Sedimentation of particles in inclined and vertical vessels is numerically simulated by the Eulerian two-fluid model. The numerical results show an interesting phenomenon with two circulation vortexes in a vertical ve...Sedimentation of particles in inclined and vertical vessels is numerically simulated by the Eulerian two-fluid model. The numerical results show an interesting phenomenon with two circulation vortexes in a vertical vessel but one in the inclined vessel. Sensitivity tests indicate that the boundary layer effect is the key to induce this phenomenon. A numerical method based on 2D unstructured meshes is presented to solve the hard-sphere discrete particle model. Several applications show the numerical method has a good performance to simulate dense particulate flows in irregular domains without regard to element types of the mesh.展开更多
A hydrodynamic model is used to study Kelvin-Helmholtz(KH)instability of the interface between two particle-laden inviscid fluids moving with two different uniform mean velocities.Explicit eigen-equation is derived to...A hydrodynamic model is used to study Kelvin-Helmholtz(KH)instability of the interface between two particle-laden inviscid fluids moving with two different uniform mean velocities.Explicit eigen-equation is derived to study the effect of suspended particles on the growth rate of KH instability.For dusty gases with negligible volume fraction of heavy particles and small particle-to-fluid mass ratio,the real and imaginary parts of leading-order asymptotic expression derived by the present model for the growth rate are shown to be identical to the earlier results derived by the classical Saffman model established for dusty gases.Beyond the known results,explicit leading-order asymptotic expressions for the effect of suspended particles on the growth rate are derived for several typical cases of basic interest.It is shown that the suspended particles can decrease or increase the growth rate of KH instability depending on the Stokes numbers of the particles and whether the particles are heavier or lighter than the clean fluid.Compared to the mass density of the clean fluid,our results based on leading-order asymptotic solutions show that heavier particles and lighter particles have opposite effects on the growth rate of KH instability,while the effect of neutrally buoyant particles on the growth rate of KH instability is negligible.展开更多
The Euler-Euler model is less effective in capturing the free surface of flow film in the spiral separator,and thus a Eulerian multi-fluid volume of fluid(VOF)model was first proposed to describe the particulate flow ...The Euler-Euler model is less effective in capturing the free surface of flow film in the spiral separator,and thus a Eulerian multi-fluid volume of fluid(VOF)model was first proposed to describe the particulate flow in spiral separators.In order to improve the applicability of the model in the high solid concentration system,the Bagnold effect was incorporated into the modelling framework.The capability of the proposed model in terms of predicting the flow film shape in a LD9 spiral separator was evaluated via comparison with measured flow film thicknesses reported in literature.Results showed that sharp air–water and air-pulp interfaces can be obtained using the proposed model,and the shapes of the predicted flow films before and after particle addition were reasonably consistent with the observations reported in literature.Furthermore,the experimental and numerical simulation of the separation of quartz and hematite were performed in a laboratory-scale spiral separator.When the Bagnold lift force model was considered,predictions of the grade of iron and solid concentration by mass for different trough lengths were more consistent with experimental data.In the initial development stage,the quartz particles at the bottom of the flow layer were more possible to be lifted due to the Bagnold force.Thus,a better predicted vertical stratification between quartz and hematite particles was obtained,which provided favorable conditions for subsequent radial segregation.展开更多
Hydroabrasion in particulate flows plays an important role in various industrial and natural processes. To predict the effects of particulate flow and the resulting phenomena such as erosion/abrasion in a pipeline, ch...Hydroabrasion in particulate flows plays an important role in various industrial and natural processes. To predict the effects of particulate flow and the resulting phenomena such as erosion/abrasion in a pipeline, channel or a fitting, it is essential to characterize the effects in a simple standardized geometry. For this purpose, it is vital to initially understand the particulate flow behavior and motion in such geometries. In the present work, two series of experimental works by application of the LDA measurement technique were successfully conducted. First, the particulate flow behavior at downstream of a flow conditioner inside a channel with square cross-section was investigated. Shorter lengths for fully development of velocity profile by using the self-constructed flow conditioner were observed. Moreover, the flow at downstream of the conditioner was modeled with the CFD tool (ANSYS-CFX V. 14.57) and the simulation results were compared and validated by the LDA experimental data. Better agreement between the simulation results and experimental data was observed in the fully developed region. However, there are some deviations due to the actual pressure loss through the experimental loop and the calculated pressure loss value, which includes some assumptions for the loss coefficients. Furthermore, the particulate flow behavior and vortex generation inside the deformed locations of a channel surface were studied in detail. With the help of the Matlab program, it was possible to calculate and visualize the velocity vectors for each measured point inside the channel accurately.展开更多
We present the simulation of the dynamics of fluid-cylinder interactions in a narrow three-dimensional channel filled with a Newtonian fluid, using a Lagrange multiplier based fictitious domain methodology combined wi...We present the simulation of the dynamics of fluid-cylinder interactions in a narrow three-dimensional channel filled with a Newtonian fluid, using a Lagrange multiplier based fictitious domain methodology combined with a finite element method and an operator splitting technique. As expected, a settling truncated cylinder turns its broadside perpendicular to the main stream direction and the center of mass moves to the central axis of the channel. In the case of two truncated cylinders, they first move around each other for a while and then stay together in a "T" shape. After the "T" shape has been formed for a long enough time, we found no vortex shedding behind the cylinders. When simulating the fluidization of 60 truncated cylinders, we captured the features of interactions among fluidized cylinders as observed in experiments.展开更多
