Simulation Of Particulate Flows Research Articles

Particle Flow Simulation of Direct Shear Test of Rock Discontinuities

The stability of rock masses is controlled by the shear behavior of rock discontinuities, and it is hard to investigate the shear behavior of rock discontinuities at micro-scale by using traditional physical test method. With this in mind, Particle Flow Code is used to simulate the direct shear test of rock discontinuities. The PFC model of rock discontinuities is established firstly, and its micro-properties are inversed by using the proposed optimization inversion method based on the asynchronous particle swarm algorithm. Then, the PFC simulation of shear behavior of rock discontinuities is performed. The simulation results show that the number of microcracks gradually increases with the increasement of shear displacement, and the accumulated microcracks result in the shear failure of rock discontinuities.

Numerical Simulation and Analysis of Slope Stability under Load

By biaxial test of soil particle flow simulation program, the corresponding relationship between macro and micro parameters were obtained firstly. And then the slope model was established accord with these parameters. With this model, the slope stability under load were analyzed numerically, the influences of applied loading area on slope stability and damages were compared. Results shown that a slip surface came when slope was broken under a few loaded area, which is called the main slip lines. With the movement of the sliding, other landslide cracks began to appear; when subjected to a large load area, the slope undermining the main slip line was not obvious, but there were multiple landslide fissures, along with the movement of soil, the speed of slope failure increased, and severely damaged instantly.

Feature-Scale Simulations of Particulate Slurry Flows in Chemical Mechanical Polishing by Smoothed Particle Hydrodynamics

AbstractIn 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.

Process Modeling and Particle Flow Simulation of Sand Separation in Cyclone Separator

The Box–Behnken design of mathematical model for cyclone separator was developed for the interactions of particle size, feed load, and pressure drop in the cyclone separator to determine the collection efficiency of sand particles. The collection efficiency of 90% and above was obtained by operating the cyclone separator in pressure drop range of 197–490 Pa for diameter of sand particles in the range of 200–800 µm. The axial and tangential velocities were evaluated using Barth model for the cyclone separator studies. The studies were used to determine the contour regions of pressure fields and various velocity fields using computational fluid dynamics software Fluent for the purpose of flow analysis in the cyclone separator. The static pressure reduces from the wall to the center and negative pressure zone exists at central region due to presence of vortex zone.

Nasal aerodynamics protects brain and lung from inhaled dust in subterranean diggers, Ellobius talpinus.

Inhalation of air-dispersed sub-micrometre and nano-sized particles presents a risk factor for animal and human health. Here, we show that nasal aerodynamics plays a pivotal role in the protection of the subterranean mole vole Ellobius talpinus from an increased exposure to nano-aerosols. Quantitative simulation of particle flow has shown that their deposition on the total surface of the nasal cavity is higher in the mole vole than in a terrestrial rodent Mus musculus (mouse), but lower on the olfactory epithelium. In agreement with simulation results, we found a reduced accumulation of manganese in olfactory bulbs of mole voles in comparison with mice after the inhalation of nano-sized MnCl2 aerosols. We ruled out the possibility that this reduction is owing to a lower transportation from epithelium to brain in the mole vole as intranasal instillations of MnCl2 solution and hydrated nanoparticles of manganese oxide MnO · (H2O)x revealed similar uptake rates for both species. Together, we conclude that nasal geometry contributes to the protection of brain and lung from accumulation of air-dispersed particles in mole voles.

Periodic Boundary Conditions for Discrete Element Method Simulation of Particle Flow in Cylindrical Vessels

The application of the discrete element method (DEM) for industrial process simulation is often limited to two-dimensional slot models for the purpose of reducing the number of particles and hence the computational effort. In this work, a three-dimensional (3D) sector model is proposed with circumferential periodic boundary conditions (PBC) to represent a full 3D model for cylindrical geometries. Two typical processes, i.e. hopper flow and piling, are used to test the sector model. This reveals that the simulated flow features in the 3D sector model with suitable PBC are consistent with those in the full 3D model qualitatively and quantitatively. The proposed sector model can be generally used to investigate granular flow in a full 3D cylindrical geometry in the DEM simulation.

Simulation of particle flow in a bell-less type charging system of a blast furnace using the discrete element method

A three-dimensional model was established by the discrete element method (DEM) to analyze the flow and segregation of particles in a charging process in detail. The simulation results of the burden falling trajectory obtained by the model were compared with the industrial charging measurements to validate the applicability of the model. The flow behavior of particles from the weighing hopper to the top layer of a blast furnace and the heaping behavior were analyzed using this model. A radial segregation index (RSI) was used to evaluate the extent of the size segregation in the charging process. In addition, the influence of the chute inclination angle on the size segregation and burden profile during the charging process was investigated.

