In the article, the boundary integral technique is used to salve the hydrodynamic movement. of a train of deformable fluid particles in a tube. When a fluid particle is: in a tube, the total normal stress difference i...In the article, the boundary integral technique is used to salve the hydrodynamic movement. of a train of deformable fluid particles in a tube. When a fluid particle is: in a tube, the total normal stress difference is not constant any more; this force tends to distend and elongate the particle. We find that the difference between the velocity of a deformable fluid particle and a sphere (with the same radius) increases as the distance between the particles decreases, and that the increase in velocity with L'/a' is greater the capillary number, and this increase becomes less pronounced as radius' decreases.展开更多
The turbulent fluid and particle interaction in the turbulent boundary layer for cross how over a cylinder has been experimentally studied. A phase-Doppler anemometer was used to measure the mean and fluctuating veloc...The turbulent fluid and particle interaction in the turbulent boundary layer for cross how over a cylinder has been experimentally studied. A phase-Doppler anemometer was used to measure the mean and fluctuating velocities of both phases. Two size ranges of particles (30 mu m similar to 60 mu m and 80 mu m similar to 150 mu m) at certain concentrations were used for considering the effects of particle sizes on the mean velocity profiles and on the turbulent intensity levels. The measurements clearly demonstrated that the larger particles damped fluid turbulence. For the smaller particles, this damping effect was less noticeable. The measurements further showed a delay in the separation point for two phase turbulent cross how over a cylinder.展开更多
A three-dimensional model for gas-solid flow in a circulating fluidized bed（CFB） riser was developed based on computational particle fluid dynamics（CPFD）.The model was used to simulate the gas-solid flow behavior ...A three-dimensional model for gas-solid flow in a circulating fluidized bed（CFB） riser was developed based on computational particle fluid dynamics（CPFD）.The model was used to simulate the gas-solid flow behavior inside a circulating fluidized bed riser operating at various superficial gas velocities and solids mass fluxes in two fluidization regimes,a dilute phase transport（DPT） regime and a fast fluidization（FF） regime.The simulation results were evaluated based on comparison with experimental data of solids velocity and holdup,obtained from non-invasive automated radioactive particle tracking and gamma-ray tomography techniques,respectively.The agreement of the predicted solids velocity and holdup with experimental data validated the CPFD model for the CFB riser.The model predicted the main features of the gas-solid flows in the two regimes;the uniform dilute phase in the DPT regime,and the coexistence of the dilute phase in the upper region and the dense phase in the lower region in the FF regime.The clustering and solids back mixing in the FF regime were stronger than those in the DPT regime.展开更多
This research assesses the speed of blood flow across blood vessels and more specifically the veins in terms of Reynold’s number (laminar flow vs. turbulence flow) and in terms of overall speed of the blood when bein...This research assesses the speed of blood flow across blood vessels and more specifically the veins in terms of Reynold’s number (laminar flow vs. turbulence flow) and in terms of overall speed of the blood when being injected with high-speed saline particles. The authors propose a novel technique to generate accelerated-waved particles built from saline solution to enable the unblocking of partially-blocked healthy-walled veins, and to restore normal operations of these veins. The novel technique encompasses a pump that accelerates saline solutions into the blood stream of the vein and these oscillated waves break down the fats or deposits inside the veins in order to help the blood to flow freely without any obstruction. This research simulated the vein with blood stream using characteristics of the vein in terms of vein diameter, blood density, venous blood flow, and the viscosity of the blood at the normal body temperature. The speed of the overall blood flow after the injection of the accelerated saline droplet solution was determined as well as the depth of penetration of the accelerated particles in order to cleanse the inside of the vein. Results are promising in terms of not altering significantly the overall speed of the bloodstream and also in terms of efficacy of the length of the vein which is being cleaned using this accelerated particle method.展开更多
Instantaneous flow field and temperature field of the two-phase fluid are measured by particle image velocimetry （PIV） and steady state method during the state of onflow. A turbulent two-phase fluid model of stirred...Instantaneous flow field and temperature field of the two-phase fluid are measured by particle image velocimetry （PIV） and steady state method during the state of onflow. A turbulent two-phase fluid model of stirred bioreactor with punched impeller is established by the computational fluid dynamics （CFD）, using a rotating coordinate system and sliding mesh to describe the relative motion between impeller and baffles. The simulation and experiment results of flow and temperature field prove their warps are less than 10% and the mathematic model can well simulate the fields, which will also provide the study on optimized-design and scale-up of bioreactors with reference value.展开更多