Lattice Boltzmann method was used to numerically investigate the motion and orientation distribution of cylindrical and cubic particles in pipe flow with high concentration and high particle to pipe size ratio. The tr...Lattice Boltzmann method was used to numerically investigate the motion and orientation distribution of cylindrical and cubic particles in pipe flow with high concentration and high particle to pipe size ratio. The transient impulse model of 3D collisions between particles and between particle and wall is proposed. The numerical results are qualitatively in agreement with and quantitatively comparable to the experiment data. The results show that the increases of both the cylindrical particle to pipe size ratio and the particle aspect ratio decrease the rotation about all axes. All rotations of cubic particles decrease with increasing the particle concentration. The cubic particles, rotating more drastically in the flow with large Reynolds number, rotate faster than the cylindrical particles with the same size. The cylindrical particles align with the flow direction more obviously with decreasing Reynolds numbers. However, the orientations of cubic particles are spread all over the range with no significant difference in magnitude, and the Reynolds numbers have no obvious effect on the orientations of cubic particles.展开更多
The stability and mobility of proppant packs in hydraulic fractures during hydrocarbon production are numerically investigated by the lattice Boltzmann-discrete element coupling method(LB-DEM).This study starts with a...The stability and mobility of proppant packs in hydraulic fractures during hydrocarbon production are numerically investigated by the lattice Boltzmann-discrete element coupling method(LB-DEM).This study starts with a preliminary proppant settling test,from which a solid volume fraction of 0.575 is calibrated for the proppant pack in the fracture.In the established workflow to investigate proppant flowback,a displacement is applied to the fracture surfaces to compact the generated proppant pack as well as further mimicking proppant embedment under closure stress.When a pressure gradient is applied to drive the fluid-particle flow,a critical aperture-to-diameter ratio of 4 is observed,above which the proppant pack would collapse.The results also show that the volumetric proppant flowback rate increases quadratically with the fracture aperture,while a linear variation between the particle flux and the pressure gradient is exhibited for a fixed fracture aperture.The research outcome contributes towards an improved understanding of proppant flowback in hydraulic fractures,which also supports an optimised proppant size selection for hydraulic fracturing operations.展开更多
An improved implementation of distributed multiplier/fictitious domain method is presented for the direct numerical simulation of particulate flow. The key improvement is to replace a finite element triangulation for...An improved implementation of distributed multiplier/fictitious domain method is presented for the direct numerical simulation of particulate flow. The key improvement is to replace a finite element triangulation for the velocity and a “twice coarser' triangulation for the pressure with a rectangular discretization for the velocity and pressure. For code validation, the sedimentation of a single particle in a two dimensional channel was simulated. The results showed that the simulation is independent of the mesh size as well as the time step. The comparison between experimental data and this simulation showed that our code can give a more accurate simulation on the motion of particles than previous DLM code. The code was then applied to simulate the sedimentation of 600 particles in a rectangular box. The falling course is presented and discussed. At the same time, this simulation also demonstrates that the method presented in this paper can be used for solving the initial problems involving a lager number of particles exactly with computing durations kept at acceptable levels.展开更多
In this paper,the mechanisms of material removal in chemical mechanical polishing(CMP)processes are investigated in detail by the smoothed particle hydrodynamics(SPH)method.The feature-scale behaviours of slurry flow,...In this paper,the mechanisms of material removal in chemical mechanical polishing(CMP)processes are investigated in detail by the smoothed particle hydrodynamics(SPH)method.The feature-scale behaviours of slurry flow,rough pad,wafer defects,moving solid boundaries,slurry-abrasive interactions,and abrasive collisions are modelled and simulated.Compared with previous work on CMP simulations,our simulations incorporate more realistic physical aspects of the CMP process,especially the effect of abrasive concentration in the slurry flows.The preliminary results on slurry flow in CMP provide microscopic insights on the experimental data of the relation between the removal rate and abrasive concentration and demonstrate that SPH is a suitable method for the research of CMP processes.展开更多
In order to study the effect of heat flux and inlet temperature on the fouling characteristics of nanoparticles, and to further reveal the fouling mechanism for insights into proper operating conditions, γ-Al_2O_3/wa...In order to study the effect of heat flux and inlet temperature on the fouling characteristics of nanoparticles, and to further reveal the fouling mechanism for insights into proper operating conditions, γ-Al_2O_3/water suspensions were chosen as the subject of this research. The particulate fouling characteristics of γ-Al_2O_3/water suspensions on the surface of stainless steel have been experimentally studied by varying the heat flux and the inlet temperature under single-phase flow and subcooled-flow boiling conditions. The results show that in the condition of single-phase flow, the asymptotic value of fouling resistance decreases with increasing of heat flux and inlet temperature. The asymptotic value of fouling resistance under single-phase flow is much higher than for the subcooled-flow boiling condition. The effect of heat flux on the fouling resistance under the two flow states has an inverse relationship, and there exists a minimum value of fouling resistance between these two states. For subcooled-flow boiling, the asymptotic value of fouling resistance increases with increasing heat flux, whereas the effect on fouling resistance by the inlet temperature is negligible.展开更多
A parallelized resolved method for the simulation of the dynamics of immersed bodies within fluids is presented. The algorithm uses a FDM （fictitious domain method） and combines the Lagrangian DEM （discrete element...A parallelized resolved method for the simulation of the dynamics of immersed bodies within fluids is presented. The algorithm uses a FDM （fictitious domain method） and combines the Lagrangian DEM （discrete element method） for tracking the bodies with a CFD （computational fluid dynamics） method for calculating the dynamics of the fluid phase. First the CFD-calculation is carried out, disregarding the solid bodies. Afterwards, the velocity information from the bodies is included and the force, the fluid imposes onto the bodies, is computed. The last step consists of a correction-operation which ensures the fulfillment of the conservation equation. Dynamic local mesh refinement is used for minimizing the number of fluid cells. The CFD-DEM coupling is realized within the Open Source framework CFDEMcoupling （www.cfdem.com）, where the DEM software LIGGGHTS （www.liggghts.com） is linked against an OpenFOAM^-based CFD solver. While both LIGGGHTS and the CFD solver were already parallelized, only a recent improvement of the algorithm permits the fully parallel computation of resolved problems. This parallelization permits the treatment of large-scale problems. The enclosed validation and application examples show the dynamics of the flow around settling and rotating spheres as well as an investigation of the settling of spheres regarding the Boycott effect.展开更多
