces. The erosion curve can be divided into two stages. In the first stage, the particle loss rate is high, but only lasts for a very short period of time. Then, the particle loss rate slows down and enters the second stage. In this stage, compared to a non-vibrating sample, the sample subjected to cyclic loading still has a large eroded mass, which persists until the end of the simulation. The sensitivity analysis indicated that the first stage of suffusion is more sensitive to an increase in vibration amplitude, whereas the second stage is more responsive to an increase in frequency.

Coupled CFD-DEM simulation and experimental study of particle distribution and accumulation during tailings seepage process

The movement of tailings particles in waste rock systems under different flow rates was studied using experimental and numerical methods, aiming to provide theoretical guidance for preventing particle infiltration. The research results established a calculation relationship between pressure drop, porosity, and waste rock thickness. They also revealed the self-similarity of blockage accumulation within the waste rock. The overall study indicates that smaller particles can pass through the waste rock, but larger particles face greater difficulties. It becomes highly challenging for particles to pass through when they exceed the pore spaces between the largest waste rock particles. The distribution pattern of blockage decreases gradually from the upper part to the lower part of the waste rock pile, with proportions of blockages at different depths being 35.2%, 22.7%, 15.5%, 15%, and 11.6%. The study also examined the cumulative distribution of tailings particles passing through the waste rock under varying flow velocities (0.2 m/s, 0.3 m/s), showing that the quantity of tailings particles passing through the waste rock at 0.3 m/s is approximately 1.15 times that at 0.2 m/s. Additionally, the effectiveness of using geotextile for sealing was investigated, providing theoretical support for determining the application of waste rock particle size, thickness, and geotextile in sealing tailings particles. Moreover, understanding the self-similarity and velocity variation patterns of particles helps in selecting suitable waste rock characteristics.

Coupled CFD-DEM simulation of submarine landslide movement behavior

Submarine landslide is a common disaster geological phenomenon in the ocean, which can be destructive to underwater infrastructure. Therefore, it is necessary to simulate the evolutionary behavior of submarine viscous landslides. In this paper, computational fluid dynamics (CFD) and discrete element method (DEM) are used to establish the fluid-solid coupling model of water-particle interaction. Firstly, the inter-particle cohesion model is introduced to train the coupled CFD-DEM analysis of the kinematic evolution process, and at the same time, two typical cases are carried out to verify the analysis. In the experimental simulation, the kinematic and morphological characteristics of the submarine landslide were simulated considering the viscous effect and initial velocity of the landslide, and the influence mechanism of the landslide motion and evolution process was investigated in depth. The results show that the coupled method can better simulate the motion of submarine landslide, and the viscous effect of the landslide has a significant influence on its kinematic and morphological characteristics, and the initial velocity also significantly affects the evolution and distribution characteristics of the particle flow field of each part of the landslide in the process of motion. This study is important for the simulation and effective prediction of the kinematic evolution process of real submarine landslides.

DEM-CFD simulation and seed orientation evaluation of a self-suction wheat shooting device

Planting performance is essential for wheat sowing and seedling germination. The seed motion and sowing posture also influenced the sowing performance. In this study, a DEM-CFD coupling simulation model was conducted to investigate the seed motion characteristics in a self-suction wheat shooting device. The seed orientation and shooting angle were selected to evaluate the seed motion characteristics. The seed orientation decreased with increasing rotational speeds and gradually decreased during the seed filling and cleaning. The orientation angle increases slightly in the seed acceleration process. Specifically, the orientation angles are 19.8°, 19.1° and 18.6°, respectively, under the rotational speeds of 800, 1000 and 1200 rpm at the end of the acceleration process. The shooting angle increases with the increase of the shooting device's forward speed and rotational speed. The increase in forward speed and rotational speed increases the seed velocity. Most seed particles with shooting angles from 60° to 90°, accounted for >90% of the seed number, which depicts that the seed-filling performance is promoted with the increasing rotational speed of the blade. A validation experiment was conducted to investigate the shooting performance of the self-suction shooting device Afterward. The shooting performance, including the coefficient of variation of the shooting depth (CVSD), coefficient of variation of the seed shooting amount (CVSA) and shooting depth (SD) were analyzed. The results showed that the shooting performance of the self-suction device could fully meet the shooting requirements of winter wheat in the North China plain. Specifically, the CVSD, CVSA and SD were 5.2%, 5.3% and 31.2 mm, respectively, under the rotational speed of 1200 rpm. The approach is providing a new sustainable and noncontact method for sowing wheat.

