3,865 research outputs found
Lattice Boltzmann Approach to Viscous Flows Between Parallel Plates
Four different kinds of laminar flows between two parallel plates are
investigated using the Lattice Boltzmann Method (LBM). The LBM accuracy is
estimated in two cases using numerical fits of the parabolic velocity profiles
and the kinetic energy decay curves, respectively. The error relative to the
analytical kinematic viscosity values was found to be less than one percent in
both cases. The LBM results for the unsteady development of the flow when one
plate is brought suddenly at a constant velocity, are found in excellent
agreement with the analytical solution. Because the classical Schlichting's
approximate solution for the entrance--region flow is not valid for small
Reynolds numbers, a Finite Element Method solution was used in order to check
the accuracy of the LBM results
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
Hermite regularization of the Lattice Boltzmann Method for open source computational aeroacoustics
The lattice Boltzmann method (LBM) is emerging as a powerful engineering tool
for aeroacoustic computations. However, the LBM has been shown to present
accuracy and stability issues in the medium-low Mach number range, that is of
interest for aeroacoustic applications. Several solutions have been proposed
but often are too computationally expensive, do not retain the simplicity and
the advantages typical of the LBM, or are not described well enough to be
usable by the community due to proprietary software policies. We propose to use
an original regularized collision operator, based on the expansion in Hermite
polynomials, that greatly improves the accuracy and stability of the LBM
without altering significantly its algorithm. The regularized LBM can be easily
coupled with both non-reflective boundary conditions and a multi-level grid
strategy, essential ingredients for aeroacoustic simulations. Excellent
agreement was found between our approach and both experimental and numerical
data on two different benchmarks: the laminar, unsteady flow past a 2D cylinder
and the 3D turbulent jet. Finally, most of the aeroacoustic computations with
LBM have been done with commercial softwares, while here the entire theoretical
framework is implemented on top of an open source library (Palabos).Comment: 34 pages, 12 figures, The Journal of the Acoustical Society of
America (in press
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
Fractal model and Lattice Boltzmann Method for Characterization of Non-Darcy Flow in Rough Fractures.
The irregular morphology of single rock fracture significantly influences subsurface fluid flow and gives rise to a complex and unsteady flow state that typically cannot be appropriately described using simple laws. Yet the fluid flow in rough fractures of underground rock is poorly understood. Here we present a numerical method and experimental measurements to probe the effect of fracture roughness on the properties of fluid flow in fractured rock. We develop a series of fracture models with various degrees of roughness characterized by fractal dimensions that are based on the Weierstrass-Mandelbrot fractal function. The Lattice Boltzmann Method (LBM), a discrete numerical algorithm, is employed for characterizing the complex unsteady non-Darcy flow through the single rough fractures and validated by experimental observations under the same conditions. Comparison indicates that the LBM effectively characterizes the unsteady non-Darcy flow in single rough fractures. Our LBM model predicts experimental measurements of unsteady fluid flow through single rough fractures with great satisfactory, but significant deviation is obtained from the conventional cubic law, showing the superiority of LBM models of single rough fractures
Recommended from our members
Microchannel fluid flow and heat transfer by lattice boltzmann method
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Micro flow has become a popular field of interest due to the advent of micro electromechanical systems (MEMS). In this work, the lattice Boltzmann method, a particle-based approach, is applied to simulate the two-dimensional micro channel fluid flow.
We simulated fluid flow and heat transfer inside microchannel, the prototype application of this study is micro-heat exchangers. The main incentive to look at fluidic behaviour at micron scale is that micro devices tend to behave much differently from the objects we are used to handling in daily life. The choice of using LBM for micro flow simulation is a good one owing to the fact that it is based on the Boltzmann equation which is valid for the whole range of the Knudsen number. Slip velocity and temperature jump boundary conditions are used for the microchannel simulations with Knudsen number values covering the slip flow. The lattice Bhatnagar-Gross-Krook single relaxation time approximation was used. The results found are compared with the Navier-Stokes analytical and numerical results available in the literature and good matches are observed
- …