Circulating fluidized bed flue gas desulfurization(CFB-FGD) process has been widely applied in recent years. However, high cost caused by the use of high-quality slaked lime and difficult operation due to the complex ...Circulating fluidized bed flue gas desulfurization(CFB-FGD) process has been widely applied in recent years. However, high cost caused by the use of high-quality slaked lime and difficult operation due to the complex flow field are two issues which have received great attention. Accordingly, a laboratory-scale fluidized bed reactor was constructed to investigate the effects of physical properties and external conditions on desulfurization performance of slaked lime, and the conclusions were tried out in an industrial-scale CFB-FGD tower. After that, a numerical model of the tower was established based on computational particle fluid dynamics(CPFD) and two-film theory. After comparison and validation with actual operation data, the effects of operating parameters on gas-solid distribution and desulfurization characteristics were investigated. The results of experiments and industrial trials showed that the use of slaked lime with a calcium hydroxide content of approximately 80% and particle size greater than 40 μm could significantly reduce the cost of desulfurizer. Simulation results showed that the flow field in the desulfurization tower was skewed under the influence of circulating ash. We obtained optimal operating conditions of 7.5 kg·s^(-1)for the atomized water flow, 70 kg·s^(-1)for circulating ash flow, and 0.56 kg·s^(-1)for slaked lime flow, with desulfurization efficiency reaching 98.19% and the exit flue gas meeting the ultraclean emission and safety requirements. All parameters selected in the simulation were based on engineering examples and had certain application reference significance.展开更多
One of</span><span style="color:red;"> </span><span style="font-family:Verdana;">Newton’s mathematical solutions to a hypothetical orbital problem, recently verified by an ...One of</span><span style="color:red;"> </span><span style="font-family:Verdana;">Newton’s mathematical solutions to a hypothetical orbital problem, recently verified by an independent physics model, is applied to the fluid particle motion in shallow water surface gravity waves. What is the functional form of the central force, with origin at the ellipse’s center, which will keep a body in the orbit? Newton found out it is the spring force, which is linear. All fluid particles in shallow water waves move in ellipses. By a superposition of solutions in a linear problem, the application of Newton’s result to shallow water waves is combined with a feature not noticed by Newton: the orbital period is independent of the semi-major and semi-minor axes. Two conclusions reached are that the wave period of shoaling waves should be constant and that there is no friction in these waves.展开更多
1.Introduction Computational Fluid Dynamics-Discrete Element Method(CFD-DEM)is a powerful tool for simulating dense gas-solid reacting flows,which is essential in combustion,metallurgy,and waste management.Traditional...1.Introduction Computational Fluid Dynamics-Discrete Element Method(CFD-DEM)is a powerful tool for simulating dense gas-solid reacting flows,which is essential in combustion,metallurgy,and waste management.Traditional methods face challenges in CFD-DEM modeling of dense gas-solid flows due to multi-scale characteristics,limiting resolution and creating simulation bottlenecks.By integrating fluid dynamics and particle behavior,it optimizes industrial processes.This review highlights advancements,applications,and challenges,emphasizing its role in sustainable engineering.展开更多
Lagrangian and Eulerian statistics are obtained from the direct numerical simulation of a turbulent channel flow. The Reynolds number is obtained to be Reτ = 100 （based on friction velocity and channel half-height）...Lagrangian and Eulerian statistics are obtained from the direct numerical simulation of a turbulent channel flow. The Reynolds number is obtained to be Reτ = 100 （based on friction velocity and channel half-height）. The Lagrangian time microscales are compared to their Eulerian equivalents. It is found that the Lagrangian time microscales equal the Eulerian time microscales at the wall, but they are consistently larger than the Eulerian away from the wall. The Eulerian time scales are also found to be scaled by the propagation velocity rather than the mean velocity. The ratio of the Lagrangian to the Eulerian time microscales is found to be nearly constant away from the wall （y^＋ 〉 40）.展开更多
Conventional model tests and centrifuge tests are frequently used to investigate seepage erosion. However, the centrifugal test method may not be efficient according to the results of hydraulic conductivity tests and ...Conventional model tests and centrifuge tests are frequently used to investigate seepage erosion. However, the centrifugal test method may not be efficient according to the results of hydraulic conductivity tests and piping erosion tests. The reason why seepage deformation in model tests may deviate from similarity was first discussed in this work. Then, the similarity criterion for seepage deformation in porous media was improved based on the extended Darcy-Brinkman-Forchheimer equation. Finally, the coupled particle flow code–computational fluid dynamics(PFC-CFD) model at the mesoscopic level was proposed to verify the derived similarity criterion. The proposed model maximizes its potential to simulate seepage erosion via the discrete element method and satisfy the similarity criterion by adjusting particle size. The numerical simulations achieved identical results with the prototype, thus indicating that the PFC-CFD model that satisfies the improved similarity criterion can accurately reproduce the processes of seepage erosion at the mesoscopic level.展开更多
