Computational Fluid Dynamics Discrete Element Method Simulation Research Articles

Resolved CFD-DEM simulation of blood flow with a reduced-order RBC model

Mathematical modeling of the blood flow with a resolved description of biological cells mechanics such as red blood cell (RBC) has been a challenge in the past decades as it involves physical complexities and demands high computational costs. In the present study, we propose an approach for efficient simulation of blood flow with several suspended RBCs. In this approach, we employ our previously proposed reduced-order model for deformable particles (Nair et al. in Comput Part Mech 7:593–601, 2020) to mimic the mechanical behavior of an individual RBC as a cluster of overlapping spheres interconnected by flexible mathematical bonds. This discrete element method-based model is then coupled with a fluid flow solver using the immersed boundary method with continuous forcing in the context of computational fluid dynamics-discrete element method (CFD-DEM) coupling. The present computational method is tested with a couple of validation cases in which the single RBC dynamics, as well as the blood flow with several RBCs, were tested in comparison with existing literature date. First, the RBC deformation index in shear flow at different shear rates is studied with a good accuracy. Then, the blood flow in micro-tubes of different diameters and hematocrits was simulated. The key characteristics of blood flow such as cell-free layer (CFL) thickness, Fahraeus effect and the relative apparent viscosity are used as the validation metrics. The proposed approach can predict the formation of the migration of RBC toward the tube center-line and the CFL thickness in good agreement with previous measurement and simulations. Furthermore, the model is employed to study the CFL enhancement for plasma separation based on channel constriction. The simulation results compute the CFL thickness downstream of the channel constriction in good agreement with the experiments in a wide range of flow rates and constriction lengths. The original contribution of this study lies in proposing an efficient resolved CFD-DEM simulation method for blood flows with many RBCs which can be employed for numerical investigation of bio-microfluidic applications.

Computer simulation of the effect of particle stiffness coefficient on the particle-fluid flows

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective stiffness coefficient of particles for CFD-DEM simulations. The comparisons of the results indicate that although the application of stiffness coefficients with moderate values causes normal penetration depths of up to the particle radius, the simulations still show good results. The results also show that the stiffness coefficient and time step are strongly dependent of the fluid inlet velocities, particle diameters, particle inlet concentration and fluid type, and the simulation accuracy decreases greatly with increasing the time steps.

Numerical and experimental validation of a detailed non-isothermal CFD-DEM model of a pilot-scale Wurster coater

Even though the Wurster technology is commonly used in the pharmaceutical industry for applying coating to beads, additional research work is still necessary to fully understand and control the process. Various simulation approaches have been used extensively in the recent years to investigate different fluidized beds, with and without spray application. The Computational Fluid Dynamics- Discrete Element Method (CFD-DEM) coupled approach is especially suitable to simulate the coating process because it resolves both the fluid and granular flow, and provides detailed particle-scale information.This paper primarily highlights the ability of the CFD-DEM coupled code to capture the thermodynamics and water mass loading of the gas phase in the Wurster coating application by directly comparing the experimental results with the CFD-DEM simulation results, for four different experimental runs and unscaled particle size. It also reports on the four specially designed experiments, giving the measurements of the air temperature and humidity at four points in the coater.The code is verified as well, using a simple simulation test case, with the objective of ensuring the energy and mass conservation in the CFD-DEM communication protocol.The paper also presents the time-averaged contour plots of temperature, humidity and particle volume fraction distribution for four different experiment/simulation cases and provides insights into their spatial distribution in the Wurster coater.

