Computational Fluid Dynamics Discrete Element Method Research Articles

Forces and grain–grain contacts in bidisperse beds sheared by viscous fluids

In a recent paper [Gonzalez et al., “Bidisperse beds sheared by viscous fluids: Grain segregation and bed hardening,” Phys. Fluids 35, 103326 (2023)], we investigated the motion of grains within a granular bed sheared by a viscous fluid and showed how segregation and hardening occur in the fluid- (bedload) and solid-like (creep) regions. In this paper, we inquire further into the mechanisms leading to grain segregation in a bidisperse bed, and how the forces are distributed. For that, we carried out numerical simulations at the grain scale by using computational fluid dynamics–discrete element method, with which we were able to track the positions, velocities, forces, and solid contacts underwent by each grain. We show that during the upward motion of large grains the direct action of fluid forces is significant in the middle and upper parts of the bedload layer, while only contact forces are significant in the creep layer and lower part of the bedload layer. We also show that in all cases the particles experience a moment about a −45° contact point (with respect to the horizontal plane) when migrating upward, whether entrained by other contacts or directly by the fluid. In addition, we show the variations in the average solid–solid contacts, and how forces caused either by solid–solid contacts or directly by the fluid are distributed within the bed. Our results provide the relationship between force propagation and reorganization of grains in sheared beds, explaining mechanisms found, for example, in river beds and landslides.

Identifying signatures of the earliest benthic bulldozers in emergent subaerial conditions during the colonization of land by animals.

The colonization of land by animals was a milestone in the history of life. Approximately 100 million years before full terrestrialization, early animals sporadically traversed emergent subaerial substrates, leaving behind trace fossils recording their activities. However, identifying temporarily emergent environments and determining the affinities, motility and subaerial endurance of the trace-makers, and the timing and magnitude of their impacts on marginal-marine environments, are challenging. Here, we used semi-resolved computational fluid dynamics-discrete element method coupling to simulate trace formation on non-cohesive sediments in submerged and emergent subaerial conditions. This revealed instability-induced morphological signatures that allow us to identify the earliest terrestrial trace fossils. Quantitative metrics enable us to infer that the putative earliest terrestrial trace-makers were molluscs, and dimensional analysis suggests that their subaerial excursions could last at least 15 min. These organisms navigated emergent environments from the early Cambrian (stage 2), tens of millions of years earlier than arthropods. This quantitative paradigm provides new insights into the palaeobiology of the earliest subaerial bulldozers and highlights that mollusc-like animals were among the first ecosystem engineers to enter marginal-marine settings. They may thus have contributed to the establishment of marginal-marine biogeochemical cycles, laying the groundwork for subsequent terrestrialization by other animals.

A hybrid scaling coarse-graining method based on a computational fluid dynamics-discrete element method

A hybrid scaling coarse-graining method based on a computational fluid dynamics-discrete element method

Three-phase CFD-DEM study on the hydrodynamics of a riser system with liquid injection

Riser reactors are frequently applied in the process industry for highly important catalytic processes. In this work, a computational fluid dynamics- discrete element method (CFD-DEM) for a riser with liquid injection was developed. This model treats the gas as a continuous phase whereas the liquid droplets and catalyst particles are treated as discrete elements. The presence of droplets causes particles to be wet, which is taken into account via coverage models of the particles. In addition, the liquid on the particles will change the collision behavior, which is included using an energy balance approach. This CFD-DEM study is conducted simulating a lab-scale pseudo-2D riser. Based on the comparison, the assumption of fully covered particles results in a significant increase in the solids holdup and clustering behavior of the riser which, especially at the low liquid flow rate, results in an over-prediction. The partial coverage simulations show that only half of the particles are covered, which has a major effect on the collisions.