WITHDRAWN: Erratum to “The motion of a single heavy sphere in ambient fluid: a benchmark for interface-resolved particulate flow simulations with significant relative velocities” [Int. J. Multiphase Flow 59 (2014) 221-243

WITHDRAWN: Erratum to “The motion of a single heavy sphere in ambient fluid: a benchmark for interface-resolved particulate flow simulations with significant relative velocities” [Int. J. Multiphase Flow 59 (2014) 221-243

A Study on Polymer Particle Flow in a Disk Zone of a Screw-Disk Extruder

Abstract The paper presents the summary of research on polymer melt particle motion trajectories in a disc zone of a screw-disk extruder. We analysed two models of its structure, different in levels of taken simplifications. The analysis includes computer simulations of material particle flow and results of experimental tests to determine the properties of the resultant extrudate. Analysis of the results shows that the motion of melt in the disk zone of a screw-disk extruder is a superposition of pressure and dragged streams. The observed trajectories of polymer particles and relations of mechanical properties and elongation of the molecular chain proved the presence of a stretching effect on polymer molecular chains.

A Sharp Interface Direct Forcing Immersed Boundary Approach for Fully Resolved Simulations of Particulate Flows

In recent years, the immersed boundary method has been well received as an effective approach for the fully resolved simulations of particulate flows. Most immersed boundary approaches for numerical studies of particulate flows in the literature were based on various discrete delta functions for information transfer between the Lagrangian elements of an immersed object and the underlying Eulerian grid. These approaches have some inherent limitations that restrict their wider applications. In this paper, a sharp interface direct forcing immersed boundary approach based on the method proposed by Yang and Stern (Yang and Stern, 2012, “A Simple and Efficient Direct Forcing Immersed Boundary Framework for Fluid-Structure Interactions,” J. Comput. Phys., 231(15), pp. 5029–5061) is given for the fully resolved simulations of particulate flows. This method uses a discrete forcing approach and maintains a sharp profile of the fluid-solid interface. It is not limited to low Reynolds number flows and the immersed boundary discretization can be arbitrary or totally eliminated for particles with analytical shapes. In addition, it is not required to calculate the solid volume fraction in low density ratio problems. A strong coupling scheme is employed for the fluid-solid interaction without including the fluid solver in the predictor-corrector iterative loop. The overall algorithm is highly efficient and very attractive for simulating particulate flows with a wide range of density ratios on relatively coarse grids. Several cases are examined and the results are compared with reference data to demonstrate the simplicity and robustness of our method in particulate flow simulations. These cases include settling and buoyant particles and the interaction of two settling particles showing the kissing-drafting-tumbling phenomenon. Systematic verification studies show that our method is of second-order accuracy on very coarse grids and approaches fourth-order accuracy on finer grids.

Particle Tracking in Large Eddy Simulated Turbulent Channel Flow Using Generalized Lattice Boltzmann Method

The deposition of spherical solid particles with 0.00192 ≤ τ+ ≤ 160.56 in three-dimensional turbulent vertical and horizontal channel flows with friction Reynolds number was studied. A generalized lattice Boltzmann equation (GLBE) was used for computation of instantaneous turbulent flow field for which large eddy simulation (LES) was employed. The subgrid scale (SGS) turbulence effects were simulated through a shear-improved Smagorinsky model (SISM), which can predict turbulent near wall region without any wall function. The Lagrangian particle tracking approach was used, and qualitative distribution of particles in a vertical channel center plane and in a near wall region was presented. It was shown that, in horizontal channels, the rate of deposition is higher than in vertical channels since gravitational sedimentation is the dominant mechanism of deposition on the lower wall. Combination of SISM in GLBE with particle tracking analysis in turbulent channel flow is the novelty of the present work. Since the accuracy of the flow field is essential to correctly predict particles' behavior, a reliable method should be used to simulate the flow field. In the proposed method, the flow field equations are solved locally. The collaboration of this method and particle tracking can be considered a good candidate for simulation of particulate flow.