CFD-DEM Simulation of Spouted Bed Dynamics under High Temperature with an Adhesive Model

Particle adhesion is of great importance to coating processes due to its effect on fluidization. Currently, Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) has become a powerful tool for the study of multiphase flows. Various contact force models have also been proposed. However, particle dynamics in high temperature will be changed with particle surface properties changing. In view of this, an adhesion model is developed based on approaching-loading-unloading-detaching idea and particle surface change under high temperature in this paper. Analyses of the adhesion model are given through two particle collision process and validated by experiment. Effects of inlet gas velocity and adhesion intensity on spouted bed dynamics are investigated. It is concluded that fluidization cycle will be accelerated by adhesion, and intensity of fluidization will be marginally enhanced by slight adhesion. Within a certain range, increasing inlet gas velocity will lead to strong intensity of particle motion. A parameter sensitivity comparison of linear spring-damping model and Hertz-Mindlin Model is given, which shows in case of small overlaps, forces calculated by both models have little distinction, diametrically opposed to that of large overlaps.

Performance evaluation of standard cyclone separators by using CFD–DEM simulation with realistic bio-particulate matter

As an abatement emissions control and energy-consuming device, cyclone separators are the most common device used in bioprocessing to separate fine and coarse particulate matter (PM) from the gas flow. In this investigation, four standard cyclones geometries viz. 1D2D, 2D2D, 1D3D, and 1D3D with 2D2D inlet (1D3D/w2D2D) in addition to a designed one, were simulated to investigate the performance characteristics. The D's refers to the cyclone diameter, and the numbers before each D's relate to the length of the cylindrical and conical sections, respectively. The PM used for testing and modeling was conducted on two types of real heterogeneous bioparticles (jojoba seeds and their leaves). This research is considered the first head start approach to predict the cyclone performance under the true shape modeling of PM. Discrete Element Method (DEM) was employed to simulate the trajectory of each particle, taking into consideration the interactions and collisions. Simultaneously, the Computational Fluid Dynamics (CFD) was used to simulate the highly curved streamlines and the chaotic turbulence of the continuum airflow with the Reynolds stress turbulence model (RSM). The designed cyclone was used to validate the results, which showed a good agreement between simulated data and the experimental work. The result showed that the 1D2D cyclone design has a better performance than that of the other cyclones. The methods used in this work for analyzing the phenomena occurring inside the cyclone separator allow for the conclusion that cyclone performance not only varies significantly with the cyclone type but the operating conditions as well. With these presented characteristics and evaluations, industrialists can utilize the mentioned designs for different processing to get high performance using a coarse and large PM process.

Semi-coupled resolved CFD–DEM simulation of powder-based selective laser melting for additive manufacturing

We present a semi-coupled resolved Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) to simulate a class of granular media problems that involve thermal-induced phase changes and particle–fluid interactions. We employ an immersed boundary (IB) method to model the viscous fluids surrounding solid particles in conjunction with a fictious CFD domain occupied by the actual positions of the particle. Heat transfers between the actual fluids and the fictitious particle are treated as a multiphase problem by the CFD to resolve the temperature gradient distribution within each granular particle and its possible phase change (e.g., melting or partial melting). The mechanical interactions between the solid particles and the fluids are modeled by coupled DEM and CFD. The proposed method is validated by simulations of a typical powder-based selective laser melting (PB-SLM) process. Three key SLM input parameters, laser power, laser energy distribution and hatch distance, are examined on the effect of melting. The simulation results capture key features and observations of PB-SLM found in experiments and are quantitatively consistent with available testing data. The study provides a physically based, high-fidelity computational approach for future PB-SLM additive manufacturing.

True shape modeling of bio-particulate matter flow in an aero-cyclone separator using CFD–DEM simulation