Study on heterogeneous gas-solid structure and interparticle collision behavior in a vibrated fluidized bed of Geldart D particles using CFD-DEM simulations

The spatiotemporal characteristics of the heterogeneous gas-solid structure and interparticle collisions in fluidized beds of Geldart D particles with and without vibration were comparatively studied by the coupled CFD-DEM simulations. The effects of vibration on the spatiotemporal distributions of particle configuration and particle dynamics were revealed utilizing data visualization and frequency domain analysis. The results show that the input vibration facilitates the formation of square-nosed slugs and improves the uniformity of gas-solid contacts. Moreover, vibration causes fluctuations in static air pressure on the entire bed simultaneously. It is revealed that the introduction of vibration can significantly increase the intensity and uniformity of interparticle collisions, the number of particles involved in collisions, and the total kinetic energy of the bed. The results also show that there exists a positive correlation between average collision number and solid volume fraction while an inverse correlation between granular temperature and solid volume fraction.

Multi-modal framework to model wet milling through numerical simulations and artificial intelligence (part 1)

Stirred media mills are used in many industries from mechanochemistry, to ore crushing, battery production and pharmaceutics. Investigation and modelling can be a costly, difficult and time consuming endeavour, limiting the investigable parameter space with some aspects only being accessible via numerical methods such as simulations or artificial intelligence (AI). Simulations allow investigations of inner mechanisms and generate large quantities of data while being computationally demanding. AI requires large data quantities yet is applicable with limited computing power for large parameter spaces. For this reason, the intelligent integration of different methods holds great promise to achieve maximum benefits at minimum cost by synergistically combining respective advantages. Here, a multi-modal framework is demonstrated, combining experiments, simulations and AI. In this first paper direct magnetic measurements via a tracer particle are compared with simulations of wet mills. With two way coupled CFD-DEM simulations inner mechanisms like the impact of disc geometry, tip speed and grinding bead size are investigated. Differences in translational and relative velocity distributions are investigated, showing a consistent displacement of a factor three toward higher energies throughout the complete distribution for the hole disc in comparison to the full disc, and less consistent deviations for translational velocity, specifically for the higher energy collisions, being larger by a factor of 8. Also comparisons with the existing mechanistic model of Kwade are performed. An additional indirect influence of diameter on tip speed could be detected. In a second publication AI modelling will be performed on the basis of the simulations.

Coupled thermo-hydro-mechanical-chemical modeling of fines migration in hydrate-bearing sediments with CFD-DEM

Fines migration associated with the multiphase flow in the exploitation of hydrate-bearing sediments (HBS) usually induces local clogging and sand production around wells, and thus its behavior with multi-field coupling is of vital importance but still poorly discovered. This paper establishes a coupled thermo-hydro-mechanical-chemical (THMC) model incorporating fines migration in HBS from micro- to macro-scale. Two typical hydrate pore habits, i.e., grain coating and pore filling, are simulated with the discrete element method (DEM) under different depressurization modes, water flow is simulated using computational fluid dynamics (CFD), and heat transfer and chemical reactions are also considered in coupled CFD-DEM simulations. Two distinct fines migration modes and their consequence on the mechanical and hydromechanical properties are revealed. For the grain-coating habit, the coarse particle size reduction induced by hydrate dissociation under an intense depressurization decreases the constriction size, increasing the local pore-clogging probability and reducing the growth rate of the hydraulic conductivity. Conversely, the fine particle size reduction in the pore-filling habit facilitates fines migration and thus sand production, with hydromechanical properties of HBS evolving oppositely compared to the clogging case.

Micromechanical analysis of capillary suction effect on bearing capacity of unsaturated fine granular foundation soil using coupled CFD-DEM method

The micro- to macro-scale bearing capacity characteristics of unsaturated fine granular soil have remained unclear. This study is the first to investigate the capillary suction effect on the bearing capacity of unsaturated fine granular soil in a plate load test via a series of coupled CFD-DEM simulations. The bearing capacities of fine granular soils in dry, unsaturated and saturated conditions are compared at both the macro- and microscales. The findings reveal that in addition to sharply improving the bearing capacity, capillary suction is useful for increasing allowable settlement in fine granular soil. Moreover, the study uncovers a much deeper particle migration as well as a much larger triangular zone of contact force distribution in the unsaturated soils compared to saturated soils. The existence of a huge triangular rigid zone under the plate in unsaturated fine granular soil is the major reason behind the high soil bearing capacity, and the capillary suction effect is partly similar to the surcharge effect on soil bearing capacity, leading to an explanation of this phenomenon in a micro-scale context.