Impulse waves generated by the collapse of pillar-shaped rock masses in Three Gorges, China,have attracted the attention of both researchers and local authorities owing to their catastrophic consequences. In this work...Impulse waves generated by the collapse of pillar-shaped rock masses in Three Gorges, China,have attracted the attention of both researchers and local authorities owing to their catastrophic consequences. In this work, particle imaging velocimetry(PIV) was used to study impulse waves generated by the collapse of granular pillars during a series of physical experiments. Subsequently, the scenes of particles collapsing into water and the resulting impulse waves were analysed in terms of the solid/fluid fields. The energy obtained by the water during this process is mainly derived from the volume encroachment and continuous thrusting of particles.As indicated by the experimental results, as the aspect ratio(a) of the pillar and water depth increased, the potential energy of the granular pillar became more prone to reduction, whereas the efficiency of energy conversion to the liquid phase reduced. At constant water depth and granular pillar width, the maximum amplitude generated by the collapse of the granular pillar remained essentially the same(i.e., "saturation"was achieved) once the aspect ratio exceeded a certain threshold. The maximum impulse wave(the primary wave) formed before the main body of particles collapsed, resulting in the "saturation" of the maximum amplitude. When the kinetic energy of the particles reaches the maximum, the ratio of energy dissipation of the particles is the lowest;as the energy of water reaches the maximum, the particle collapse process does not end. The dynamic analysis of the impulse waves generated by the collapse of granular pillars provides a new approach to obtain an in-depth understanding of landslides and impulse waves. This can provide technical guidelines for disaster prevention and mitigation of impulse waves generated by bank collapse or coastline collapse.展开更多
In microfluidic technology, dielectrophoresis(DEP) is commonly used to manipulate particles. In this work, the fluid–particle interactions in a microfluidic system are investigated numerically by a finite difference ...In microfluidic technology, dielectrophoresis(DEP) is commonly used to manipulate particles. In this work, the fluid–particle interactions in a microfluidic system are investigated numerically by a finite difference method(FDM) for electric field distribution and a lattice Boltzmann method(LBM) for the fluid flow. In this system, efficient particle manipulation may be realized by combining DEP and field-modulating vortex. The influence of the density(ρ_(p)), radius(γ), and initial position of the particle in the y direction(y_(p0)), and the slip velocity(u_(0)) on the particle manipulation are studied systematically. It is found that compared with the particle without action of DEP force, the particle subjected to a DEP force may be captured by the vortex over a wider range of parameters. In the y direction, as ρ_(p) or γ increases, the particle can be captured more easily by the vortex since it is subjected to a stronger DEP force. When u_(0) is low, particle is more likely to be captured due to the vortex–particle interaction. Furthermore, the flow field around the particle is analyzed to explore the underlying mechanism. The results obtained in the present study may provide theoretical support for engineering applications of field-controlled vortices to manipulate particles.展开更多
The correction of buoyancy effects is tackled for particles moving close to a singular corner in creeping flow conditions.A few density-mismatched particle trajectories are used to reconstruct the dynamics of a neutra...The correction of buoyancy effects is tackled for particles moving close to a singular corner in creeping flow conditions.A few density-mismatched particle trajectories are used to reconstruct the dynamics of a neutrally-buoyant particle all over the target domain.We propose to take advantage of the dissipative dynamics of density-mismatched particles in order to probe the target domain.Thereafter,we retrieve the neutrally-buoyant particle flow all over the domain by reconstructing the phase space of the density-mismatched particulate flow and taking the limit of the particle-to-fluid density ratio tending to one.The robustness of such an approach is demonstrated by deliberately ill-conditioning the reconstruction operator.In fact,we show that our algorithm well performs even when we rely on qualitatively-different density-mismatched orbit topologies or on bundles of close trajectories rather than homogeneously distributed orbits.Potential applications to microfluidics and improvements of the proposed algorithm are finally discussed.展开更多
1. Introduction Supported by the Sino-German Center for Research Promotion, and organized jointly by the National Natural Science Foundation of China (NSFC) and the German Research Foundation (DFG), the third Sino-Ger...1. Introduction Supported by the Sino-German Center for Research Promotion, and organized jointly by the National Natural Science Foundation of China (NSFC) and the German Research Foundation (DFG), the third Sino-German workshop on particle fluid systems was held on Oct. 24-31, 2004 in Beijing, China, following the two previous successful workshops held on Aug. 30-31,1999 in Hamburg, Germany (Li and Werther, Chem. Eng. Technol., 23(4), 378, 2000) and May 18-19, 2001 in Beijing, China (Li, Ge, Werther and Bruhns, Chem. Eng. Technol., 24(11), 1097, 2001). Thirty-one scientists from China, Germany, Japan and The Netherlands came together for interdisciplinary discussion over the core problem of multi-phase reaction systems in the name of "Chemical and Physical Interactions between Particles and Fluids".展开更多
Spectral element methods (SEM) are superior to general finite element methods (FEM) in achieving high order accuracy through p-type refinement. Owing to orthogonal polynomials in both expansion and test functions, the...Spectral element methods (SEM) are superior to general finite element methods (FEM) in achieving high order accuracy through p-type refinement. Owing to orthogonal polynomials in both expansion and test functions, the discretization errors in SEM could be reduced exponentially to machine zero so that the spectral convergence rate can be achieved. Inherited the advantage of FEM, SEM can enhance resolution via both h-type and p-type mesh-refinement. A penalty method was utilized to compute force fields in particulate flows involving freely moving rigid particles. Results were analyzed and comparisons were made;therefore, this penalty-implemented SEM was proven to be a viable method for two-phase flow problems.展开更多
