14,497 research outputs found
Entropic Lattice Boltzmann Method for Moving and Deforming Geometries in Three Dimensions
Entropic lattice Boltzmann methods have been developed to alleviate intrinsic
stability issues of lattice Boltzmann models for under-resolved simulations.
Its reliability in combination with moving objects was established for various
laminar benchmark flows in two dimensions in our previous work Dorschner et al.
[11] as well as for three dimensional one-way coupled simulations of
engine-type geometries in Dorschner et al. [12] for flat moving walls. The
present contribution aims to fully exploit the advantages of entropic lattice
Boltzmann models in terms of stability and accuracy and extends the methodology
to three-dimensional cases including two-way coupling between fluid and
structure, turbulence and deformable meshes. To cover this wide range of
applications, the classical benchmark of a sedimenting sphere is chosen first
to validate the general two-way coupling algorithm. Increasing the complexity,
we subsequently consider the simulation of a plunging SD7003 airfoil at a
Reynolds number of Re = 40000 and finally, to access the model's performance
for deforming meshes, we conduct a two-way coupled simulation of a
self-propelled anguilliform swimmer. These simulations confirm the viability of
the new fluid-structure interaction lattice Boltzmann algorithm to simulate
flows of engineering relevance.Comment: submitted to Journal of Computational Physic
Developing A Stable Lattice Boltzmann For Computational Dynamics Applications
The lattice Boltzmann method (LBM) has been employed to investigate the temporal and spatial characteristics of complex flows. Such complex flows include turbulent flows past cylinders confined in a channel, interfacial flows of two immiscible fluids and flows driven by density stratifications. Two dimensional and three dimensional thermal lattice Boltzmann models have been developed to study non-linear dynamics of these flows. Detailed formulations of the single relaxation lattice Boltzmann method are presented. Also presented by the present author are several variations of the lattice Boltzmann method. These methods include the multi relaxation lattice Boltzmann, regularized lattice Boltzmann and thermal lattice Boltzmann. Multi relaxation time converts velocity space to moment space, and regularized lattice Boltzmann uses the non-equilibrium parts of the stress. These methods are introduced to overcome stability problem of the lattice Boltzmann method. A unique lattice Boltzmann model that combines regularized and multi-relaxation time lattice Boltzmann method is introduced here to overcome the shortcoming of the lattice Boltzmann method. It is demonstrated here that the new model is stable for high speed turbulent flows. Turbulent flow structures predicted by the proposed method agree well with those observed by the experiments and those predicted by the large eddy simulations. Spatial resolution of the turbulence resolved here is equivalent to that obtained by direct numerical simulations. A two dimensional nine velocity and a three dimensional fifteen velocity lattice Boltzmann models have been employed to study interfacial flows. Body forces and interactive forces are included in these models. Several different approaches are adopted to handle different type boundary conditions imposed on the velocity and temperature fields. The nonlinear stages of Rayleigh Taylor instabilities and droplets rising in a stagnant fluid are characterized. The developed model shows and more stable more accurate results. The thermal model was employed to study the Rayleigh-Benard convection in a square and rectangular cavity. It has been demonstrated here that the lattice Boltzmann method can be an effective computational fluid dynamics tool to tackle complex flows
Finite Volume Streaming-based Lattice Boltzmann algorithm for fluid-dynamics simulations: a one-to-one accuracy and performance study
A new finite volume (FV) discretisation method for the Lattice Boltzmann (LB)
equation which combines high accuracy with limited computational cost is
presented. In order to assess the performance of the FV method we carry out a
systematic comparison, focused on accuracy and computational performances, with
the standard (ST) Lattice Boltzmann equation algorithm. To our
knowledge such a systematic comparison has never been previously reported. In
particular we aim at clarifying whether and in which conditions the proposed
algorithm, and more generally any FV algorithm, can be taken as the method of
choice in fluid-dynamics LB simulations. For this reason the comparative
analysis is further extended to the case of realistic flows, in particular
thermally driven flows in turbulent conditions. We report the first successful
simulation of high-Rayleigh number convective flow performed by a Lattice
Boltzmann FV based algorithm with wall grid refinement.Comment: 15 pages, 14 figures (discussion changes, improved figure
readability
Fluctuating lattice Boltzmann
The lattice Boltzmann algorithm efficiently simulates the Navier Stokes
equation of isothermal fluid flow, but ignores thermal fluctuations of the
fluid, important in mesoscopic flows. We show how to adapt the algorithm to
include noise, satisfying a fluctuation-dissipation theorem (FDT) directly at
lattice level: this gives correct fluctuations for mass and momentum densities,
and for stresses, at all wavevectors . Unlike previous work, which recovers
FDT only as , our algorithm offers full statistical mechanical
consistency in mesoscale simulations of, e.g., fluctuating colloidal
hydrodynamics.Comment: 7 pages, 3 figures, to appear in Europhysics Letter
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.