The multi-phase flow of air and bio-particulate matter exists in many biological and environmental systems such as aerodynamic separating devices, fluidized bed combustion, and feed processing machinery. Integration of the computational fluid dynamics (CFD) and discrete element method (DEM) codes was performed to study bio-particle loading ratios' effect on the cyclone device performance. Every individual particle's behavior was captured by a DEM model using Newton’s equations of motion, in which CFD modeled the continuum airflow for every computational cell scale through the Navier–Stokes equation. According to the high turbulence and chaotic behavior of the continuum airflow inside the cyclone separator, Reynolds stress turbulence model (RSM) was used. The particles used for testing and modeling were conducted on two mixture types of real-heterogeneous particulate matter, namely jojoba seeds and jojoba leaves, without any fly ash. The particles were geometrically modeled using their actual dimensions and shapes, considered the first head start research approach in the cyclonic separation and purification field. The influence of the interacting particle–particle and particle–boundary forces was taken into consideration. The numerical simulation results successfully predicted the cyclone performance at the designed conditions, which showed the best experimental data trend. These data are useful in future studies to modify the cyclone design and optimize bio-systems' operating conditions for separating the macroscopic particulate matter.

Experiments and CFD-DEM simulations of fine kaolinite particle sedimentation dynamic characteristics in a water environment

Fine kaolinite particles are mineral particles that are found in mine wastewater. The particles' shape is one of the parameters that causes a significant change in the sedimentation dynamics in water environments. In this work, experimental methods and Computational Fluid Dynamics - Discrete Element Method (CFD-DEM) methods served to investigate the dynamic characteristics of fine kaolinite particle sedimentation. The Results of statistical analyses show that the length-width ratio of fine kaolinite particles is 1–3 and the average simplified spherical coefficient is 0.625 in the 50–500 μm particle size range. The simplified spherical coefficient formula proved to be effective according to experimentation and simulations. Moreover, the effects of particle size, liquid viscosity, and liquid velocity on kaolinite particle sedimentation dynamic characteristics were numerically studied in detail by using the modified spherical coefficient. The simulation revealed that an increase in liquid viscosity resulted in a declining particle terminal velocity. However, the sensitivity of the particle terminal velocity affected by liquid viscosity fell when the particle size also declined. When an increase in particle size occurred, the sensitivity of the particle terminal velocity to the influence of upwelling water decreased.

CFD-DEM simulation of Small-Scale Challenge Problem 1 with EMMS bubble-based structure-dependent drag coefficient

In this study, the energy minimization multi-scale (EMMS)/Bubbling model is coupled with the computational fluid dynamics/discrete element method (CFD-DEM) model via a structure-dependent drag coefficient to simulate the National Energy Technology Laboratory (NETL) small-scale challenge problem using the open-source multiphase flow code MFIX. The numerical predictions are compared against particle velocity measurements obtained from high-speed particle image velocimetry (HSPIV) and differential pressure measurements. The drag-reduction effect of the EMMS bubble-based drag coefficient is observed to significantly improve predictions of the horizontal particle velocity and granular temperature when compared to several other drag coefficients tested; however, the vertical particle velocity and pressure fluctuation characteristic predictions are degraded. The drag-reduction effect is characterized by a reduction in the sizes of slugs or voids, as identified through spectral decomposition of the pressure fluctuations. Overall, this study shows great promise in employing drag coefficients, developed via multi-scale approaches (such as the EMMS paradigm), in CFD-DEM models.

Determination of the physical and interaction properties of sorghum grains: Application to computational fluid dynamics–discrete element method simulations of the fluid dynamics of a conical spouted bed

Computational simulation is an important tool for design and improvement of industrial units. Computational fluid dynamics (CFD) coupled with the discrete element method (DEM) has been applied to simulate drying equipment that usually involves gas–solid flow. For reliable results of CFD–DEM simulations, the properties related to the interactions of the material within the industrial equipment, such as the restitution or friction coefficients, must be known. In this study, CFD–DEM was applied to simulate the fluid dynamics inside a conical spouted bed operating with sorghum grains. The physical properties of the particulate phase and the particle–particle and particle–wall interaction parameters were determined by the direct measurement approach and applied to CFD–DEM. The interaction parameters were experimentally determined, including the particle–particle interaction parameters of η=0.46, μS=0.79, and μR=0.70, and the particle–wall interaction parameters of η=0.56, μS=0.75, and μR=0.40. The simulated minimum spouting velocity and characteristic curves were compared with the experimental results. There was good agreement between the simulated and experimental results.