This paper is concerned with the dispersion of particles on the fluid-liquid interface. In a previous study we have shown that when small particles, e.g., flour, pollen, glass beads, etc., contact an air-liquid interf...This paper is concerned with the dispersion of particles on the fluid-liquid interface. In a previous study we have shown that when small particles, e.g., flour, pollen, glass beads, etc., contact an air-liquid interface, they disperse rapidly as if they were in an explosion. The rapid dispersion is due to the fact that the capillary force pulls particles into the interface causing them to accelerate to a large velocity. In this paper we show that motion of particles normal to the interface is inertia dominated; they oscillate vertically about their equilibrium position before coming to rest under viscous drag. This vertical motion of a particle causes a radially-outward lateral （secondary） flow on the interface that causes nearby particles to move away. The dispersion on a liquid-liquid interface, which is the primary focus of this study, was relatively weaker than on an air-liquid interface, and occurred over a longer period of time. When falling through an upper liquid the particles have a slower velocity than when falling through air because the liquid has a greater viscosity. Another difference for the liquid-liquid interface is that the separation of particles begins in the upper liquid before the particles reach the interface. The rate of dispersion depended on the size of the particles, the densities of the particle and liquids, the viscosities of the liquids involved, and the contact angle. For small particles, partial pinning and hysteresis of the three-phase contact line on the surface of the particle during adsorption on liquid-liquid interfaces was also important. The frequency of oscillation of particles about their floating equilibrium increased with decreasing particle size on both air-water and liquid-liquid interfaces, and the time to reach equilibrium decreased with decreasing particle size. These results are in agreement with our analysis.展开更多
A computational particle fluid-dynamics model coupled with an energy-minimization multi-scale(EMMS)drag model was applied to investigate the influence of particle-size distribution on the hydrodynamics of a three-dime...A computational particle fluid-dynamics model coupled with an energy-minimization multi-scale(EMMS)drag model was applied to investigate the influence of particle-size distribution on the hydrodynamics of a three-dimensional full-loop circulating fluidized bed.Different particle systems,including one monodisperse and two polydisperse cases,were investigated.The numerical model was validated by comparing its results with the experimental axial voidage distribution and solid mass flux.The EMMS drag model had a high accuracy in the computational particle fluid-dynamics simulation of the three-dimensional full-loop circulating fluidized bed.The total number of parcels in the system(Np)influenced the axial voidage distribution in the riser,especially at the lower part of the riser.Additional numerical simulation results showed that axial segregation by size was predicted in the two polydisperse cases and the segregation size increased with an increase in the number of size classes.The axial voidage distribution at the lower portion of the riser was significantly influenced by particle-size distribution.However,radial segregation could only be correctly predicted in the upper region of the riser in the polydisperse case of three solid species.展开更多
The performance of a circulating fluidized bed strongly depends on its parameter settings,including that of riser geometry.In this study,a laboratory-scale circulating fluidized bed with three different riser geometri...The performance of a circulating fluidized bed strongly depends on its parameter settings,including that of riser geometry.In this study,a laboratory-scale circulating fluidized bed with three different riser geometries(circular,square,and rectangular)that had the same cross-sectional area and height was operated under two static bed heights(20,and 35 cm).Electrical capacitance tomography was combined with differential pressure transducers and an optical-fiber probe to measure the solids'volume fraction,differential pressure fluctuations,and radial particle concentration variations.Computational particle fluid dynamics simulations were also performed.The results showed that single bubbles appeared in the bottom region of the circular and square risers and double bubbles in the bottom region of the rectangular riser.The autocorrelation of capacitance signals was periodic for the circular and square risers and non-periodic for the rectangular riser.The radial particle concentration profiles showed a single-core annulus structure in the circular and square risers,but a double-core annulus structure along the long side and single-core annulus structure along the short side in the rectangular riser.Shannon entropy analysis showed that fluidization was less disordered and most predictable for the rectangular riser.展开更多
