5,528 research outputs found
Regularized lattice Boltzmann Multicomponent models for low Capillary and Reynolds microfluidics flows
We present a regularized version of the color gradient lattice Boltzmann (LB)
scheme for the simulation of droplet formation in microfluidic devices of
experimental relevance. The regularized version is shown to provide
computationally efficient access to Capillary number regimes relevant to
droplet generation via microfluidic devices, such as flow-focusers and the more
recent microfluidic step emulsifier devices.Comment: 9 pages, 5 figure
Kinetic Solvers with Adaptive Mesh in Phase Space
An Adaptive Mesh in Phase Space (AMPS) methodology has been developed for
solving multi-dimensional kinetic equations by the discrete velocity method. A
Cartesian mesh for both configuration (r) and velocity (v) spaces is produced
using a tree of trees data structure. The mesh in r-space is automatically
generated around embedded boundaries and dynamically adapted to local solution
properties. The mesh in v-space is created on-the-fly for each cell in r-space.
Mappings between neighboring v-space trees implemented for the advection
operator in configuration space. We have developed new algorithms for solving
the full Boltzmann and linear Boltzmann equations with AMPS. Several recent
innovations were used to calculate the discrete Boltzmann collision integral
with dynamically adaptive mesh in velocity space: importance sampling,
multi-point projection method, and the variance reduction method. We have
developed an efficient algorithm for calculating the linear Boltzmann collision
integral for elastic and inelastic collisions in a Lorentz gas. New AMPS
technique has been demonstrated for simulations of hypersonic rarefied gas
flows, ion and electron kinetics in weakly ionized plasma, radiation and light
particle transport through thin films, and electron streaming in
semiconductors. We have shown that AMPS allows minimizing the number of cells
in phase space to reduce computational cost and memory usage for solving
challenging kinetic problems
Large-scale grid-enabled lattice-Boltzmann simulations of complex fluid flow in porous media and under shear
Well designed lattice-Boltzmann codes exploit the essentially embarrassingly
parallel features of the algorithm and so can be run with considerable
efficiency on modern supercomputers. Such scalable codes permit us to simulate
the behaviour of increasingly large quantities of complex condensed matter
systems. In the present paper, we present some preliminary results on the large
scale three-dimensional lattice-Boltzmann simulation of binary immiscible fluid
flows through a porous medium derived from digitised x-ray microtomographic
data of Bentheimer sandstone, and from the study of the same fluids under
shear. Simulations on such scales can benefit considerably from the use of
computational steering and we describe our implementation of steering within
the lattice-Boltzmann code, called LB3D, making use of the RealityGrid steering
library. Our large scale simulations benefit from the new concept of capability
computing, designed to prioritise the execution of big jobs on major
supercomputing resources. The advent of persistent computational grids promises
to provide an optimal environment in which to deploy these mesoscale simulation
methods, which can exploit the distributed nature of compute, visualisation and
storage resources to reach scientific results rapidly; we discuss our work on
the grid-enablement of lattice-Boltzmann methods in this context.Comment: 17 pages, 6 figures, accepted for publication in
Phil.Trans.R.Soc.Lond.
Lattice Boltzmann simulations of soft matter systems
This article concerns numerical simulations of the dynamics of particles
immersed in a continuum solvent. As prototypical systems, we consider colloidal
dispersions of spherical particles and solutions of uncharged polymers. After a
brief explanation of the concept of hydrodynamic interactions, we give a
general overview over the various simulation methods that have been developed
to cope with the resulting computational problems. We then focus on the
approach we have developed, which couples a system of particles to a lattice
Boltzmann model representing the solvent degrees of freedom. The standard D3Q19
lattice Boltzmann model is derived and explained in depth, followed by a
detailed discussion of complementary methods for the coupling of solvent and
solute. Colloidal dispersions are best described in terms of extended particles
with appropriate boundary conditions at the surfaces, while particles with
internal degrees of freedom are easier to simulate as an arrangement of mass
points with frictional coupling to the solvent. In both cases, particular care
has been taken to simulate thermal fluctuations in a consistent way. The
usefulness of this methodology is illustrated by studies from our own research,
where the dynamics of colloidal and polymeric systems has been investigated in
both equilibrium and nonequilibrium situations.Comment: Review article, submitted to Advances in Polymer Science. 16 figures,
76 page
Quasiequilibrium lattice Boltzmann models with tunable bulk viscosity for enhancing stability
Taking advantage of a closed-form generalized Maxwell distribution function [ P. Asinari and I. V. Karlin Phys. Rev. E 79 036703 (2009)] and splitting the relaxation to the equilibrium in two steps, an entropic quasiequilibrium (EQE) kinetic model is proposed for the simulation of low Mach number flows, which enjoys both the H theorem and a free-tunable parameter for controlling the bulk viscosity in such a way as to enhance numerical stability in the incompressible flow limit. Moreover, the proposed model admits a simplification based on a proper expansion in the low Mach number limit (LQE model). The lattice Boltzmann implementation of both the EQE and LQE is as simple as that of the standard lattice Bhatnagar-Gross-Krook (LBGK) method, and practical details are reported. Extensive numerical testing with the lid driven cavity flow in two dimensions is presented in order to verify the enhancement of the stability region. The proposed models achieve the same accuracy as the LBGK method with much rougher meshes, leading to an effective computational speed-up of almost three times for EQE and of more than four times for the LQE. Three-dimensional extension of EQE and LQE is also discussed
A lattice Boltzmann model for natural convection in cavities
We study a multiple relaxation time lattice Boltzmann model for natural convection with moment–based boundary conditions. The unknown primary variables of the algorithm at a boundary are found by imposing conditions directly upon hydrodynamic moments, which are then translated into conditions for the discrete velocity distribution functions. The method is formulated so that it is consistent with the second–order implementation of the discrete velocity Boltzmann equations for fluid flow and temperature. Natural convection in square cavities is studied for Rayleigh numbers ranging from 103 to 106. An excellent agreement with benchmark data is observed and the flow fields are shown to converge with second order accuracy
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