Optimization of collection efficiency for a dual-row jet mining machine based on CFD-DEM coupling

Deep-sea mineral resources possess vast reserves; yet, the depositional environment is extremely harsh, and the mining challenges are significant. Overcoming the technical hurdles of deep-sea mining and protecting the marine environment to achieve sustainable development and utilization of seabed resources are major challenges in the field of marine resource development. In this work, we employ a coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) approach with the objective of enhancing the collection efficiency of deep-sea polymetallic nodules. The research focuses on adjusting and optimizing the collection parameters of a dual-jet collector. We examine the influence of the collector's jet angle and velocity on the collection efficiency. We conduct a numerical analysis of the movement characteristics of nodules, the distribution of the flow field, and the efficiency of nodule collection. The results indicate that when the rear jet angle is too small, the stripping and blocking effects on the nodules deteriorate. Conversely, when the jet angle is too large, the upwelling flow velocity decreases. The optimal collection effect is achieved with a rear jet angle of 55°. Lower jet velocities result in poorer nodule stripping, collection, and lifting. Higher jet velocities, however, increase seafloor disturbance and reduce the device's energy utilization efficiency. The collection efficiency is optimal at jet velocities ranging from 8 to 9 m/s. This research provides valuable insights for the design of high-efficiency dual-jet collector devices.

Research on the Influence of Particles and Blade Tip Clearance on the Wear Characteristics of a Submersible Sewage Pump

A submersible sewage pump is designed for conveying solid–liquid two-phase media containing sewage, waste, and fiber components, through its small and compact design and its excellent anti-winding and anti-clogging capabilities. In this paper, the computational fluid dynamics–discrete element method (CFD-DEM) coupling model is used to study the influence of different conveying conditions and particle parameters on the wear of the flow components in a submersible sewage pump. At the same time, the energy balance equation is used to explore the influence mechanism of different tip clearance sizes on the internal flow pattern, wear, and energy conversion mechanism of the pump. This study demonstrates that increasing the particle volume fraction decreases the inlet particle velocity and intensifies wear in critical areas. When enlarging the tip clearance thickness from 0.4 mm to 1.0 mm, the leakage vortex formation at the inlet is enhanced, leading to increased wear rates in terms of the blade and volute. Consequently, the total energy loss and turbulent kinetic energy generation increased by 3.57% and 2.25%, respectively, while the local loss coefficient in regard to the impeller channel cross-section increased significantly. The findings in this study offer essential knowledge for enhancing the performance and ensuring the stable operation of pumps under solid–liquid two-phase flow conditions.

Particulate transport in porous media at pore-scale. Part 1: Unresolved-resolved four-way coupling CFD-DEM

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

Coupled computational fluid dynamics-discrete element method for simulating the interactions between ship-induced waves and riprap on restricted waterway banks

In inland waterways, waves generated by passing boats cause the movement of riprap used for bank protection and stabilization. Previous studies have mainly concerned the natural channel erosion problem caused by wind-generated waves and neglected the research and findings on shipping behavior. This work presents a coupling of the computational fluid dynamics model and the discrete element method. The aim is to first study the interactions between ship waves in the confined channel and the movements of the riprap of the banks and shorelines and second to analyze the stability of these armourstones under the actions of various ship velocities and draught depths. These varying conditions exert influence on the ship-induced waves, the crucial point being the drawdown amplitude, and consequently create more intense flow behavior in the near-shore region, which results in instability and destruction of the overall structure of the armor protection layer. The higher ship velocity and the larger draught depth lead to the aggravation of instability processes of the blocs composing the protective layer. There is a critical phenomenon in the influence mechanism of vessel velocity, whereas the variation process induced by draught depth is relatively linear. In addition, the stability of the blocs also depends on their shapes, sizes, and the initial positions within the protective layer. This study could contribute to the high-quality development of inland navigation.

A compressible semi-resolved computational fluid dynamics-discrete element method coupling model for fluid–solid systems with heat transfer

A compressible semi-resolved computational fluid dynamics-discrete element method coupling model for fluid–solid systems with heat transfer

A data-driven method for fast predicting the long-term hydrodynamics of gas–solid flows: Optimized dynamic mode decomposition with control

Data-driven methods are of great interest in studying the hydrodynamics of gas–solid flows. In this paper, we developed an optimized dynamic mode decomposition with control (DMDc) method for long-term and fast prediction of one physical field with the aid of another physical field. Using the computational fluid dynamics-discrete element method (CFD-DEM) simulation results as the benchmark, the prediction ability of the standard DMDc method and the optimized DMDc method is evaluated. It was shown that the optimized DMDc method is superior when the order of magnitude of the predicted data is much larger than that of the auxiliary data, which cannot be addressed by using scaled or dimensionless data, for instance, the prediction of gas pressure with the aid of solid volume fraction; on the other hand, both DMDc and optimized DMDc methods can reasonably predict the long-term behavior of gas–solid flows, when the magnitude of the elements of the predicted field is comparative to that of the auxiliary field. This study proposes a fast and relatively accurate method for predicting the hydrodynamics of gas–solid flows with the aid of a known field.