A cold flow model of an 8 MW dual fluidized bed （DFB） system is simulated using the commercial compu- tational particle fluid dynamics （CPFD） software package Barracuda. The DFB system comprises a bubbling bed con...A cold flow model of an 8 MW dual fluidized bed （DFB） system is simulated using the commercial compu- tational particle fluid dynamics （CPFD） software package Barracuda. The DFB system comprises a bubbling bed connected to a fast fluidized bed with the bed material circulating between them. As the hydrodynam- ics in hot DFB plants are complex because of high temperatures and many chemical reaction processes, cold flow models are used. Performing numerical simulations of cold flows enables a focus on the hydro- dynamics as the chemistry and heat and mass transfer processes can be put aside. The drag law has a major influence on the hydrodynamics, and therefore its influence on pressure, particle distribution, and bed material recirculation rate is calculated using Barracuda and its results are compared with experimental results. The drag laws used were energy-minimization multiscale （EMMS）, Ganser, Turton-Levenspiel, and a combination of Wen-Yu]Ergun. Eleven operating points were chosen for that study and each was calculated with the aforementioned drag laws. The EMMS drag law best predicted the pressure and dis- tribution of the bed material in the different parts of the DFB system. For predicting the bed material recirculation rate, the Ganser drag law showed the best results. However, the drag laws often were not able to predict the experimentally found trends of the bed material recirculation rate. Indeed, the drag law significantly influences the hydrodynamic outcomes in a DFB system and must be chosen carefully to obtain meaningful simulation results. More research may enable recommendations as to which drag law is useful in simulations ofa DFB system with CPFD.展开更多
文摘In the article, the boundary integral technique is used to salve the hydrodynamic movement. of a train of deformable fluid particles in a tube. When a fluid particle is: in a tube, the total normal stress difference is not constant any more; this force tends to distend and elongate the particle. We find that the difference between the velocity of a deformable fluid particle and a sphere (with the same radius) increases as the distance between the particles decreases, and that the increase in velocity with L'/a' is greater the capillary number, and this increase becomes less pronounced as radius' decreases.
基金The project supported by the National Natural Science Foundation of China
文摘The turbulent fluid and particle interaction in the turbulent boundary layer for cross how over a cylinder has been experimentally studied. A phase-Doppler anemometer was used to measure the mean and fluctuating velocities of both phases. Two size ranges of particles (30 mu m similar to 60 mu m and 80 mu m similar to 150 mu m) at certain concentrations were used for considering the effects of particle sizes on the mean velocity profiles and on the turbulent intensity levels. The measurements clearly demonstrated that the larger particles damped fluid turbulence. For the smaller particles, this damping effect was less noticeable. The measurements further showed a delay in the separation point for two phase turbulent cross how over a cylinder.
基金support by the National Basic Research Program (Grant No. 2010CB226906,and 2012CB215000)
文摘A three-dimensional model for gas-solid flow in a circulating fluidized bed（CFB） riser was developed based on computational particle fluid dynamics（CPFD）.The model was used to simulate the gas-solid flow behavior inside a circulating fluidized bed riser operating at various superficial gas velocities and solids mass fluxes in two fluidization regimes,a dilute phase transport（DPT） regime and a fast fluidization（FF） regime.The simulation results were evaluated based on comparison with experimental data of solids velocity and holdup,obtained from non-invasive automated radioactive particle tracking and gamma-ray tomography techniques,respectively.The agreement of the predicted solids velocity and holdup with experimental data validated the CPFD model for the CFB riser.The model predicted the main features of the gas-solid flows in the two regimes;the uniform dilute phase in the DPT regime,and the coexistence of the dilute phase in the upper region and the dense phase in the lower region in the FF regime.The clustering and solids back mixing in the FF regime were stronger than those in the DPT regime.
文摘This research assesses the speed of blood flow across blood vessels and more specifically the veins in terms of Reynold’s number (laminar flow vs. turbulence flow) and in terms of overall speed of the blood when being injected with high-speed saline particles. The authors propose a novel technique to generate accelerated-waved particles built from saline solution to enable the unblocking of partially-blocked healthy-walled veins, and to restore normal operations of these veins. The novel technique encompasses a pump that accelerates saline solutions into the blood stream of the vein and these oscillated waves break down the fats or deposits inside the veins in order to help the blood to flow freely without any obstruction. This research simulated the vein with blood stream using characteristics of the vein in terms of vein diameter, blood density, venous blood flow, and the viscosity of the blood at the normal body temperature. The speed of the overall blood flow after the injection of the accelerated saline droplet solution was determined as well as the depth of penetration of the accelerated particles in order to cleanse the inside of the vein. Results are promising in terms of not altering significantly the overall speed of the bloodstream and also in terms of efficacy of the length of the vein which is being cleaned using this accelerated particle method.
基金This project is supported by Provincial Science Technology Committee of Jiangsu China(No.BJ99025).
文摘Instantaneous flow field and temperature field of the two-phase fluid are measured by particle image velocimetry （PIV） and steady state method during the state of onflow. A turbulent two-phase fluid model of stirred bioreactor with punched impeller is established by the computational fluid dynamics （CFD）, using a rotating coordinate system and sliding mesh to describe the relative motion between impeller and baffles. The simulation and experiment results of flow and temperature field prove their warps are less than 10% and the mathematic model can well simulate the fields, which will also provide the study on optimized-design and scale-up of bioreactors with reference value.