Effects of liquid property on onset velocity of circulating fluidization in liquid-solid systems: A CFD-DEM simulation

Knowledge on regime transition from conventional to circulating fluidization is important to scale-up and operation of liquid-solid fluidized systems in industrial applications. Previous experimental studies reported that the onset velocity measured by bed empty time test is pertinent to the physical properties of particle and liquid, and independent of solid inventory, bed geometry, and configuration. The effect of liquid properties is, however, not clear yet since tap water is usually used as the working fluid in laboratory test for convenience. To address this problem, a Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) model is applied to numerically measure the onset velocity of particles in different liquid media. The model is first validated in terms of the experimental data of bed expansion in literature. Then several kinds of particles and three kinds of liquid media of different densities and viscosities are further simulated. We find that the Reynolds number based on onset velocity and Archimedes number follows a power-law relationship. With the decrease of Archimedes number, the discrepancy of Reynolds number based on onset velocity and that on particle terminal velocity becomes highly significant. The ratio of the onset velocity to particle terminal velocity for various particles in one liquid medium is not a constant, and instead dependent on both the particle and liquid properties.

CFD-DEM Modeling and Simulation Coupled to a Global Thermodynamic Analysis Methodology for Evaluating Energy Performance: Biofertilizer Industry

This work develops a methodology based on real chemical plant data collected from a Nitrogen-Phosphorus-Potassium fertilizer (NPK) cooling rotary drum. By blending thermodynamic variables given by global energy and mass balances with computational fluid dynamics-discrete element method (CFD-DEM) modeling and simulation, the methodology provides an initial approximation to the understanding of heat transfer inside industry rotary coolers. The NPK cooling process was modeled in CFD software Simcenter STAR − CCM + 13.06.011 using a Eulerian–Lagrangian scheme through a coupled CFD-DEM method using one-way coupling. The average temperature of the NPK particles was obtained as well as the average mass flow of the particles dropping as the drum was rotating. The analysis was performed for two-particle diameters (8 and 20 mm) during 17.5 s. The average heat transfer coefficient between the fluid and the NPK particles during the simulated time was obtained. A thermodynamic analysis was carried out using instantaneous energy and mass balances. Prandtl, Nusselt, and Reynolds numbers were obtained for each simulated time step. Finally, through a non-linear regression using the Marquardt method, a correlation between Prandtl, Nusselt, and Reynolds number was developed that allowed analyzing the rotating drum. Results showed that the proposed methodology could serve as a useful tool during the design and analysis of any given rotary cooler, allowing calculation of the heat transfer coefficient and obtaining the process variables that could expand the machine operational capabilities due to the knowledge of the Nusselt number as a function of the drum working parameters.

Development of a methodology for predicting particle attrition in a cyclone by CFD-DEM

Cyclones are commonly used in the process industry to separate entrained particles from gas streams. Particles entering a cyclone are subjected to a centrifugal force field, driving them to the cyclone walls, where they experience collisional and rapid shearing stresses. Consequently, particle attrition and erosion of the cyclone walls occur, depending on the mechanical properties of the particles and cyclone walls.In this work, the attrition of manganese oxide particles, intended for use in the Chemical Looping Combustion (CLC) process, flowing through a standard design cyclone (Stairmand design) is analysed as an example by considering surface damage processes of chipping and wear. A new methodology is developed, whereby Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulations are used to analyse the particle motion and interactions with the cyclone walls. The approach is then coupled with breakage models of chipping and wear to predict the extent of attrition.The impact breakage due to chipping is evaluated experimentally first as a function of particle size and impact angle and velocity. The data are fitted to the chipping model of Ghadiri and Zhang. The model is then coupled with the frequency of collisions and impact velocity, obtained from the CFD-DEM simulation, to work out the particle attrition by chipping. For surface wear the model of Archard is used to account for particle wear by shearing against the walls. The outcome of the work provides a methodology for describing the extent of attrition in different regions of the cyclone.