A coupled CFD-DEM simulation of fracture sealing: Effect of lost circulation material, drilling fluid and fracture conditions

Lost circulation could be one of the most troublesome and expensive situations during drilling, especially in naturally fractured formations. Sealing fractures by granular lost circulation materials (LCMs) is one of the common methods for lost circulation control. However, this type of LCM has a limited effectiveness partly due to the poor understanding of how granular LCMs work. To fill this gap, a coupled CFD-DEM model is utilized for simulating the sealing process of a typical granular LCM (calcium carbonate) in a wedge-shaped fracture. In this paper, we first defined a set of comprehensive evaluation criteria for the sealing performance of LCMs, which include sealing probability, sealing time, location and stability of the seal, total loss volume and pressure gradient within the sealing zone. Effects of LCM, base fluid and fracture geometry on the sealing performance were investigated using the above-mentioned criteria based on differential pressure buildup, cumulative loss volume, and LCM loss rate, and differential pressure along depth. Our results show that LCM bridging and sealing in the fractures are initialed and controlled under interactive fluid-particle forces (drag force, viscous force and pressure gradient force), contact forces (normal and tangential) and friction forces (static and sliding). Essentially, it is the fluid-particle interactions, ratio of particle size to fracture width, volume concentration and friction effect that determine the fracture sealing performance. For the 1 mm–0.34 mm wedge-shaped fractures, sealing by LCM suspension with particle volume concentration of 9%, the critical bridging and sealing particle size are 200 μm and 330 μm, respectively. For the base simulation case considered in this paper, the critical bridging concentration and the sealing initiation concentration are both between 5% and 7%, and the critical sealing concentration is ranging between 7% and 9%. The critical coefficient of friction between particles for a stable fracture sealing varies between 0.2 and 0.4, and the critical coefficient of friction between particles and fracture surface for stable fracture sealing is ranging between 0 and 0.2. The critical Young’s modulus of particles for dual-particle bridging is between 0.1 and 1 GPa. The critical fluid injection rate is ranging between 1.25 and 3 m/s beyond which the LCM cannot seal the fracture. The rest of factors affect LCM bridging and sealing by changing these four factors to some extents. Particle size, volume concentration, Young’s modulus and the coefficient of friction of bridging granular LCM, and density, viscosity and injection rate of base fluid should be optimized synergistically to achieve an efficient fracture sealing. This research provides a better insight into the working principle of LCMs, which gives a solid scientific basis for LCM selection and design in practical problems.

A noncontact self-suction wheat shooting device for sustainable agriculture: A preliminary research

In this study, a noncontact self-suction wheat shooting device was developed through TRIZ theory to improve seed-filling performance and eliminate the contact between seed and device. A preliminary suction experiment was developed using FLUENT to simulate airflow velocity and evaluate the feasibility of self-suction performance of seeds. The DEM-CFD coupling simulation experiment was conducted to investigate the shooting performance. The simulation results showed the airflow velocity was over 6.5 m/s while rotational speed was more than 800 rpm, which could meet the seed-filling requirements. With the rotational speed increase, seed velocity and seed filling performance improves. On the contrary, a larger rotational speed and installation angle induced a higher CF (contact force). CF was significantly affected by rotational speed, window length and installation angle. The increasing window length resulted in the improvement of seed filling performance in a certain range. Meanwhile, the indicators of coefficient of variation for seeding uniformity (CVSU), coefficient of variation for seeding depth (CVSD) and seed damage rate (DR) were evaluated to investigate sowing performance of self-suction shooting device in validation experiment. Results from bench and field experiment showed the seed-filling and shooting performance of self-suction shooting device under optimized operation parameters could fully meet the sowing requirement of winter wheat in North China plain. The collision performance between seed and blades of optimized self-suction shooting device was superior to the mechanical one. In specific, CVSU, CVSD, ASD, ASS and seed germination rate of optimized self-suction shooting device were 11.3%, 8.7%, 31.0 m/s, 30.1 mm and 89.2%, respectively.