基金supported by National Natural Science Foundation of China(52336005 and 52106133).
文摘Circulating fluidized bed flue gas desulfurization(CFB-FGD) process has been widely applied in recent years. However, high cost caused by the use of high-quality slaked lime and difficult operation due to the complex flow field are two issues which have received great attention. Accordingly, a laboratory-scale fluidized bed reactor was constructed to investigate the effects of physical properties and external conditions on desulfurization performance of slaked lime, and the conclusions were tried out in an industrial-scale CFB-FGD tower. After that, a numerical model of the tower was established based on computational particle fluid dynamics(CPFD) and two-film theory. After comparison and validation with actual operation data, the effects of operating parameters on gas-solid distribution and desulfurization characteristics were investigated. The results of experiments and industrial trials showed that the use of slaked lime with a calcium hydroxide content of approximately 80% and particle size greater than 40 μm could significantly reduce the cost of desulfurizer. Simulation results showed that the flow field in the desulfurization tower was skewed under the influence of circulating ash. We obtained optimal operating conditions of 7.5 kg·s^(-1)for the atomized water flow, 70 kg·s^(-1)for circulating ash flow, and 0.56 kg·s^(-1)for slaked lime flow, with desulfurization efficiency reaching 98.19% and the exit flue gas meeting the ultraclean emission and safety requirements. All parameters selected in the simulation were based on engineering examples and had certain application reference significance.
文摘One of</span><span style="color:red;"> </span><span style="font-family:Verdana;">Newton’s mathematical solutions to a hypothetical orbital problem, recently verified by an independent physics model, is applied to the fluid particle motion in shallow water surface gravity waves. What is the functional form of the central force, with origin at the ellipse’s center, which will keep a body in the orbit? Newton found out it is the spring force, which is linear. All fluid particles in shallow water waves move in ellipses. By a superposition of solutions in a linear problem, the application of Newton’s result to shallow water waves is combined with a feature not noticed by Newton: the orbital period is independent of the semi-major and semi-minor axes. Two conclusions reached are that the wave period of shoaling waves should be constant and that there is no friction in these waves.
文摘1.Introduction Computational Fluid Dynamics-Discrete Element Method(CFD-DEM)is a powerful tool for simulating dense gas-solid reacting flows,which is essential in combustion,metallurgy,and waste management.Traditional methods face challenges in CFD-DEM modeling of dense gas-solid flows due to multi-scale characteristics,limiting resolution and creating simulation bottlenecks.By integrating fluid dynamics and particle behavior,it optimizes industrial processes.This review highlights advancements,applications,and challenges,emphasizing its role in sustainable engineering.
文摘Lagrangian and Eulerian statistics are obtained from the direct numerical simulation of a turbulent channel flow. The Reynolds number is obtained to be Reτ = 100 （based on friction velocity and channel half-height）. The Lagrangian time microscales are compared to their Eulerian equivalents. It is found that the Lagrangian time microscales equal the Eulerian time microscales at the wall, but they are consistently larger than the Eulerian away from the wall. The Eulerian time scales are also found to be scaled by the propagation velocity rather than the mean velocity. The ratio of the Lagrangian to the Eulerian time microscales is found to be nearly constant away from the wall （y^＋ 〉 40）.
基金Project(51309086)supported by the National Natural Science Foundation of ChinaProject(20110094120002)supported by the Ministry Education Foundation of ChinaProjects(2014B04914,2011B07214)supported by the Fundamental Research Funds for the Central Universities,China
文摘Conventional model tests and centrifuge tests are frequently used to investigate seepage erosion. However, the centrifugal test method may not be efficient according to the results of hydraulic conductivity tests and piping erosion tests. The reason why seepage deformation in model tests may deviate from similarity was first discussed in this work. Then, the similarity criterion for seepage deformation in porous media was improved based on the extended Darcy-Brinkman-Forchheimer equation. Finally, the coupled particle flow code–computational fluid dynamics(PFC-CFD) model at the mesoscopic level was proposed to verify the derived similarity criterion. The proposed model maximizes its potential to simulate seepage erosion via the discrete element method and satisfy the similarity criterion by adjusting particle size. The numerical simulations achieved identical results with the prototype, thus indicating that the PFC-CFD model that satisfies the improved similarity criterion can accurately reproduce the processes of seepage erosion at the mesoscopic level.