The accurate simulation of disperse two-phase flows,where a discrete particulate condensed phase is transported by a carrier gas,is crucial for many applications;Eulerian approaches are well suited for high performanc...The accurate simulation of disperse two-phase flows,where a discrete particulate condensed phase is transported by a carrier gas,is crucial for many applications;Eulerian approaches are well suited for high performance computations of such flows.However when the particles from the disperse phase have a significant inertia compared to the time scales of the flow,particle trajectory crossing(PTC)occurs i.e.the particle velocity distribution at a given location can become multi-valued.To properly account for such a phenomenon many Eulerian moment methods have been recently proposed in the literature.The resulting models hardly comply with a full set of desired criteria involving:1-ability to reproduce the physics of PTC,at least for a given range of particle inertia,2-well-posedness of the resulting set of PDEs on the chosen moments as well as guaranteed realizability,3-capability of the model to be associated with a high order realizable numerical scheme for the accurate resolution of particle segregation in turbulent flows.The purpose of the present contribution is to introduce a multi-variate Anisotropic Gaussian closure for such particulate flows,in the spirit of the closure that has been suggested for out-of-equilibrium gas dynamics and which satisfies the three criteria.The novelty of the contribution is three-fold.First we derive the related moment system of conservation laws with source terms,and justify the use of such a model in the context of high Knudsen numbers,where collision operators play no role.We exhibit the main features and advantages in terms of mathematical structure and realizability.Then a second order accurate and realizable MUSCL/HLL scheme is proposed and validated.Finally the behavior of the method for the description of PTC is thoroughly investigated and its ability to account accurately for inertial particulate flow dynamics in typical configurations is assessed.展开更多
A fluid-structure interaction method based on the arbitrary Lagrangian-Eulerian method and a dynamic mesh method was developed to simulate the dynamics of a rigid particle in shear flows.In the method,the governing eq...A fluid-structure interaction method based on the arbitrary Lagrangian-Eulerian method and a dynamic mesh method was developed to simulate the dynamics of a rigid particle in shear flows.In the method,the governing equations for the fluid flow and particle motion were sequentially solved in a two-way coupling fashion.The mesh system was deformed or re-meshed by the dynamic mesh method.The method was employed to simulate the dynamics of a single particle suspended in a flow channel and the dynamics of the particle were studied.The simulation results show that the angular velocity is not only a function of the inclination angle,is but also influenced by the aspect ratio yielding a hysteresis,while the angular velocity obtained from the Keller-Scalak model is a function only of the inclination angle and does not show a hysteresis.The present simulations clearly demonstrate that the Fluid-Structure Interaction（FSI） module is very stable,accurate and robust.展开更多
A boundary condition-enforced immersed boundary-lattice Boltzmannmethod (IB-LBM) for the simulation of particulate flows is presented in this paper. Ingeneral, the immersed boundary method (IBM) utilizes a discrete se...A boundary condition-enforced immersed boundary-lattice Boltzmannmethod (IB-LBM) for the simulation of particulate flows is presented in this paper. Ingeneral, the immersed boundary method (IBM) utilizes a discrete set of force densityto represent the effect of boundary. In the conventional IB-LBM, such force density ispre-determined, which cannot guarantee exact satisfaction of non-slip boundary condition. In this study, the force density is transferred to the unknown velocity correctionwhich is determined by enforcing the non-slip boundary condition. For the particulateflows, accurate calculation of hydrodynamic force exerted on the boundary of particlesis of great importance as it controls the motion of particles. The capability of presentmethod for particulate flows is depicted by simulating migration of one particle in asimple shear flow and sedimentation of one particle in a box and two particles in achannel. The expected phenomena and numerical results are achieved. In addition,particle suspension in a 2D symmetric stenotic artery is also simulated.展开更多
In this article,we employ a fully-resolved numerical simulation method（the fictitious domain method）to investigate the effects of large neutrally-buoyant particles on the turbulent flow in a pipe at low Reynolds num...In this article,we employ a fully-resolved numerical simulation method（the fictitious domain method）to investigate the effects of large neutrally-buoyant particles on the turbulent flow in a pipe at low Reynolds number and non-dilute regimes.The tube Reynolds number is fixed to be 4 900,the particle-pipe diameter ratio is 0.1,and the particle volume fraction ranges from 0.33%to 10%.Our results indicate that the presence of large particles decreases the maximum root-of-mean-square（rms）of the streamwise velocity fluctuation near the wall by weakening the intensity of large-scale streamwise vortices,although in the region very close to the wall the particles increase the rms of streamwise velocity fluctuation.On the other hand,the particles induce small-scale vortices in the near-wall region,resulting in the enhancement of the rms of radial and circumferential velocity fluctuations there.展开更多