Fluidization behavior of stirred gas–solid fluidized beds: A combined X-ray and CFD–DEM–IBM study

Stirred gas–solid fluidized bed reactors are commercially employed in polyolefin manufacturing, but the complex gas–solid contacting dynamics pose challenges in design, scale-up, and operation. In this study, the influence of agitation on the fluidization performance of Geldart B particles was investigated experimentally by X-ray imaging and pressure drop measurements and numerically by Computational Fluid Dynamics (CFD) - Discrete Element Method (DEM) - Immersed Boundary Method (IBM). The experimentally obtained minimum fluidization curve and time-averaged pressure drop show good qualitative agreement with the simulation results. Visual observations underscore that an increase in the angular velocity of the agitator results in reduced bubble size and improved bed homogeneity, as further evidenced by reduced pressure fluctuations. Furthermore, the simulations reveal that while the impeller enhances solids agitation, a proper design study is imperative, considering that static immersed bodies, such as the stirrer shaft, can adversely impact solids motion.

Research on the Collection Characteristics of a Hydraulic Collector for Seafloor Massive Sulfides

Ore collection is very important in deep-sea mining for seafloor massive sulfide (SMS). In view of the characteristics of SMS ores produced by mechanical crushing, which contain coarse particles and a wide particle size distribution, in-depth research on the collection process with a device combining a rotary crushing head and a flat suction mouth was conducted. In this paper, solid–liquid two-phase flow in the hydraulic collection process with a drum rotation is carried out using the computational fluid dynamics-discrete element method (CFD-DEM), and the flow field characteristics and particle motion characteristics are analyzed. The results indicate that particles with a maximum diameter of 20 mm can be effectively collected when the suction velocity is 3 m/s. The collection process of SMS mainly goes through three stages: particle disturbance start-up, partial particle influx, and stable collection. In addition, the appropriate drum speed facilitates the collection of SMS ore. Finally, the correctness of the numerical method was assessed using similarity experiments. This work can be used to guide the design of underwater mining equipment.

Multi-objective optimization design of a sewage pump based on non-dominated sorting genetic algorithm III

Accumulation of sanitary refuse, such as flexible cloth-like structures or the so-called rags, inflows through sewage pumps are prone to tangling, ultimately leading to clogging and wear. To prevent this, the ability of sewage pumps to handle wet wipes, rags, and similar flexible materials is a key feature that must be considered as the pumps are designed. Therefore, this paper proposed a multi-objective optimization strategy based on the fluid–structure interaction simulation, Support Vector Regression (SVR), and non-dominated sorting genetic algorithm III (NSGA-III). First, the values of the optimization objectives were obtained by a Coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) approach. Then, SVR was utilized to establish an approximate model between the design variables and the optimization objectives. The NSGA-III was applied to search the Pareto front. Finally, the improved impeller model was selected by adopting technique for order preference by similarity to an ideal solution (TOPSIS) with entropy weight. The results show that the multi-objective optimization method is suitable for the optimization design of sewage pumps. Comparing the numerical calculations of the original pump and the optimized pump, the results show that the optimized head and efficiency increased by 9.7% and 7.13%, respectively. The optimized pump improves the passage rate of the rag and effectively improves the clogging behavior. The wear amount of the optimized pump is significantly reduced by 32.54%.

CFD-DEM analysis of internal flow characteristics in multistage deep-sea mining pumps

ABSTRACT The potential profits associated with deep-sea mineral deposits have encouraged the development of new mining techniques. In particular, the effectiveness of lift pumps is crucial to the success or failure of these mining operations. In this study, the interior pressure field, turbulence characteristics, and turbulent kinetic energy of deep-sea mining pumps were numerically simulated using the computational fluid dynamics/discrete element method (CFD-DEM). Turbulence in the solid–liquid two-phase flow in deep-sea mining lift pumps was also investigated using CFD-DEM, and the key factors affecting lift and efficiency were obtained. Data exchange among particles and between particles and fluids was fully considered to obtain reliable calculation results. The results show that lift pump operation improves when the speed increases. A real-world hydraulic test was conducted to verify the simulation result. That is, increasing the speed of the lift pump stabilises the flow of particles and fluids and gradually increases the lift and efficiency. The simulation method provides a reliable starting point for developing and optimising subsea lift pumps.