基金supported by the National Key R&D Program of China (ID:2018YFC1504806 & 2018YFC1504803)。
文摘Impulse waves generated by the collapse of pillar-shaped rock masses in Three Gorges, China,have attracted the attention of both researchers and local authorities owing to their catastrophic consequences. In this work, particle imaging velocimetry(PIV) was used to study impulse waves generated by the collapse of granular pillars during a series of physical experiments. Subsequently, the scenes of particles collapsing into water and the resulting impulse waves were analysed in terms of the solid/fluid fields. The energy obtained by the water during this process is mainly derived from the volume encroachment and continuous thrusting of particles.As indicated by the experimental results, as the aspect ratio(a) of the pillar and water depth increased, the potential energy of the granular pillar became more prone to reduction, whereas the efficiency of energy conversion to the liquid phase reduced. At constant water depth and granular pillar width, the maximum amplitude generated by the collapse of the granular pillar remained essentially the same(i.e., "saturation"was achieved) once the aspect ratio exceeded a certain threshold. The maximum impulse wave(the primary wave) formed before the main body of particles collapsed, resulting in the "saturation" of the maximum amplitude. When the kinetic energy of the particles reaches the maximum, the ratio of energy dissipation of the particles is the lowest;as the energy of water reaches the maximum, the particle collapse process does not end. The dynamic analysis of the impulse waves generated by the collapse of granular pillars provides a new approach to obtain an in-depth understanding of landslides and impulse waves. This can provide technical guidelines for disaster prevention and mitigation of impulse waves generated by bank collapse or coastline collapse.
基金Project supported by the National Natural Science Foundation of China (Granmt Nos. 11572139, 11872187, and 12072125)。
文摘In microfluidic technology, dielectrophoresis(DEP) is commonly used to manipulate particles. In this work, the fluid–particle interactions in a microfluidic system are investigated numerically by a finite difference method(FDM) for electric field distribution and a lattice Boltzmann method(LBM) for the fluid flow. In this system, efficient particle manipulation may be realized by combining DEP and field-modulating vortex. The influence of the density(ρ_(p)), radius(γ), and initial position of the particle in the y direction(y_(p0)), and the slip velocity(u_(0)) on the particle manipulation are studied systematically. It is found that compared with the particle without action of DEP force, the particle subjected to a DEP force may be captured by the vortex over a wider range of parameters. In the y direction, as ρ_(p) or γ increases, the particle can be captured more easily by the vortex since it is subjected to a stronger DEP force. When u_(0) is low, particle is more likely to be captured due to the vortex–particle interaction. Furthermore, the flow field around the particle is analyzed to explore the underlying mechanism. The results obtained in the present study may provide theoretical support for engineering applications of field-controlled vortices to manipulate particles.
文摘The correction of buoyancy effects is tackled for particles moving close to a singular corner in creeping flow conditions.A few density-mismatched particle trajectories are used to reconstruct the dynamics of a neutrally-buoyant particle all over the target domain.We propose to take advantage of the dissipative dynamics of density-mismatched particles in order to probe the target domain.Thereafter,we retrieve the neutrally-buoyant particle flow all over the domain by reconstructing the phase space of the density-mismatched particulate flow and taking the limit of the particle-to-fluid density ratio tending to one.The robustness of such an approach is demonstrated by deliberately ill-conditioning the reconstruction operator.In fact,we show that our algorithm well performs even when we rely on qualitatively-different density-mismatched orbit topologies or on bundles of close trajectories rather than homogeneously distributed orbits.Potential applications to microfluidics and improvements of the proposed algorithm are finally discussed.
文摘1. Introduction Supported by the Sino-German Center for Research Promotion, and organized jointly by the National Natural Science Foundation of China (NSFC) and the German Research Foundation (DFG), the third Sino-German workshop on particle fluid systems was held on Oct. 24-31, 2004 in Beijing, China, following the two previous successful workshops held on Aug. 30-31,1999 in Hamburg, Germany (Li and Werther, Chem. Eng. Technol., 23(4), 378, 2000) and May 18-19, 2001 in Beijing, China (Li, Ge, Werther and Bruhns, Chem. Eng. Technol., 24(11), 1097, 2001). Thirty-one scientists from China, Germany, Japan and The Netherlands came together for interdisciplinary discussion over the core problem of multi-phase reaction systems in the name of "Chemical and Physical Interactions between Particles and Fluids".
文摘Spectral element methods (SEM) are superior to general finite element methods (FEM) in achieving high order accuracy through p-type refinement. Owing to orthogonal polynomials in both expansion and test functions, the discretization errors in SEM could be reduced exponentially to machine zero so that the spectral convergence rate can be achieved. Inherited the advantage of FEM, SEM can enhance resolution via both h-type and p-type mesh-refinement. A penalty method was utilized to compute force fields in particulate flows involving freely moving rigid particles. Results were analyzed and comparisons were made;therefore, this penalty-implemented SEM was proven to be a viable method for two-phase flow problems.