Modeling and direct numerical simulation of particle-laden flows have a tremendous variety of applications in science and engineering across a vast spectrum of scales from pollution dispersion in the atmosphere,to flu...Modeling and direct numerical simulation of particle-laden flows have a tremendous variety of applications in science and engineering across a vast spectrum of scales from pollution dispersion in the atmosphere,to fluidization in the combustion process,to aerosol deposition in spray medication,along with many others.Due to their strongly nonlinear and multiscale nature,the above complex phenomena still raise a very steep challenge to themost computationalmethods.In this review,we provide comprehensive coverage of multibody hydrodynamic(MBH)problems focusing on particulate suspensions in complex fluidic systems that have been simulated using hybrid Eulerian-Lagrangian particulate flow models.Among these hybridmodels,the Immersed Boundary-Lattice Boltzmann Method(IB-LBM)provides mathematically simple and computationally-efficient algorithms for solid-fluid hydrodynamic interactions in MBH simulations.This paper elaborates on the mathematical framework,applicability,and limitations of various’simple to complex’representations of closecontact interparticle interactions and collision methods,including short-range interparticle and particle-wall steric interactions,spring and lubrication forces,normal and oblique collisions,and mesoscale molecular models for deformable particle collisions based on hard-sphere and soft-sphere models in MBH models to simulate settling or flow of nonuniform particles of different geometric shapes and sizes in diverse fluidic systems.展开更多
An algorithm using the discrete element method(DEM)for simulating the particulate behaviour of flow and heat transfer is developed and described,the reasonable hypothesis and the ingenious design of which have been pr...An algorithm using the discrete element method(DEM)for simulating the particulate behaviour of flow and heat transfer is developed and described,the reasonable hypothesis and the ingenious design of which have been presented in detail.The organizational structure of the developed algorithm contains an efficient method for determining particle collisions,the status analysis for each particle and the particulate-kinematics analysis during the time step.The reasonability and correctness of the developed DEM algorithm are validated by laboratory experiments:the discharge process of glass beads from a silo;and heating of metal alloy particles in a calciner.Afterwards,a group of validated mechanics parameter values for coal and sand have been tested and verified in the article,preparing for the simulation of the pyrolysis process in a downer or screw reactor in subsequent research projects.展开更多
A novel triaxial vibration method is developed for the real-time characterization of the solid particle size distribution(PsD)in pneumatic particulate flow,which is critical for chemical industry.In this work,the part...A novel triaxial vibration method is developed for the real-time characterization of the solid particle size distribution(PsD)in pneumatic particulate flow,which is critical for chemical industry.In this work,the particle-wall collision and friction behaviours were analysed by the time-domain statistical and timefrequency joint methods to narrow the high-frequency response range by the initial experiment of free fall for a single particle,interparticle,and multiple particles.Subsequently,verification experiments of PSD characterization in pneumatic flow were performed.First,the quantitative triaxial energy response model that considers the particle size,shape,and mass factors were established.Second,a good agreement of the particle number identification was found between the triaxial vibration energy and mean particle size of 150-550μm.Moreover,the performance with the best accuracy was focused on a range of 42-43 kHz in the x-axis and z-axis and 36.8-38.8 kHz in the y-axis.Finally,the individual particle energy was inversely analysed by the triaxial vibration response within the optimized frequency bands,and the PSD was characterized in real-time by a low error rate,that is,5.2% from the XZ-axis direction of sand(42-43 kHz)and 5.6% from the XYZ-axis of glass(30.9-33.9 kHz,46.2-47.2 kHz,38.3-41.3 kHz for each axis response).Therefore,this research complements the existing approaches for PsD characterization in particulate multiphase flow.展开更多
Particle transport phenomena in small-scale circulating fiuidized beds （CFB） can be simulated using the Euler-Euler, discrete element method, and Euler-Lagrange approaches. In this work, a hybrid Euler-Lagrange mode...Particle transport phenomena in small-scale circulating fiuidized beds （CFB） can be simulated using the Euler-Euler, discrete element method, and Euler-Lagrange approaches. In this work, a hybrid Euler-Lagrange model known as the dense discrete phase model （DDPM）, which has common roots with the multiphase particle-in-cell model, was applied in simulating particle transport within a mid-sized experimental CFB facility. Implementation of the DDPM into the commercial ANSYS Fluent CFD package is relatively young in comparison with the granular Eulerian model. For that reason, validation of the DDPM approach against experimental data is still required and is addressed in this paper. Additional difficulties encountered in modeling fluidization processes are connected with long calculation times. To reduce times, the complete boiler models are simplified to include just the combustion chamber. Such simplifications introduce errors in the predicted solid distribution in the boiler. To investigate the conse- quences of model reduction, simulations were made using the simplified and complete pilot geometries and compared with experimental data. All simulations were performed using the ANSYSFLUENT 14.0 package. A set of user defined functions were used in the hybrid DDPM and Euler-Euler approaches to recirculate solid particles.展开更多
The lattice Boltzmann method （LBM） is a useful technique for simulating multiphase flows and modeling complex physics. Specifically, we use LBM combined with a direct-forcing （DF） immersed boundary （IB） method t...The lattice Boltzmann method （LBM） is a useful technique for simulating multiphase flows and modeling complex physics. Specifically, we use LBM combined with a direct-forcing （DF） immersed boundary （IB） method to simulate fluid-particle interactions in two-phase particulate flows. Two grids are used in the simulation： a fixed uniform Eulerian grid for the fluid phase and a Lagrangian grid that is attached to and moves with the immersed particles. Forces are calculated at each Lagrangian point. To exchange numerical information between the two grids, discrete delta functions are used. The resulting DF IB-LBM approach is then successfully applied to a variety of reference flows, namely the sedimentation of one and two circular particles in a vertical channel, the sedimentation of one or two spheres in an enclosure, and a neutrally buoyant prolate spheroid in a Couette flow. This last application proves that the developed approach can be used also for non-spherical particles. The three forcing schemes and the different factors affecting the simulation （added mass effect, corrected radius） are also discussed.展开更多
文摘Sedimentation of particles in inclined and vertical vessels is numerically simulated by the Eulerian two-fluid model. The numerical results show an interesting phenomenon with two circulation vortexes in a vertical vessel but one in the inclined vessel. Sensitivity tests indicate that the boundary layer effect is the key to induce this phenomenon. A numerical method based on 2D unstructured meshes is presented to solve the hard-sphere discrete particle model. Several applications show the numerical method has a good performance to simulate dense particulate flows in irregular domains without regard to element types of the mesh.
