31,212 research outputs found
The discrete multi-hybrid system for the simulation of solid-liquid flows
This study proposes a model based on the combination of Smoothed Particle Hydrodynamics, Coarse Grained Molecular Dynamics and the Discrete Element Method for the simulation of dispersed solid-liquid flows. The model can deal with a large variety of particle types (non-spherical, elastic, breakable, melting, solidifying, swelling), flow conditions (confined, free-surface, microscopic), and scales (from microns to meters). Various examples, ranging from biological fluids to lava flows, are simulated and discussed. In all cases, the model captures the most important features of the flow
The XDEM Multi-physics and Multi-scale Simulation Technology: Review on DEM-CFD Coupling, Methodology and Engineering Applications
The XDEM multi-physics and multi-scale simulation platform roots in the Ex-
tended Discrete Element Method (XDEM) and is being developed at the In- stitute
of Computational Engineering at the University of Luxembourg. The platform is
an advanced multi- physics simulation technology that combines flexibility and
versatility to establish the next generation of multi-physics and multi-scale
simulation tools. For this purpose the simulation framework relies on coupling
various predictive tools based on both an Eulerian and Lagrangian approach.
Eulerian approaches represent the wide field of continuum models while the
Lagrange approach is perfectly suited to characterise discrete phases. Thus,
continuum models include classical simulation tools such as Computa- tional
Fluid Dynamics (CFD) or Finite Element Analysis (FEA) while an ex- tended
configuration of the classical Discrete Element Method (DEM) addresses the
discrete e.g. particulate phase. Apart from predicting the trajectories of
individual particles, XDEM extends the application to estimating the thermo-
dynamic state of each particle by advanced and optimised algorithms. The
thermodynamic state may include temperature and species distributions due to
chemical reaction and external heat sources. Hence, coupling these extended
features with either CFD or FEA opens up a wide range of applications as
diverse as pharmaceutical industry e.g. drug production, agriculture food and
processing industry, mining, construction and agricultural machinery, metals
manufacturing, energy production and systems biology
Discrete element study of liquid-solid slurry flows through constricted channels
Discrete element model is used to simulate the flow of liquid-granule mixtures in an inclined channel containing a linear contraction. All the relevant particle/particle and particle/fluid interactions are included in the numerical model. The presence of the contraction induces different steady morphologies of the solid phase or the mixture depending on whether closed or open channels are used. These flows behave quite differently depending on the upstream Froude number and the contraction size ratio. The model is first validated by comparing with the existing results for dry granular (glass particles) chute flows (Vreman et al., 2007). Then simulations of a chute of glass particles in water flowing in a closed channel are compared to the dry granular case. With the same solid flux at the inlet, the hydrodynamic forces in the liquid-solid mixture induce higher particle solid volume fractions in the part of the flow containing the solid phase. The streamwise particle velocity (resp. depth of the solid phase) has the same evolution along the channel with smaller (larger) values than in the dry granular flow case
Coupled DEM-LBM method for the free-surface simulation of heterogeneous suspensions
The complexity of the interactions between the constituent granular and
liquid phases of a suspension requires an adequate treatment of the
constituents themselves. A promising way for numerical simulations of such
systems is given by hybrid computational frameworks. This is naturally done,
when the Lagrangian description of particle dynamics of the granular phase
finds a correspondence in the fluid description. In this work we employ
extensions of the Lattice-Boltzmann Method for non-Newtonian rheology, free
surfaces, and moving boundaries. The models allows for a full coupling of the
phases, but in a simplified way. An experimental validation is given by an
example of gravity driven flow of a particle suspension
Recent advances in the simulation of particle-laden flows
A substantial number of algorithms exists for the simulation of moving
particles suspended in fluids. However, finding the best method to address a
particular physical problem is often highly non-trivial and depends on the
properties of the particles and the involved fluid(s) together. In this report
we provide a short overview on a number of existing simulation methods and
provide two state of the art examples in more detail. In both cases, the
particles are described using a Discrete Element Method (DEM). The DEM solver
is usually coupled to a fluid-solver, which can be classified as grid-based or
mesh-free (one example for each is given). Fluid solvers feature different
resolutions relative to the particle size and separation. First, a
multicomponent lattice Boltzmann algorithm (mesh-based and with rather fine
resolution) is presented to study the behavior of particle stabilized fluid
interfaces and second, a Smoothed Particle Hydrodynamics implementation
(mesh-free, meso-scale resolution, similar to the particle size) is introduced
to highlight a new player in the field, which is expected to be particularly
suited for flows including free surfaces.Comment: 16 pages, 4 figure
Local Rheology Relation with Variable Yield Stress Ratio across Dry, Wet, Dense, and Dilute Granular Flows
Dry, wet, dense, and dilute granular flows have been previously considered
fundamentally different and thus described by distinct, and in many cases
incompatible, rheologies. We carry out extensive simulations of granular flows,
including wet and dry conditions, various geometries and driving mechanisms
(boundary driven, fluid driven, and gravity driven), many of which are not
captured by standard rheology models. For all simulated conditions, except for
fluid-driven and gravity-driven flows close to the flow threshold, we find that
the Mohr-Coulomb friction coefficient scales with the square root of the
local P\'eclet number provided that the particle diameter exceeds
the particle mean free path. With decreasing and granular
temperature gradient , this general scaling breaks down, leading to a yield
condition with a variable yield stress ratio characterized by
Surface flow profiles for dry and wet granular materials by Particle Tracking Velocimetry; the effect of wall roughness
Two-dimensional Particle Tracking Velocimetry (PTV) is a promising technique
to study the behaviour of granular flows. The aim is to experimentally
determine the free surface width and position of the shear band from the
velocity profile to validate simulations in a split-bottom shear cell geometry.
The position and velocities of scattered tracer particles are tracked as they
move with the bulk flow by analyzing images. We then use a new technique to
extract the continuum velocity field, applying coarse-graining with the
postprocessing toolbox MercuryCG on the discrete experimental PTV data. For
intermediate filling heights, the dependence of the shear (or angular) velocity
on the radial coordinate at the free surface is well fitted by an error
function. From the error function, we get the width and the centre position of
the shear band. We investigate the dependence of these shear band properties on
filling height and rotation frequencies of the shear cell for dry glass beads
for rough and smooth wall surfaces. For rough surfaces, the data agrees with
the existing experimental results and theoretical scaling predictions. For
smooth surfaces, particle-wall slippage is significant and the data deviates
from the predictions. We further study the effect of cohesion on the shear band
properties by using small amount of silicon oil and glycerol as interstitial
liquids with the glass beads. While silicon oil does not lead to big changes,
glycerol changes the shear band properties considerably. The shear band gets
wider and is situated further inward with increasing liquid saturation, due to
the correspondingly increasing trend of particles to stick together
Mesocale approach for fluidized beds
Fluid-particle flows are frequently encountered in industrial facilities and especially in chemical engineering processes. In this work, we focus on fluidized beds, which involve a fluid flow passing upward through a pack of particles with such a velocity that the fluid force acting on particles is larger than their weight
- …