文摘This paper is concerned with the dispersion of particles on the fluid-liquid interface. In a previous study we have shown that when small particles, e.g., flour, pollen, glass beads, etc., contact an air-liquid interface, they disperse rapidly as if they were in an explosion. The rapid dispersion is due to the fact that the capillary force pulls particles into the interface causing them to accelerate to a large velocity. In this paper we show that motion of particles normal to the interface is inertia dominated; they oscillate vertically about their equilibrium position before coming to rest under viscous drag. This vertical motion of a particle causes a radially-outward lateral （secondary） flow on the interface that causes nearby particles to move away. The dispersion on a liquid-liquid interface, which is the primary focus of this study, was relatively weaker than on an air-liquid interface, and occurred over a longer period of time. When falling through an upper liquid the particles have a slower velocity than when falling through air because the liquid has a greater viscosity. Another difference for the liquid-liquid interface is that the separation of particles begins in the upper liquid before the particles reach the interface. The rate of dispersion depended on the size of the particles, the densities of the particle and liquids, the viscosities of the liquids involved, and the contact angle. For small particles, partial pinning and hysteresis of the three-phase contact line on the surface of the particle during adsorption on liquid-liquid interfaces was also important. The frequency of oscillation of particles about their floating equilibrium increased with decreasing particle size on both air-water and liquid-liquid interfaces, and the time to reach equilibrium decreased with decreasing particle size. These results are in agreement with our analysis.
基金This work was financially supported by the National Natural Science Foundation of China through contract No.91634109 and No.51676158the National Key Research and Development Program of China(2016YFB0600102).
文摘A computational particle fluid-dynamics model coupled with an energy-minimization multi-scale(EMMS)drag model was applied to investigate the influence of particle-size distribution on the hydrodynamics of a three-dimensional full-loop circulating fluidized bed.Different particle systems,including one monodisperse and two polydisperse cases,were investigated.The numerical model was validated by comparing its results with the experimental axial voidage distribution and solid mass flux.The EMMS drag model had a high accuracy in the computational particle fluid-dynamics simulation of the three-dimensional full-loop circulating fluidized bed.The total number of parcels in the system(Np)influenced the axial voidage distribution in the riser,especially at the lower part of the riser.Additional numerical simulation results showed that axial segregation by size was predicted in the two polydisperse cases and the segregation size increased with an increase in the number of size classes.The axial voidage distribution at the lower portion of the riser was significantly influenced by particle-size distribution.However,radial segregation could only be correctly predicted in the upper region of the riser in the polydisperse case of three solid species.
基金The authors are grateful for support from the National Natu-ral Science Foundation of China(Grant No.61771455)the Chinese Academy of Sciences Interdisciplinary Innovation Team,and a Royal Society Newton Advanced Fellowship(No.NA170124).
文摘The performance of a circulating fluidized bed strongly depends on its parameter settings,including that of riser geometry.In this study,a laboratory-scale circulating fluidized bed with three different riser geometries(circular,square,and rectangular)that had the same cross-sectional area and height was operated under two static bed heights(20,and 35 cm).Electrical capacitance tomography was combined with differential pressure transducers and an optical-fiber probe to measure the solids'volume fraction,differential pressure fluctuations,and radial particle concentration variations.Computational particle fluid dynamics simulations were also performed.The results showed that single bubbles appeared in the bottom region of the circular and square risers and double bubbles in the bottom region of the rectangular riser.The autocorrelation of capacitance signals was periodic for the circular and square risers and non-periodic for the rectangular riser.The radial particle concentration profiles showed a single-core annulus structure in the circular and square risers,but a double-core annulus structure along the long side and single-core annulus structure along the short side in the rectangular riser.Shannon entropy analysis showed that fluidization was less disordered and most predictable for the rectangular riser.
文摘A cold flow model of an 8 MW dual fluidized bed （DFB） system is simulated using the commercial compu- tational particle fluid dynamics （CPFD） software package Barracuda. The DFB system comprises a bubbling bed connected to a fast fluidized bed with the bed material circulating between them. As the hydrodynam- ics in hot DFB plants are complex because of high temperatures and many chemical reaction processes, cold flow models are used. Performing numerical simulations of cold flows enables a focus on the hydro- dynamics as the chemistry and heat and mass transfer processes can be put aside. The drag law has a major influence on the hydrodynamics, and therefore its influence on pressure, particle distribution, and bed material recirculation rate is calculated using Barracuda and its results are compared with experimental results. The drag laws used were energy-minimization multiscale （EMMS）, Ganser, Turton-Levenspiel, and a combination of Wen-Yu]Ergun. Eleven operating points were chosen for that study and each was calculated with the aforementioned drag laws. The EMMS drag law best predicted the pressure and dis- tribution of the bed material in the different parts of the DFB system. For predicting the bed material recirculation rate, the Ganser drag law showed the best results. However, the drag laws often were not able to predict the experimentally found trends of the bed material recirculation rate. Indeed, the drag law significantly influences the hydrodynamic outcomes in a DFB system and must be chosen carefully to obtain meaningful simulation results. More research may enable recommendations as to which drag law is useful in simulations ofa DFB system with CPFD.