Using the direct numerical simulation to compute the slip boundary condition of the solid phase in two-fluid model simulations

The simulation of particulate flows for industrial applications often requires the use of two-fluid models, where the solid particles are considered as a separately continuous phase. One of the underlining uncertainties in the use of the two-fluid models in multiphase computations comes from the boundary condition of the solid phase. Typically, the gas or liquid fluid boundary condition at a solid wall is the so called no-slip condition, which has been widely accepted to be valid for single-phase fluid dynamics provided that the Knudsen number is low. However, the boundary condition for the solid phase is not well understood. The no-slip condition at a solid boundary is not a valid assumption for the solid phase. Instead, several researchers advocate a slip condition as a more appropriate boundary condition. However, the question on the selection of an exact slip length or a slip velocity coefficient is still unanswered. Experimental or numerical simulation data are needed in order to determinate the slip boundary condition that is applicable to a two-fluid model. In this paper, we investigate the motion of a number of particles near a vertical solid wall, while the particles are in fluidization by a uniform flow. By applying a direct numerical simulation (DNS), the positions and velocities of a total of 500 particles, initially randomly distributed in a 0.20m×0.80m bed, are being tracked and analyzed at each time step. It is found that the motion of particles is highly unsteady. However, the time- and vertical-space averaged values of the particle velocities converge, yielding velocity profiles that can be used to deduce the particle slip length close to a solid wall. The simulation results show a significant amount downward particle slip close to a vertical wall, with the slip velocity increasing as the fluidization velocity increases. However, a negative slip length of approximately 1.2 particle diameters appears to exist. This slip length was found to be insensitive to the values of the fluidization velocity. We also obtained a power–law relationship between the fluidization velocity and fluid/solid fraction, yielding an exponent coefficient of 4.24 for circular particles. The fluidization of 10,000 particles by a jet flow has also been investigated. Significant slip velocity is also observed at the wall.

Mechanics and response of a surface rock block subjected to pressure fluctuations: A plucking model and its application

Plucking (removal of rock blocks) is often the dominant mechanism for producing a scour hole on riverbeds comprised of heavily jointed rock masses being subjected to pressure fluctuations from a jet flow. This paper explores the mechanics and response of a surface block subjected to pressure fluctuations. First a particle-flow simulation was conducted to demonstrate how repeated pressure fluctuations are able to gradually remove rock bridges in discontinuities surrounding a rock block, if a pressure fluctuation's intensity is substantial. As a consequence, these weak planes may become fully persistent. The block's uplift speed then depends on the pressure differences on the opposite (horizontal) faces, and the frictional resistance of the lateral discontinuities. This paper proposes a theoretical framework to model the mechanics and response of a rock block subjected to a sinusoidal pressure fluctuation. This model can be applied to estimate the development of a scour hole, through plucking, during a specific flood event. An example demonstrates the applicability of the proposed approach in predicting the potential depth of the scour hole.

Large eddy simulation of particulate flow inside a differentially heated cavity

In nuclear safety, some severe accident scenarios lead to the presence of fission products in aerosol form in the closed containment atmosphere. It is important to understand the particle depletion process to estimate the risk of a release of radioactivity to the environment should a containment break occur. As a model for the containment, we use the three-dimensional differentially heated cavity problem. The differentially heated cavity is a cubical box with a hot wall and a cold wall on vertical opposite sides. On the other walls of the cube we have adiabatic boundary conditions. For the velocity field the no-slip boundary condition is applied. The flow of the air in the cavity is described by the Boussinesq equations. The method used to simulate the turbulent flow is the large eddy simulation (LES) where the dynamics of the large eddies is resolved by the computational grid and the small eddies are modelled by the introduction of subgrid scale quantities using a filter function. Particle trajectories are computed using the Lagrangian particle tracking method, including the relevant forces (drag, gravity, thermophoresis). Four different sets with each set containing one million particles and diameters of 10μm, 15μm, 25μm and 35μm are simulated. Simulation results for the flow field and particle sizes from 15μm to 35μm are compared to previous results from direct numerical simulation (DNS). The integration time of the LES is three times longer and the smallest particles have been simulated only in the LES. Particle statistics in the LES and the DNS were similar and the settling rates were practically identical. It was found that for this type of flow no model was necessary for the influence of the unresolved flow scales on the particle motions. This can be explained by the dominant nature of gravity settling compared to turbophoresis which is negligible for the particle sizes of the present study.

Finite element simulation of three-dimensional particulate flows using mixture models

In this paper, we discuss the numerical treatment of three-dimensional mixture models for (semi-)dilute and concentrated suspensions of particles in incompressible fluids. The generalized Navier–Stokes system and the continuity equation for the volume fraction of the disperse phase are discretized using an implicit high-resolution finite element scheme, and maximum principles are enforced using algebraic flux correction. To prevent the volume fractions from exceeding the maximum packing limit, a conservative overshoot limiter is applied to the converged convective fluxes at the end of each time step. A numerical study of the proposed approach is performed for 3D particulate flows over a backward-facing step and in a lid-driven cavity.

