3,471 research outputs found

    Hermite regularization of the Lattice Boltzmann Method for open source computational aeroacoustics

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    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

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    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

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    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

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    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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