文摘A hydrodynamic model is used to study Kelvin-Helmholtz(KH)instability of the interface between two particle-laden inviscid fluids moving with two different uniform mean velocities.Explicit eigen-equation is derived to study the effect of suspended particles on the growth rate of KH instability.For dusty gases with negligible volume fraction of heavy particles and small particle-to-fluid mass ratio,the real and imaginary parts of leading-order asymptotic expression derived by the present model for the growth rate are shown to be identical to the earlier results derived by the classical Saffman model established for dusty gases.Beyond the known results,explicit leading-order asymptotic expressions for the effect of suspended particles on the growth rate are derived for several typical cases of basic interest.It is shown that the suspended particles can decrease or increase the growth rate of KH instability depending on the Stokes numbers of the particles and whether the particles are heavier or lighter than the clean fluid.Compared to the mass density of the clean fluid,our results based on leading-order asymptotic solutions show that heavier particles and lighter particles have opposite effects on the growth rate of KH instability,while the effect of neutrally buoyant particles on the growth rate of KH instability is negligible.
基金the National Natural Science Foundation of China(Nos.51974065 and 52274257)the Open Foundation of State Key Laboratory of Mineral Processing(No.BGRIMMKJSKL-2020-13)the Fundamental Research Funds for the Central Universities(Nos.N2201008 and N2201004).
文摘The Euler-Euler model is less effective in capturing the free surface of flow film in the spiral separator,and thus a Eulerian multi-fluid volume of fluid(VOF)model was first proposed to describe the particulate flow in spiral separators.In order to improve the applicability of the model in the high solid concentration system,the Bagnold effect was incorporated into the modelling framework.The capability of the proposed model in terms of predicting the flow film shape in a LD9 spiral separator was evaluated via comparison with measured flow film thicknesses reported in literature.Results showed that sharp air–water and air-pulp interfaces can be obtained using the proposed model,and the shapes of the predicted flow films before and after particle addition were reasonably consistent with the observations reported in literature.Furthermore,the experimental and numerical simulation of the separation of quartz and hematite were performed in a laboratory-scale spiral separator.When the Bagnold lift force model was considered,predictions of the grade of iron and solid concentration by mass for different trough lengths were more consistent with experimental data.In the initial development stage,the quartz particles at the bottom of the flow layer were more possible to be lifted due to the Bagnold force.Thus,a better predicted vertical stratification between quartz and hematite particles was obtained,which provided favorable conditions for subsequent radial segregation.
文摘Hydroabrasion in particulate flows plays an important role in various industrial and natural processes. To predict the effects of particulate flow and the resulting phenomena such as erosion/abrasion in a pipeline, channel or a fitting, it is essential to characterize the effects in a simple standardized geometry. For this purpose, it is vital to initially understand the particulate flow behavior and motion in such geometries. In the present work, two series of experimental works by application of the LDA measurement technique were successfully conducted. First, the particulate flow behavior at downstream of a flow conditioner inside a channel with square cross-section was investigated. Shorter lengths for fully development of velocity profile by using the self-constructed flow conditioner were observed. Moreover, the flow at downstream of the conditioner was modeled with the CFD tool (ANSYS-CFX V. 14.57) and the simulation results were compared and validated by the LDA experimental data. Better agreement between the simulation results and experimental data was observed in the fully developed region. However, there are some deviations due to the actual pressure loss through the experimental loop and the calculated pressure loss value, which includes some assumptions for the loss coefficients. Furthermore, the particulate flow behavior and vortex generation inside the deformed locations of a channel surface were studied in detail. With the help of the Matlab program, it was possible to calculate and visualize the velocity vectors for each measured point inside the channel accurately.
文摘We present the simulation of the dynamics of fluid-cylinder interactions in a narrow three-dimensional channel filled with a Newtonian fluid, using a Lagrange multiplier based fictitious domain methodology combined with a finite element method and an operator splitting technique. As expected, a settling truncated cylinder turns its broadside perpendicular to the main stream direction and the center of mass moves to the central axis of the channel. In the case of two truncated cylinders, they first move around each other for a while and then stay together in a "T" shape. After the "T" shape has been formed for a long enough time, we found no vortex shedding behind the cylinders. When simulating the fluidization of 60 truncated cylinders, we captured the features of interactions among fluidized cylinders as observed in experiments.
