3,471 research outputs found
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
Field Scale Reservoir Simulation through a Lattice Boltzmann Framework
The primary motivation of this work is to simulate the complex behavior of oil,
gas and water as it flows through an unconventional reservoir. Unconventional reservoirs require hydraulic fracturing to provide the reservoir with conductive pathways for fluid to flow. Without fracturing the rock, the oil and gas would remain trapped in impermeable pore spaces. Unconventional reservoirs typically exhibit high heterogeneity in rock properties but also in fluid flow regimes. A simulation tool needs to be able to capture small scale rock heterogeneities, multiple flow regimes, and additional interaction physics between the rock and fluid.
In this dissertation, an alternative approach to modeling oil and gas reservoirs
at the field scale is presented. Instead of a “top down” paradigm, typical of classic reservoir simulation techniques (finite element, finite volume and finite difference methods), this work focuses on a “bottom up” paradigm called the lattice Boltzmann method (LBM).
The LBM is a numerical discretization of the Boltzmann equation, in which a
fluid is described as a distribution of particles, each with a unique velocity. The
evolution of the distribution of particles is governed by a series of streaming and collision operations. The streaming operation translates the particle distribution through space. The collision operator describes how the particle distribution interacts with other distributions -- through collision and a transfer of momentum. The collective behavior of small scale particle dynamics (streaming and collision steps) yield macroscopic fluid behavior in the large space and time scale limit
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
A Non-uniform Staggered Cartesian Grid approach for Lattice-Boltzmann method
We propose a numerical approach based on the Lattice-Boltzmann method (LBM) for dealing with mesh refinement of Non-uniform Staggered Cartesian Grid. We explain, in detail, the strategy for mapping LBM over such geometries. The main benefit of this approach, compared to others, consists of solving all fluid units only once per time-step, and also reducing considerably the complexity of the communication and memory management between different refined levels. Also, it exhibits a better matching for parallel processors. To validate our method, we analyze several standard test scenarios, reaching satisfactory results with respect to other stateof-the-art methods. The performance evaluation proves that our approach not only exhibits a simpler and efficient scheme for dealing with mesh refinement, but also fast resolution, even in those scenarios where our approach needs to use a higher number of fluid units
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