Transport and clogging dynamics of flexible rods in pore constrictions.

The transport and clogging behavior of flexible particles in confined flows is a complex interplay between elastic and hydrodynamic forces and wall interactions. While the motion of non-spherical particles in unbounded flows is well understood, their behavior in confined spaces remains less explored. This study introduces a coupled computational fluid dynamics-discrete element method (CFD-DEM) approach to investigate the transport and clogging dynamics of flexible rod-shaped particles in confined pore constrictions. The spatio-temporal analysis reveals the influence of the rod's initial conditions and flexibility on its transport dynamics through a pore constriction. The simulation results demonstrate an increase in the lateral drift of the rod upon exiting the pore that can be scaled with channel height confinement. The clogging dynamics are explored based on hydrodynamic and mechanical forces, unveiling conditions for mechanical clogging through sieving. The developed method allows for the deconvolution of the forces that contribute to particle trajectories in confined flow, which is highly relevant in particle separation processes, fibrous-shaped virus filtration, biological flows, and related applications. The method is embedded into the open-source CFDEM framework, facilitating future extensions to explore multiple particle dynamics, intermolecular forces, external influences, and complex geometries.

CFD-DEM study on the raceway transport phenomena and thermo-chemical behaviors in a three-dimensional blast furnace: Effects of process parameters

An in-depth exploration of the kinetic behaviors of the raceway can provide practical insights for optimizing blast furnace (BF) operations. In this study, the transport phenomena and thermo-chemical behaviors in the raceway of a three-dimensional BF were simulated from particulate scale by using the discrete element method-computational fluid dynamics (DEM-CFD) approach. The effects of process parameters (blast velocity, oxygen concentration, blast temperature, coke size and distribution, tuyere insertion depth, and tuyere inclination) on coke combustion characteristics (mass fraction distributions of gas species and reaction kinetics rate) and thermo-chemical behaviors (particle volume fraction, raceway size, mass loss, and coke temperature) were investigated. Meanwhile, microstructures of coke bed were analyzed, and correlations were established for raceway size prediction. The results indicate that the mass fraction distributions of O2 and CO are similar, both showing balloon-like shapes. The distributions of both the CO2 mass fraction and the kinetic rates of reactions exhibit annular shapes. The raceway size increases or even overlaps with increasing blast velocity/oxygen concentration/PSD standard deviation of coke and decreasing blast temperature/coke size. Too large or too small tuyere insertion depth or tuyere inclination is not conducive to the formation of the raceway. Besides, the mass loss, temperature, and microstructures also vary with the process parameters. RSM model can well predict the raceway depth, width, and height. This study extends the particle-scale model by considering transport phenomena towards the global perspective of a real BF, and the obtained new findings on the complex reacting behaviors in the raceway will provide better insights into the optimization of the BF process.

Research on the ice-resistance performance of conical wind turbine foundation in brash ice fields

Due to the significantly higher wind energy density in high-latitude sea areas compared to other regions, the construction of offshore wind farms is shifting towards these areas. However, in high-latitude sea areas, large amounts of sea ice float on the surface during winter, making ice loads a critical factor affecting the structural safety of wind turbines. For monopile flexible wind turbines, installing an ice-breaking cone near the waterline is an effective measure to withstand the threat of sea ice. To clarify the ice resistance performance of conical wind turbine foundations in brash ice zones, this study proposes a coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM). This method is used to calculate the ice load results for a cylindrical riser, and the results were found to be in good agreement with the ice load experiment results from China University of Petroleum's wave flume (CUPWF). This validation confirms the rationality of the method. Taking a 5 MW monopile wind turbine installed with an ice-breaking cone as the research object, the time history of dynamic ice loads and the displacement response of ice-induced vibration during the interaction between the wind turbine and brash ice are simulated. Considering the water level variations caused by tides, the differences in ice resistance performance between the upright cone and the inverted cone of the ice-breaking cone are analyzed. Finally, the impact of changes in cone angle on the ice resistance performance of the wind turbine foundation is determined. The results indicate that under the impact of brash ice, the upright cone of the ice-breaking cone has a higher ice resistance capacity compared to the inverted cone. With changes in cone angle, the trends of ice loads in the horizontal and vertical directions vary oppositely. However, the overall ice resistance capacity of the wind turbine foundation decreases as the cone angle increases. This study can provide a reference for the rational design of conical wind turbines in cold regions.