基金Project (No. 10632070) supported by the National Natural Science Foundation of China
文摘Lattice Boltzmann method was used to numerically investigate the motion and orientation distribution of cylindrical and cubic particles in pipe flow with high concentration and high particle to pipe size ratio. The transient impulse model of 3D collisions between particles and between particle and wall is proposed. The numerical results are qualitatively in agreement with and quantitatively comparable to the experiment data. The results show that the increases of both the cylindrical particle to pipe size ratio and the particle aspect ratio decrease the rotation about all axes. All rotations of cubic particles decrease with increasing the particle concentration. The cubic particles, rotating more drastically in the flow with large Reynolds number, rotate faster than the cylindrical particles with the same size. The cylindrical particles align with the flow direction more obviously with decreasing Reynolds numbers. However, the orientations of cubic particles are spread all over the range with no significant difference in magnitude, and the Reynolds numbers have no obvious effect on the orientations of cubic particles.
基金Funding support from Heilongjiang"Open Competition"project(Grant No.DQYT2022-JS-758)is greatly acknowledgedFinancial support from the National Natural Science Foundation of China(Grant Nos.52304025 and 52174025)is acknowledged+1 种基金supports from Northeast Petroleum University and Guangdong Basic and Applied Basic Research Foundationsupport from the Heilongjiang Touyan Innovation Team Program.
文摘The stability and mobility of proppant packs in hydraulic fractures during hydrocarbon production are numerically investigated by the lattice Boltzmann-discrete element coupling method(LB-DEM).This study starts with a preliminary proppant settling test,from which a solid volume fraction of 0.575 is calibrated for the proppant pack in the fracture.In the established workflow to investigate proppant flowback,a displacement is applied to the fracture surfaces to compact the generated proppant pack as well as further mimicking proppant embedment under closure stress.When a pressure gradient is applied to drive the fluid-particle flow,a critical aperture-to-diameter ratio of 4 is observed,above which the proppant pack would collapse.The results also show that the volumetric proppant flowback rate increases quadratically with the fracture aperture,while a linear variation between the particle flux and the pressure gradient is exhibited for a fixed fracture aperture.The research outcome contributes towards an improved understanding of proppant flowback in hydraulic fractures,which also supports an optimised proppant size selection for hydraulic fracturing operations.
基金TheNationalNaturalSciencesFoundationforOutstandingYouthofChina (No .19925210)andZhejiangProvincialNaturalScienceFoundationofChina(No .10 10 4 7)
文摘An improved implementation of distributed multiplier/fictitious domain method is presented for the direct numerical simulation of particulate flow. The key improvement is to replace a finite element triangulation for the velocity and a “twice coarser' triangulation for the pressure with a rectangular discretization for the velocity and pressure. For code validation, the sedimentation of a single particle in a two dimensional channel was simulated. The results showed that the simulation is independent of the mesh size as well as the time step. The comparison between experimental data and this simulation showed that our code can give a more accurate simulation on the motion of particles than previous DLM code. The code was then applied to simulate the sedimentation of 600 particles in a rectangular box. The falling course is presented and discussed. At the same time, this simulation also demonstrates that the method presented in this paper can be used for solving the initial problems involving a lager number of particles exactly with computing durations kept at acceptable levels.
基金D.W.,C.Y.and X.Z.were partially supported by National Natural Science Foundation of China(Nos.61125401,61376040,61228401,61274032)the National Basic Research Program of China(No.2011CB309701)+8 种基金the National Major Science and Technology Special Project of China(Nos.2011ZX01035-001-001-003,2014ZX02301002-002)Shanghai Science and Technology Committee project(No.13XD1401100)the State Key Laboratory of ASIC and System(Fudan University)research project(No.11MS013).S.S.was partially supported by the National Natural Science Foundation of China(Nos.11101011,91330110)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20110001120112)the State Key Laboratory of ASIC and System(Fudan University)open research project(No.10KF015)W.C.was partially supported by the US Army Office of Research(No.W911NF-11-1-0364)the National Science Foundation of USA(No.DMS-1315128)the National Natural Science Foundation of China(No.91330110).
文摘In this paper,the mechanisms of material removal in chemical mechanical polishing(CMP)processes are investigated in detail by the smoothed particle hydrodynamics(SPH)method.The feature-scale behaviours of slurry flow,rough pad,wafer defects,moving solid boundaries,slurry-abrasive interactions,and abrasive collisions are modelled and simulated.Compared with previous work on CMP simulations,our simulations incorporate more realistic physical aspects of the CMP process,especially the effect of abrasive concentration in the slurry flows.The preliminary results on slurry flow in CMP provide microscopic insights on the experimental data of the relation between the removal rate and abrasive concentration and demonstrate that SPH is a suitable method for the research of CMP processes.
基金Supported by the National Natural Science Foundation of China(51476025)
文摘In order to study the effect of heat flux and inlet temperature on the fouling characteristics of nanoparticles, and to further reveal the fouling mechanism for insights into proper operating conditions, γ-Al_2O_3/water suspensions were chosen as the subject of this research. The particulate fouling characteristics of γ-Al_2O_3/water suspensions on the surface of stainless steel have been experimentally studied by varying the heat flux and the inlet temperature under single-phase flow and subcooled-flow boiling conditions. The results show that in the condition of single-phase flow, the asymptotic value of fouling resistance decreases with increasing of heat flux and inlet temperature. The asymptotic value of fouling resistance under single-phase flow is much higher than for the subcooled-flow boiling condition. The effect of heat flux on the fouling resistance under the two flow states has an inverse relationship, and there exists a minimum value of fouling resistance between these two states. For subcooled-flow boiling, the asymptotic value of fouling resistance increases with increasing heat flux, whereas the effect on fouling resistance by the inlet temperature is negligible.