An improved version of RIGID for discrete element simulation of particle flows with arbitrarily complex geometries

Traditional discrete element simulations of particle flows in complex geometries rely on the glued particles approximation of geometrical surface. Our recently developed algorithm, RIGID [9], is more robust and accurate than the glued particle method for detecting interactions of spherical particles with arbitrarily shaped walls. However, RIGID is difficult to implement and can be inefficient in identifying particle–vertex or particle–edge contact. To resolve these problems, an improved version of RIGID (RIGID-II) is proposed in this work, which utilizes the basic features of different contact types. By introducing a treatment list to record identification states, the most time consuming step, identification of particle–vertex (edge) contact, is improved significantly. Moreover, such a list can ensure unique identification of particle–vertex or particle–edge contact. Numerical tests show that RIGID-II can predict all contact states accurately. Moreover, it is much more efficient than RIGID and the glued particle method.

Fluid–particle flow simulations using two-way-coupled mesoscale SPH–DEM and validation

First, a meshless simulation method is presented for multiphase fluid–particle flows with a two-way coupled Smoothed Particle Hydrodynamics (SPH) for the fluid and the Discrete Element Method (DEM) for the solid phase. The unresolved fluid model, based on the locally averaged Navier Stokes equations, is expected to be considerably faster than fully resolved models. Furthermore, in contrast to similar mesh-based Discrete Particle Models (DPMs), our purely particle-based method enjoys the flexibility that comes from the lack of a prescribed mesh. It is suitable for problems such as free surface flow or flow around complex, moving and/or intermeshed geometries and is applicable to both dilute and dense particle flows.Second, a comprehensive validation procedure for fluid–particle simulations is presented and applied here to the SPH–DEM method, using simulations of single and multiple particle sedimentation in a 3D fluid column and comparison with analytical models. Millimetre-sized particles are used along with three different test fluids: air, water and a water–glycerol solution. The velocity evolution for a single particle compares well (less than 1% error) with the analytical solution as long as the fluid resolution is coarser than two times the particle diameter. Two more complex multiple particle sedimentation problems (sedimentation of a homogeneous porous block and an inhomogeneous Rayleigh Taylor Instability) are also reproduced well for porosities 0.6⩽∊⩽1.0, although care should be taken in the presence of high porosity gradients.Overall the SPH–DEM method successfully reproduces quantitatively the expected behaviour in these test cases, and promises to be a flexible and accurate tool for other, realistic fluid–particle system simulations (for which other problem-relevant test cases have to be added for validation).

The motion of a single heavy sphere in ambient fluid: A benchmark for interface-resolved particulate flow simulations with significant relative velocities

Detailed data describing the motion of a rigid sphere settling in unperturbed fluid is generated by means of highly-accurate spectral/spectral-element simulations with the purpose of serving as a future benchmark case. A single solid-to-fluid density ratio of 1.5 is chosen, while the value of the Galileo number is varied from 144 to 250 such as to cover the four basic regimes of particle motion (steady vertical, steady oblique, oscillating oblique, chaotic). This corresponds to a range of the particle Reynolds number from 185 to 365. In addition to the particle velocity data, extracts of the fluid velocity field are provided, as well as the pressure distribution on the sphere’s surface. Furthermore, the same solid–fluid system is simulated with a particular non-boundary-conforming approach, i.e. the immersed boundary method proposed by Uhlmann (2005a), using various spatial resolutions. It is shown that the current benchmark case allows to adjust the resolution requirements for a given error tolerance in each flow regime.

A Lagrangian VOF tensorial penalty method for the DNS of resolved particle-laden flows

The direct numerical simulation of particle flows is investigated by a Lagrangian VOF approach and penalty methods of second order convergence in space for incompressible flows interacting with resolved particles on a fixed structured grid. A specific Eulerian volume of fluid method is developed with a Lagrangian tracking of the phase function while the solid and divergence free constraints are ensured implicitly in the motion equations thanks to fictitious domains formulations, adaptive augmented Lagrangian approaches and viscous penalty methods. A specific strategy for handling particle collisions and lubrication effects is also presented. Various dilute particle laden flows are considered for validating the models and numerical methods. Convergence studies are proposed for estimating the time and space convergence orders of the global DNS approach. Finally, two dense particle laden flows are simulated, namely the flow across a fixed array of cylinders and the fluidization of 2133 particles in a vertical pipe. The numerical solutions are compared to existing theoretical and experimental results with success.

Particle Flow Simulation of Slope Instability and Failure

The instability and deformation process of an example of slope is simulated using PFC here. The relationship between macro and micro mechanics parameters is established in the numerical simulation, which determines the calculating parameters.The results of simulation and the example are consistent assessment, which illustrates the effectiveness of calculation, indicates that the PFC method can search the instability and sliding surface and shows the development process of performance failure. During the process, the chain of parallel bond force fractures gradually, but the range where parallel bond fractures is larger than the instable area because of the sliding friction, which improves our understanding of slope instability.