Contact electrification characteristics of solid oxygen particle-laden flows in liquid hydrogen transportation

The issue of electrostatic safety in liquid hydrogen systems has garnered increasing attention, especially concerning the potential threat of electrostatic explosions due to the collision-electrification phenomenon of solid oxygen particles formed after air leakage in liquid hydrogen pipelines. To delve into the contact electrification characteristics of solid oxygen particle-laden flows in liquid hydrogen transportation, a mathematical model based on the computational fluid dynamics-discrete element method (CFD-DEM) two-phase flow dynamics has been developed. This model integrates the Hertz contact theory for describing particle collision processes and the condenser model for describing particle collision-electrification. The reliability of this model has been validated in existing literature through its ability to capture the flow characteristics of two-phase flow and the electrification characteristics of particle groups. Using density functional theory to compute the solid oxygen work function and considering the low-temperature properties of liquid hydrogen, a series of numerical studies on the flow sedimentation and electrification characteristics of solid oxygen particle-laden flows in liquid hydrogen pipelines have been conducted. The results indicate that particles carry negative charges after colliding with stainless steel pipe walls, with single charge exchange magnitudes of approximately 10−12C for particle-wall continuous collision processes and 10−14C for particle-particle collision processes, resulting in particle charge-to-mass ratios on the order of tens of μC/kg at the outlet interface. The impact of electrostatic forces on particle motion is significant and cannot be overlooked. Furthermore, the effects of velocity, particle diameter, and pipe diameter on particle charge characteristics have been thoroughly analyzed. At low flow velocities, severe particle settlement occurs, leading to increased collision frequency between particles and walls and significant charge accumulation. Increasing flow velocity can mitigate particle settlement and reduce charge levels. Changes in particle and pipe diameters have a minor impact on particle settlement but can increase single charge amounts with larger particle diameters and intensify particle charging with reduced pipe diameters due to shortened radial travel distances, leading to increased collision frequency. Our study meticulously illustrates the charge characteristics of individual particles and particle groups, providing a theoretical basis for assessing the electrostatic safety of liquid hydrogen transportation systems under extreme conditions.

Analysis of the rheological behavior of suspensions by using the Immersed Boundary Method (IBM) coupled with the Discrete Element Method (DEM)

We implemented fully resolved CFD–DEM simulations to study the rheological behavior of suspensions. Although research in this field mainly uses 2D or 3D simulations to achieve this purpose, we proposed a semi-3D model. By semi-3D models, we mean that the simulation domain contains only one layer of particles in the 3D case. Comparing results with 3D simulations revealed that this approach could significantly decrease the simulation cost while maintaining reasonable accuracy. Furthermore, we selected the Krieger–Dougherty and the Phillips models to validate the viscosity and particle migration in our simulations. We considered different volume fractions of solid particles with two different particle sizes to ensure the accuracy of our model. After successful validation, we used the fully resolved field data of shear rate and vorticity to consider the physics of particular migration in more detail. Our results confirm that our developed model could work as a particle–fluid digital twin system.

Prediction of the finished tablet coating variability in pan coaters by coupling CFD-DEM and Monte Carlo simulations: Method development and validation

We present a numerical approach to predict the long-term coating variability of tablets in pan coaters by combining coupled computational fluid dynamics-discrete element method (CFD-DEM) simulations with a Monte-Carlo method. In CFD-DEM simulations, the coater geometry, operating conditions, air flow and exact tablet shapes are directly simulated to obtain statistical distributions of tablet coating mass gain and circulation time through the spray zone. These short-term distributions (∼102 s) serve as input to a Monte Carlo (MC) method to efficiently predict the coefficient of variation in pan coaters for timescales relevant to commercial manufacture (∼104 s). These predictions achieved reasonable agreement with experimental coating thickness measurements via both the manual gauge and optical coherence tomography (OCT) from coating trials on L.B. Bohle film coaters at different scales. This method enables the application of digital tools as efficient alternatives to resource-intensive experimental trials in determining the appropriate coating process parameters.