文摘A parallelized resolved method for the simulation of the dynamics of immersed bodies within fluids is presented. The algorithm uses a FDM （fictitious domain method） and combines the Lagrangian DEM （discrete element method） for tracking the bodies with a CFD （computational fluid dynamics） method for calculating the dynamics of the fluid phase. First the CFD-calculation is carried out, disregarding the solid bodies. Afterwards, the velocity information from the bodies is included and the force, the fluid imposes onto the bodies, is computed. The last step consists of a correction-operation which ensures the fulfillment of the conservation equation. Dynamic local mesh refinement is used for minimizing the number of fluid cells. The CFD-DEM coupling is realized within the Open Source framework CFDEMcoupling （www.cfdem.com）, where the DEM software LIGGGHTS （www.liggghts.com） is linked against an OpenFOAM^-based CFD solver. While both LIGGGHTS and the CFD solver were already parallelized, only a recent improvement of the algorithm permits the fully parallel computation of resolved problems. This parallelization permits the treatment of large-scale problems. The enclosed validation and application examples show the dynamics of the flow around settling and rotating spheres as well as an investigation of the settling of spheres regarding the Boycott effect.
文摘The accurate simulation of disperse two-phase flows,where a discrete particulate condensed phase is transported by a carrier gas,is crucial for many applications;Eulerian approaches are well suited for high performance computations of such flows.However when the particles from the disperse phase have a significant inertia compared to the time scales of the flow,particle trajectory crossing(PTC)occurs i.e.the particle velocity distribution at a given location can become multi-valued.To properly account for such a phenomenon many Eulerian moment methods have been recently proposed in the literature.The resulting models hardly comply with a full set of desired criteria involving:1-ability to reproduce the physics of PTC,at least for a given range of particle inertia,2-well-posedness of the resulting set of PDEs on the chosen moments as well as guaranteed realizability,3-capability of the model to be associated with a high order realizable numerical scheme for the accurate resolution of particle segregation in turbulent flows.The purpose of the present contribution is to introduce a multi-variate Anisotropic Gaussian closure for such particulate flows,in the spirit of the closure that has been suggested for out-of-equilibrium gas dynamics and which satisfies the three criteria.The novelty of the contribution is three-fold.First we derive the related moment system of conservation laws with source terms,and justify the use of such a model in the context of high Knudsen numbers,where collision operators play no role.We exhibit the main features and advantages in terms of mathematical structure and realizability.Then a second order accurate and realizable MUSCL/HLL scheme is proposed and validated.Finally the behavior of the method for the description of PTC is thoroughly investigated and its ability to account accurately for inertial particulate flow dynamics in typical configurations is assessed.
文摘A fluid-structure interaction method based on the arbitrary Lagrangian-Eulerian method and a dynamic mesh method was developed to simulate the dynamics of a rigid particle in shear flows.In the method,the governing equations for the fluid flow and particle motion were sequentially solved in a two-way coupling fashion.The mesh system was deformed or re-meshed by the dynamic mesh method.The method was employed to simulate the dynamics of a single particle suspended in a flow channel and the dynamics of the particle were studied.The simulation results show that the angular velocity is not only a function of the inclination angle,is but also influenced by the aspect ratio yielding a hysteresis,while the angular velocity obtained from the Keller-Scalak model is a function only of the inclination angle and does not show a hysteresis.The present simulations clearly demonstrate that the Fluid-Structure Interaction（FSI） module is very stable,accurate and robust.
文摘A boundary condition-enforced immersed boundary-lattice Boltzmannmethod (IB-LBM) for the simulation of particulate flows is presented in this paper. Ingeneral, the immersed boundary method (IBM) utilizes a discrete set of force densityto represent the effect of boundary. In the conventional IB-LBM, such force density ispre-determined, which cannot guarantee exact satisfaction of non-slip boundary condition. In this study, the force density is transferred to the unknown velocity correctionwhich is determined by enforcing the non-slip boundary condition. For the particulateflows, accurate calculation of hydrodynamic force exerted on the boundary of particlesis of great importance as it controls the motion of particles. The capability of presentmethod for particulate flows is depicted by simulating migration of one particle in asimple shear flow and sedimentation of one particle in a box and two particles in achannel. The expected phenomena and numerical results are achieved. In addition,particle suspension in a 2D symmetric stenotic artery is also simulated.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11072217, 10872181)the Fundamental Research Funds for the Central Universities (Grant Nos. 2009QNA4036, 2010QNA4015)
文摘In this article,we employ a fully-resolved numerical simulation method（the fictitious domain method）to investigate the effects of large neutrally-buoyant particles on the turbulent flow in a pipe at low Reynolds number and non-dilute regimes.The tube Reynolds number is fixed to be 4 900,the particle-pipe diameter ratio is 0.1,and the particle volume fraction ranges from 0.33%to 10%.Our results indicate that the presence of large particles decreases the maximum root-of-mean-square（rms）of the streamwise velocity fluctuation near the wall by weakening the intensity of large-scale streamwise vortices,although in the region very close to the wall the particles increase the rms of streamwise velocity fluctuation.On the other hand,the particles induce small-scale vortices in the near-wall region,resulting in the enhancement of the rms of radial and circumferential velocity fluctuations there.
基金the support of PRIN projects CUP E82F16003010006(principal investigator,G.F.for the Tor Vergata Research Unit)CUP E84I19001020006(principal investigator,G.Bella)financial support fromthe European Research Council under the Horizon 2020 Programme advanced grant agreement no.739964('COPMAT).