Measurement and Calibration of the Discrete Element Parameters of Coated Delinted Cotton Seeds

To simulate the interactions between a pneumatic cotton precision seed-metering device and coated delinted cotton seeds accurately, physical and simulation experiments based on a rotating drum apparatus were combined to calibrate the discrete element simulation parameters of E`kangmian-10 cotton seeds. Firstly, the contact parameters and the dynamic repose angle of the cotton seeds were measured through physical tests. Based on the particle size requirement of the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) coupling simulation and the reverse engineering technology, the cotton seed discrete element bonded-particle model (BPM) was established. Secondly, taking the contact parameters as calibration objects and the simulated dynamic repose angle as the evaluation index, a Plackett–Burman (PB) test was designed for significance screening. The results of the screening test showed that the static friction coefficient of cotton seed–tough photosensitive resin, the impact recovery coefficient of cotton seed–cotton seed, and the static friction coefficient of cotton seed–cotton seed had a highly significant effect on the simulated dynamic repose angle. Next, a Box–Behnken Design (BBD) test was adopted to establish the quadratic regression model between significant parameters and the simulated dynamic repose angle, and then the multi-factor optimization solution was carried out to obtain the optimal combination of parameters: the static friction coefficient of cotton seed–tough photosensitive resin and the impact recovery coefficient and static friction coefficient of cotton seed–cotton seed were 0.33, 0.06 and 0.10, respectively. Lastly, verification tests on the rotating drum apparatus and the seed-metering device were performed, and their relative errors were less than 2%, which indicated that the discrete element models and the contact parameters of the coated delinted cotton seeds were reliable. This study provides a reference for the selection of the discrete element parameters of coated delinted cotton seeds for DEM-CFD coupling simulation and the optimal design of precision seed-metering device for cotton.

Predicting the permeability coefficient of polydispersed sand via coupled CFD–DEM simulations

Permeability is one of the most fundamental properties of soil, which governs many geotechnical engineering problems. However, among the published equations that predict the permeability coefficient k, the influence of a wide range of particle size distributions (PSDs) on k was not considered accurately. This research aims to quantify the influence of PSD on k and propose a prediction equation for k. Coupled computational fluid dynamics–discrete element method (CFD–DEM) simulations were conducted to reproduce the constant head permeability tests of different soil samples. The results show that among the various drag models implemented in the CFD–DEM, the Syamlal–O’Brien drag model leads to the highest accuracy in simulating sand permeability. The permeability coefficient is proportional to the square of the Sauter mean diameter of the polydispersed particle system. Therefore, the prediction equation for k considering the PSD of the particle system is proposed based on the particle gradation and the size characteristics Cu, Cc, and d10. The proposed equation is verified well by published experimental data. Additionally, the proposed equation can calculate the k of irregular calcareous sand by representing the effect of particle irregularity with the Kozeny–Carman (KC) constant.

Coupled CFD-DEM Simulations for Modelling Non-Spherical Particles

Coupled CFD-DEM Simulations for Modelling Non-Spherical Particles

Numerical and experimental investigation into gas flow field and spattering phenomena in laser powder bed fusion processing of Inconel 718

Accumulated spatters not only deteriorate the quality of the built parts in terms of surface roughness and/or density but also sabotage the whole fabrication process via damaging the powder re-coater. A cross-flow of inert gas inside the processing chamber is by far the only effective mean of removing the spouted spatters from the build platform. Despite the essential role, there are few efforts to investigate the interactions between the cross-flow dynamics and the spouted spatters, and hence, to optimize the design and settings of the cross-flow. Therefore, in this study, a coupled computational fluid dynamics (CFD) – discreate element method (DEM) simulation framework is proposed to study the interactions between the flow field and the spouted spatters during the single scan process. The simulation results for the maximum ejection distance and maximum ejection height of the spatters were shown to deviate from the numerical results reported in the literature by no more than 15%. Moreover, the simulation results for the distribution of the landing sites of the spatters were consistent with the experimental observations, which showed that a large number of large spatters landed near the scan track, while a small number of large spatters landed at a greater distance from the scan track. To the best of the authors’ knowledge, this study represents the first reported attempt to use a coupled CFD-DEM simulation framework to investigate the spatter dynamics within an LPBF chamber and to validate the results with experimental observations and published data. The proposed model is an important tool to optimize and calibrate the cross-flow inside the L-PBF processing chamber.