CFD–DEM simulation of pneumatic conveying in a horizontal channel

In this paper, the pneumatic conveying in a horizontal channel is simulated by the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM). A modified wall roughness model and the Discrete Random Walk (DRW) model are introduced into the CFD–DEM approach to investigate the effect of the wall roughness and the random effect of the turbulence on particle dispersion respectively, and this combined approach is named as the improved CFD–DEM approach. The interaction between the particles and the fluid is calculated by both the one-way coupling method and the two-way coupling method. The accuracy of the improved CFD–DEM approach is validated by corresponding experiments from the literatures. By using the improved CFD–DEM approach, several dense channel gas–solid flows are simulated. The simulation results indicate that with the increase of mass loading rate, the particle agglomeration is more significant, and the trend of increasing the particle concentration near the upper and lower walls is more obvious. This research shows that the improved CFD–DEM approach developed in this work is an effective tool for studying the particle phase properties under both dilute and dense phase conditions.

CFD-DEM simulation of drying of food grains with particle shrinkage

Food grains naturally undergo physical and structural changes during a drying process. The volumetric change of particles or particle shrinkage is one of the important and complicated physical changes in drying. In this work, a shrinkage model for particle diameter reduction is incorporated into the computational fluid dynamics- discrete element method (CFD-DEM) drying model for food grains. First, mixing, general drying and shrinkage characteristics including particle and air moisture content, and particle diameter variation are reproduced. Then, the model is tested by comparing the predicted moisture reduction and volume shrinkage curve with the experimental data of wheat from the literature. The results demonstrate the capability of the current model in predicting drying and particle shrinkage characteristics. Finally, the effects of inlet air temperature and velocity on drying and particle shrinkage are studied. It is revealed that the shrinkage rate increases significantly with increasing air temperature but increases slightly with increasing inlet air velocity. The uniformity of grain size, quantified here by the standard deviation of the particle diameter distribution, increases with decreasing air temperature or increasing air velocity. This grain scale drying model with particle shrinkage should be useful for the design and control of many drying processes.

A Coupled CFD–DEM Simulation of Slurry Infiltration and Filter Cake Formation during Slurry Shield Tunneling

Tunneling in highly permeable ground using a slurry shield machine can be challenging because it is difficult to form the so-called filter cake on the tunnel face to transport the support pressure. Consequently, destructive accidents might happen, such as face instability and water inrush. How to form an efficient filter cake in time is crucial during engineering practice, especially in ground with high permeability. Various theoretical and experimental analyses regarding the formation of filter cakes have been conducted. However, due to the complexity of this problem, which has to incorporate the mechanical and hydraulic behaviors of the fluid–solid mixture system, few numerical simulations are found in the literature. In this paper, with the aid of a newly developed numerical tool, a coupled CFD (computational fluid dynamics)–DEM (discrete element method) simulation is established to study the slurry infiltration and filter cake formation during slurry shield tunneling. The slurry infiltration process is simulated by modelling the scheme of the infiltration column test, in which sedimentation behaviors of slurry particles are captured and compared with experimental results. The results show that the sedimentation behaviors of the slurry particles and filter cake formation phenomenon are well captured by simulations and in accordance with the experiments, which indicates the robustness of the coupled CFD–DEM simulation used in present work.

CFD–DEM simulation of a pseudo-two-dimensional spouted bed comprising coarse particles

In the present study, computational fluid dynamics (CFD) and the discrete element method (DEM) are used in conjunction with the Eulerian–Lagrangian method to simulate a pseudo-two-dimensional spouted bed comprising coarse 6-mm particles. The open-source OpenFOAM code is used to solve the governing equations. The predicted vertical particle velocity along the bed axis, particle velocity profiles in the radial direction, power spectral density, time-averaged particle velocity vectors, bed pressure drop, and solid flow pattern are evaluated and compared with existing experimental data. Good agreement is found between the CFD–DEM results and the measured data. It is also shown that the present CFD–DEM model accurately predicts the particle flow pattern throughout the bed. It is found that the drag force, solid stresses, and gravity play important roles in the CFD–DEM simulation of a spouted bed comprising coarse particles.