Efficient kinetic method for fluid simulation beyond the Navier-Stokes equation
We present a further theoretical extension to the kinetic theory based
formulation of the lattice Boltzmann method of Shan et al (2006). In addition
to the higher order projection of the equilibrium distribution function and a
sufficiently accurate Gauss-Hermite quadrature in the original formulation, a
new regularization procedure is introduced in this paper. This procedure
ensures a consistent order of accuracy control over the non-equilibrium
contributions in the Galerkin sense. Using this formulation, we construct a
specific lattice Boltzmann model that accurately incorporates up to the third
order hydrodynamic moments. Numerical evidences demonstrate that the extended
model overcomes some major defects existed in the conventionally known lattice
Boltzmann models, so that fluid flows at finite Knudsen number (Kn) can be more
quantitatively simulated. Results from force-driven Poiseuille flow simulations
predict the Knudsen's minimum and the asymptotic behavior of flow flux at large
Kn
Lattice Boltzmann Approach to High-Speed Compressible Flows
We present an improved lattice Boltzmann model for high-speed compressible
flows. The model is composed of a discrete-velocity model by Kataoka and
Tsutahara [Phys. Rev. E \textbf{69}, 056702 (2004)] and an appropriate
finite-difference scheme combined with an additional dissipation term. With the
dissipation term parameters in the model can be flexibly chosen so that the von
Neumann stability condition is satisfied. The influence of the various model
parameters on the numerical stability is analyzed and some reference values of
parameter are suggested. The new scheme works for both subsonic and supersonic
flows with a Mach number up to 30 (or higher), which is validated by well-known
benchmark tests. Simulations on Riemann problems with very high ratios
() of pressure and density also show good accuracy and stability.
Successful recovering of regular and double Mach shock reflections shows the
potential application of the lattice Boltzmann model to fluid systems where
non-equilibrium processes are intrinsic. The new scheme for stability can be
easily extended to other lattice Boltzmann models.Comment: Figs.11 and 12 in JPEG format. Int. J. Mod. Phys. C (to appear
PENGARUH MODEL PEMBELAJARAN GENERATIF TERHADAP PENINGKATAN PEMAHAMAN KONSEP FISIKA \SISWA SMP NEGERI I7 KOTA BENGKULU
Multi-GPU implementations of the Lattice Boltzmann method are of practical interest as they allow the study of turbulent flows on large-scale simulations at high Reynolds numbers. Although programming GPUs, and in general power-efficient accelerators, typically guarantees high performances, the lack of portability in their low-level programming models implies significant efforts for maintainability and porting of applications. Directive-based models such as OpenACC look promising in tackling these aspects. In this work we will evaluate the performances of a Multi-GPU implementation of the Lattice Boltzmann method accelerated with OpenACC. The implementation will allow for multi-node simulations of fluid flows in complex geometries, also supporting heterogeneous clusters for which the load balancing problem is investigated
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