文摘Modeling and direct numerical simulation of particle-laden flows have a tremendous variety of applications in science and engineering across a vast spectrum of scales from pollution dispersion in the atmosphere,to fluidization in the combustion process,to aerosol deposition in spray medication,along with many others.Due to their strongly nonlinear and multiscale nature,the above complex phenomena still raise a very steep challenge to themost computationalmethods.In this review,we provide comprehensive coverage of multibody hydrodynamic(MBH)problems focusing on particulate suspensions in complex fluidic systems that have been simulated using hybrid Eulerian-Lagrangian particulate flow models.Among these hybridmodels,the Immersed Boundary-Lattice Boltzmann Method(IB-LBM)provides mathematically simple and computationally-efficient algorithms for solid-fluid hydrodynamic interactions in MBH simulations.This paper elaborates on the mathematical framework,applicability,and limitations of various’simple to complex’representations of closecontact interparticle interactions and collision methods,including short-range interparticle and particle-wall steric interactions,spring and lubrication forces,normal and oblique collisions,and mesoscale molecular models for deformable particle collisions based on hard-sphere and soft-sphere models in MBH models to simulate settling or flow of nonuniform particles of different geometric shapes and sizes in diverse fluidic systems.
文摘An algorithm using the discrete element method(DEM)for simulating the particulate behaviour of flow and heat transfer is developed and described,the reasonable hypothesis and the ingenious design of which have been presented in detail.The organizational structure of the developed algorithm contains an efficient method for determining particle collisions,the status analysis for each particle and the particulate-kinematics analysis during the time step.The reasonability and correctness of the developed DEM algorithm are validated by laboratory experiments:the discharge process of glass beads from a silo;and heating of metal alloy particles in a calciner.Afterwards,a group of validated mechanics parameter values for coal and sand have been tested and verified in the article,preparing for the simulation of the pyrolysis process in a downer or screw reactor in subsequent research projects.
基金supported by Shandong Provincial Natural Science Foundation(grant No.ZR2021ME001)the National Natural Science Foundation of China(grant No.52104015).
文摘A novel triaxial vibration method is developed for the real-time characterization of the solid particle size distribution(PsD)in pneumatic particulate flow,which is critical for chemical industry.In this work,the particle-wall collision and friction behaviours were analysed by the time-domain statistical and timefrequency joint methods to narrow the high-frequency response range by the initial experiment of free fall for a single particle,interparticle,and multiple particles.Subsequently,verification experiments of PSD characterization in pneumatic flow were performed.First,the quantitative triaxial energy response model that considers the particle size,shape,and mass factors were established.Second,a good agreement of the particle number identification was found between the triaxial vibration energy and mean particle size of 150-550μm.Moreover,the performance with the best accuracy was focused on a range of 42-43 kHz in the x-axis and z-axis and 36.8-38.8 kHz in the y-axis.Finally,the individual particle energy was inversely analysed by the triaxial vibration response within the optimized frequency bands,and the PSD was characterized in real-time by a low error rate,that is,5.2% from the XZ-axis direction of sand(42-43 kHz)and 5.6% from the XYZ-axis of glass(30.9-33.9 kHz,46.2-47.2 kHz,38.3-41.3 kHz for each axis response).Therefore,this research complements the existing approaches for PsD characterization in particulate multiphase flow.
基金supported by the National Center for Research and Development,within the confines of Research and Development Strategic Program Advanced Technologies for Energy Generation Project No.2 Oxy-combustion technology for PC and FBC boilers with CO_2 capture,Agreement No.SP/E/2/66420/10supported by the National Center for Research and Development as a research project development of coal gasification technology for high production of fuels and energy,CzTB 5.2
文摘Particle transport phenomena in small-scale circulating fiuidized beds （CFB） can be simulated using the Euler-Euler, discrete element method, and Euler-Lagrange approaches. In this work, a hybrid Euler-Lagrange model known as the dense discrete phase model （DDPM）, which has common roots with the multiphase particle-in-cell model, was applied in simulating particle transport within a mid-sized experimental CFB facility. Implementation of the DDPM into the commercial ANSYS Fluent CFD package is relatively young in comparison with the granular Eulerian model. For that reason, validation of the DDPM approach against experimental data is still required and is addressed in this paper. Additional difficulties encountered in modeling fluidization processes are connected with long calculation times. To reduce times, the complete boiler models are simplified to include just the combustion chamber. Such simplifications introduce errors in the predicted solid distribution in the boiler. To investigate the conse- quences of model reduction, simulations were made using the simplified and complete pilot geometries and compared with experimental data. All simulations were performed using the ANSYSFLUENT 14.0 package. A set of user defined functions were used in the hybrid DDPM and Euler-Euler approaches to recirculate solid particles.
文摘The lattice Boltzmann method （LBM） is a useful technique for simulating multiphase flows and modeling complex physics. Specifically, we use LBM combined with a direct-forcing （DF） immersed boundary （IB） method to simulate fluid-particle interactions in two-phase particulate flows. Two grids are used in the simulation： a fixed uniform Eulerian grid for the fluid phase and a Lagrangian grid that is attached to and moves with the immersed particles. Forces are calculated at each Lagrangian point. To exchange numerical information between the two grids, discrete delta functions are used. The resulting DF IB-LBM approach is then successfully applied to a variety of reference flows, namely the sedimentation of one and two circular particles in a vertical channel, the sedimentation of one or two spheres in an enclosure, and a neutrally buoyant prolate spheroid in a Couette flow. This last application proves that the developed approach can be used also for non-spherical particles. The three forcing schemes and the different factors affecting the simulation （added mass effect, corrected radius） are also discussed.