Multiscale investigation of tube erosion in fluidized bed based on CFD-DEM simulation

A multiscale analysis on the erosion of the immersed tubes in a 3-D fluidized bed is conducted using computational fluid dynamics–discrete element method (CFD-DEM) coupling a particle-scale erosion model referred to as the shear impact energy model (SIEM). Different gas velocities and tube shapes are adopted to obtain more information. Several hydrodynamic parameters, including the void and solid fraction, the average particle speed, the granular temperature and the fluctuation energy (defined as the sum of the granular temperature) have been obtained and analyzed. Since the hydrodynamic properties have great effect on erosion of the immersed tube, a quantitative analysis was carried out based on the hydrodynamic parameters around the tubes. An intrinsic relation between erosion on the immersed tube and the fluctuation energy has been revealed based on the analysis, which indicates that the fluctuation energy of the particles near the tube probably is the main reason for the erosion. Moreover, the ordered motion of the particles also has some effect on the erosion, especially on the erosion of the top and bottom of the tube when the gas velocity is high.

Investigation of Void Fraction Schemes for Use with CFD-DEM Simulations of Fluidized Beds

This paper investigates the spatial resolution of computational fluid dynamics–discrete element method (CFD-DEM) simulations of a bubbling fluidized bed for seven different void fraction schemes. Fluid grids with cell sizes of 3.5, 1.6, and 1.3 particle diameters were compared. The particle velocity maps from all of the void fraction schemes were in good qualitative agreement with the experimental data collected using magnetic resonance imaging (MRI). Refining the fluid grid improved the quantitative agreement due to a more accurate representation of flow near the gas distributor. The approach proposed by Khawaja et al. [J. Comput. Multiphase Flows 2012, 4, 183−192] provided the closest match to the exact void fraction though only the particle centered method differed significantly. These results indicate that the fluid grid used for CFD-DEM simulations must be sufficiently fine to represent the inlet flow realistically and that a void fraction scheme such as that proposed by Khawaja be used.

Erosion prediction of industrial conveying pipelines

In this paper, a new concept of the one-dimensional erosion model (ODEM) is presented, validated, and implemented for a pneumatic conveying system. The ODEM is a combination of a one-dimensional flow model and statistical distribution functions that describe the particle-wall collision characteristics. Computational fluid dynamics/discrete element method (CFD-DEM) simulations serve as a numerical tool for deriving the statistical functions of the collision characteristics and as a basis for ODEM validation. Both the ODEM and the CFD-DEM are implemented for the same pneumatic conveying system in order to compare their performances. The developed statistical functions for straight pipes and bends include collision frequency, circumference angle, impact angle, and impact velocity magnitude. An additional bend angle function is developed for bends. It is found that most of the parameters can be formulated by a single distribution function that describes all the sections of the system. A distinct feature is discovered, i.e., using a non-dimensional form of the impact velocity function (the ratio of the impact velocity magnitude to the median impact velocity) yields similar statistical distributions for all bends and straight sections in the conveying system. Furthermore, the median impact velocity is correlated with particle axial velocity. Therefore, this non-dimensional form can be used in a wide range of applications for estimating the distribution of the impact velocity of particles in dilute pneumatic conveying. The statistical functions describe each parameter independently, which means that they can be measured or computed regardless of one another, thereby facilitating fast and easy erosion prediction. The erosion rate results of the ODEM and the DEM for the entire conveying system are found to be in excellent agreement (straight sections and bends). This validates the ODEM as a tool for predicting the erosion rate in conveying lines, including bends and straight sections, at a much faster rate than 3D CFD-DEM simulations (the computation time ratio is estimated to be 1/54).