Design and Application of Discrete Explicit Filters for Large Eddy Simulation of Compressible Turbulent Flows PDF Download
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Author: Willem Deconinck
Publisher:
ISBN:
Category : Aerospace engineering
Languages : en
Pages : 0
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Author: Willem Deconinck
Publisher:
ISBN:
Category : Aerospace engineering
Languages : en
Pages : 0
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Author: Deconinck Willem
Publisher: LAP Lambert Academic Publishing
ISBN: 9783659529887
Category : Technology & Engineering
Languages : en
Pages : 0
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Book Description
In the context of Large Eddy Simulation (LES) of turbulent flows, there is a current need to compare and evaluate different proposed subfilter-scale models in order to assess their suitability for various applications. In order to carefully compare subfilter-scale models and compare LES predictions to Direct Numerical Simulation (DNS) results (the latter would be helpful in the comparison and validation of models), there is a real need for a "grid-independent" LES capability and explicit filtering methods offer one means by which this may be achieved. Advantages of explicit filtering are that it provides a means for eliminating aliasing errors, allows for the direct control of commutation errors, and most importantly allows a decoupling between the mesh spacing and the filter width which is the primary reason why there are difficulties in comparing LES solutions obtained on different grids. This book considers the design and assessment of discrete explicit filters and their application to isotropic turbulence prediction. This book was submitted for the degree of Masters of Applied Science at the Graduate Department of Aerospace Engineering at the University of Toronto.
Author: Eric Garnier
Publisher: Springer
ISBN: 9789048128181
Category : Science
Languages : en
Pages : 276
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Book Description
This book addresses both the fundamentals and the practical industrial applications of Large Eddy Simulation (LES) in order to bridge the gap between LES research and the growing need to use it in engineering modeling.
Author: Luigi Carlo Berselli
Publisher: Springer Science & Business Media
ISBN: 9783540263166
Category : Computers
Languages : en
Pages : 378
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Book Description
The LES-method is rapidly developing in many practical applications in engineering The mathematical background is presented here for the first time in book form by one of the leaders in the field
Author: Sanjeeb T. Bose
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The governing equations for large-eddy simulation (LES) are derived from the application of a low-pass filter to the Navier-Stokes equations. LES has shown to be a tractable method for the computation of high Reynolds number turbulent flows, primarily because the filtration of the Navier-Stokes equations removes the small scales of motion that would otherwise impose prohibitive resolution requirements. The effect of the scales of motion that are smaller than the filter width on the large, resolved scales are then modeled. In practice, the filter used to derive the LES governing equation is not formally defined and instead, it is assumed that the discretization of LES equation will implicitly act as a low-pass filter. This study investigates an alternative derivation of the LES governing equations that requires the formal definition of the filtration operator, known as explicitly filtered LES. It is shown that decoupling the filtering operation from the underlying grid allows for the isolation of subgrid-scale (SGS) modeling errors from numerical discretization errors. In this grid-independent context, it is demonstrated that standard eddy viscosity models are inaccurate at coarse resolutions. By leveraging the definition of the filtering operator, an SGS model is subsequently derived from a low order perturbation of the explicitly filtered governing equations. LES of canonical wall bounded flows (e.g., channels and ducts) at coarse resolutions validate the improved accuracy of the proposed SGS model. Simulations of practical engineering configurations require the ability to handle complex geometries. Previous explicitly filtered LES calculations have been limited to structured grid discretizations because of the difficulty in constructing a low-pass filter on unstructured grids. The explicitly filtered framework and the proposed SGS model are extended for use in unstructured grid environments through the use of differential filters. Unstructured grids also provide the ability to locally increase resolution in regions of the flow where the SGS model is unable to accurately model the stress provided by the unresolved scales of motion. A novel adaptation technique is suggested where the mesh (and/or filter) is refined in regions of the flow where estimates of the SGS fluctuations are largest. An LES of a three-dimensional stalled diffuser is performed to demonstrate the efficacy of the SGS model based mesh refinement criteria and the capabilities of the differential filters on unstructured grids. Lastly, a dynamic wall boundary condition is derived from the differential filter for wall-modeled large-eddy simulation where the near wall turbulence is not resolved. This differential filter based wall model successfully predicts mean dynamics of both wall-bounded flows (channels) and separating flows in complex geometries (airfoil at near-stall conditions) without the prescription of any ad hoc coefficients or RANS/LES hybridization.
