2,154 research outputs found
Automatic grid refinement criterion for lattice Boltzmann method
In all kinds of engineering problems, and in particular in methods for
computational fluid dynamics based on regular grids, local grid refinement is
of crucial importance. To save on computational expense, many applications
require to resolve a wide range of scales present in a numerical simulation by
locally adding more mesh points. In general, the need for a higher (or a lower)
resolution is not known a priori, and it is therefore difficult to locate areas
for which local grid refinement is required. In this paper, we propose a novel
algorithm for the lattice Boltzmann method, based on physical concepts, to
automatically construct a pattern of local refinement. We apply the idea to the
two-dimensional lid-driven cavity and show that the automatically refined grid
can lead to results of equal quality with less grid points, thus sparing
computational resources and time. The proposed automatic grid refinement
strategy has been implemented in the parallel open-source library Palabos
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
SBoTFlow: A Scalable framework using lattice Boltzmann method and Topology-confined mesh refinement for moving-body applications
This paper proposes a scalable lattice-Boltzmann computational framework
(SBoTFlow) for simulations of flexible moving objects in an incompressible
fluid flow. Behavior of fluid flow formed from moving boundaries of
flexible-object motions is obtained through the multidirect forcing immersed
boundary scheme associated with the lattice Boltzmann equation with a parallel
topology-confined block refinement framework. We first demonstrate that the
hydrodynamic quantities computed in this manner for standard benchmarks,
including the Tayler-Green vortex flow and flow over an obstacle-embedded
lid-driven cavity and an isolated circular cylinder, agree well with those
previously published in the literature. We then exploit the framework to probe
the underlying dynamic properties contributing to fluid flow under flexible
motions at different Reynolds numbers by simulating large-scale flapping wing
motions of both amplitude and frequency. The analysis shows that the proposed
numerical framework for pitching and flapping motions has a strong ability to
accurately capture high amplitudes, specifically up to , and a
frequency of . This suggests that the present parallel numerical
framework has the potential to be used in studying flexible motions, such as
insect flight or wing aerodynamics
A Lifting Relation from Macroscopic Variables to Mesoscopic Variables in Lattice Boltzmann Method: Derivation, Numerical Assessments and Coupling Computations Validation
In this paper, analytic relations between the macroscopic variables and the
mesoscopic variables are derived for lattice Boltzmann methods (LBM). The
analytic relations are achieved by two different methods for the exchange from
velocity fields of finite-type methods to the single particle distribution
functions of LBM. The numerical errors of reconstructing the single particle
distribution functions and the non-equilibrium distribution function by
macroscopic fields are investigated. Results show that their accuracy is better
than the existing ones. The proposed reconstruction operator has been used to
implement the coupling computations of LBM and macro-numerical methods of FVM.
The lid-driven cavity flow is chosen to carry out the coupling computations
based on the numerical strategies of domain decomposition methods (DDM). The
numerical results show that the proposed lifting relations are accurate and
robust
Dynamic density functional theory versus Kinetic theory of simple fluids
By combining methods of kinetic and density functional theory, we present a
description of molecular fluids which accounts for their microscopic structure
and thermodynamic properties as well as for the hydrodynamic behavior. We focus
on the evolution of the one particle phase space distribution, rather than on
the evolution of the average particle density, which features in dynamic
density functional theory. The resulting equation can be studied in two
different physical limits: diffusive dynamics, typical of colloidal fluids
without hydrodynamic interaction, where particles are subject to overdamped
motion resulting from the coupling with a solvent at rest, and inertial
dynamics, typical of molecular fluids. Finally, we propose an algorithm to
solve numerically and efficiently the resulting kinetic equation by employing a
discretization procedure analogous to the one used in the Lattice Boltzmann
method.Comment: 15 page
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