Author: Alvaro A. Aldama
Publisher: Springer Science & Business Media
ISBN: 3642840914
Category : Science
Languages : en
Pages : 410
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Book Description
1. 1 Scope of the Study The detailed and reasonably accurate computation of large scale turbulent flows has become increasingly important in geophysical and engi neering applications in recent years. The definition of water quality management policies for reservoirs, lakes, estuaries, and coastal waters, as well as the design of cooling ponds and solar ponds, requires an ade quate quantitative description of turbulent flows. When the diffusion of some tracer (be it active, such as temperature or salinity, or passive, such as dissolved oxygen) is of relevance to a specific application, the proper determination of the effects of turbulent transport processes has paramount importance. Thus, for instance, the proper understanding of lake and reservoir dynamics requires, as a first step, the ability to simulate turbulent flows. Applications in other areas of geophysical research, such as meteorology and oceanography are easily identified and large in number. It should be stressed that, in this context, the analyst seeks predictive ability to a certain extent. Accordingly, the need for simulation models that closely resemble the natural processes to be repre sented has recently become more evident. Since the late 1960s considerable effort has been devoted to the development of models for the simulation of complex turbulent flows. This has resulted in the establishment of two approaches which have been, or 2 have the potential for being, applied to problems of engineering and geophysical interest.
Author: Matthew J. Brazell
Publisher:
ISBN: 9781339441535
Category : Eddies
Languages : en
Pages : 85
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Book Description
The discontinuous Galerkin (DG) method is a formulation of the finite element method (FEM). DG provides the ability for a high order of accuracy in complex geometries, and allows for highly efficient parallelization algorithms. These attributes make the DG method attractive for solving the Navier-Stokes equations for large eddy simulation (LES). The main goal of this work is to investigate the feasibility of adopting an explicit filter in the numerical solution of the Navier-Stokes equations with DG. Explicit filtering has been shown to increase the numerical stability of under-resolved simulations and is needed for LES with dynamic sub-grid scale (SGS) models. The explicit filter takes advantage of DG’s framework where the solution is approximated using a polyno- mial basis where the higher modes of the solution correspond to a higher order polynomial basis. By removing high order modes, the filtered solution contains low order frequency content much like an explicit low pass filter. The explicit filter implementation is tested on a simple 1-D solver with an initial condi- tion that has some similarity to turbulent flows. The explicit filter does restrict the resolution as well as remove accumulated energy in the higher modes from aliasing. However, the ex- plicit filter is unable to remove numerical errors causing numerical dissipation. A second test case solves the 3-D Navier-Stokes equations of the Taylor-Green vortex flow (TGV). The TGV is useful for SGS model testing because it is initially laminar and transitions into a fully turbulent flow. The SGS models investigated include the constant coefficient Smagorinsky model, dynamic Smagorinsky model, and dynamic Heinz model. The constant coefficient Smagorinsky model is over dissipative, this is generally not desirable however it does add stability. The dynamic Smagorinsky model generally performs better, especially during the laminar-turbulent transition region as expected. The dynamic Heinz model which is based on an improved model, handles the laminar-turbulent transition region well while also showing additional robustness.
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781721608942
Category :
Languages : en
Pages : 26
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In this paper, turbulence-closure models are evaluated using the 'true' LES approach in turbulent channel flow. The study is an extension of the work presented by Gullbrand (2001), where fourth-order commutative filter functions are applied in three dimensions in a fourth-order finite-difference code. The true LES solution is the grid-independent solution to the filtered governing equations. The solution is obtained by keeping the filter width constant while the computational grid is refined. As the grid is refined, the solution converges towards the true LES solution. The true LES solution will depend on the filter width used, but will be independent of the grid resolution. In traditional LES, because the filter is implicit and directly connected to the grid spacing, the solution converges towards a direct numerical simulation (DNS) as the grid is refined, and not towards the solution of the filtered Navier-Stokes equations. The effect of turbulence-closure models is therefore difficult to determine in traditional LES because, as the grid is refined, more turbulence length scales are resolved and less influence from the models is expected. In contrast, in the true LES formulation, the explicit filter eliminates all scales that are smaller than the filter cutoff, regardless of the grid resolution. This ensures that the resolved length-scales do not vary as the grid resolution is changed. In true LES, the cell size must be smaller than or equal to the cutoff length scale of the filter function. The turbulence-closure models investigated are the dynamic Smagorinsky model (DSM), the dynamic mixed model (DMM), and the dynamic reconstruction model (DRM). These turbulence models were previously studied using two-dimensional explicit filtering in turbulent channel flow by Gullbrand & Chow (2002). The DSM by Germano et al. (1991) is used as the USFS model in all the simulations. This enables evaluation of different reconstruction models for the RSFS stresses. The DMM co
Author: Institute for Computer Applications in Science and Engineering
Publisher:
ISBN:
Category :
Languages : en
Pages : 52
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Book Description
Author: G. Erlebacher
Publisher:
ISBN:
Category :
Languages : en
Pages : 44
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