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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 196
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Book Description
Accurate and efficient turbulence simulation in complex geometries is a formidable chal-lenge. Traditional methods are often limited by low accuracy and/or restrictions to simplegeometries. We explore the merger of Discontinuous Galerkin (DG) spatial discretizationswith Variational Multi-Scale (VMS) modeling, termed Local VMS (LVMS), to overcomethese limitations. DG spatial discretizations support arbitrarily high-order accuracy on un-structured grids amenable for complex geometries. Furthermore, high-order, hierarchicalrepresentation within DG provides a natural framework fora prioriscale separation crucialfor VMS implementation. We show that the combined benefits of DG and VMS within theLVMS method leads to promising new approach to LES for use in complex geometries. The efficacy of LVMS for turbulence simulation is assessed by application to fully-developed turbulent channelflow. First, a detailed spatial resolution study is undertakento record the effects of the DG discretization on turbulence statistics. Here, the localhp refinement capabilites of DG are exploited to obtain reliable low-order statistics effi-ciently. Likewise, resolution guidelines for simulating wall-bounded turbulence using DGare established. We also explore the influence of enforcing Dirichlet boundary conditionsindirectly through numericalfluxes in DG which allows the solution to jump (slip) at thechannel walls. These jumps are effective in simulating the influence of the wall commen-surate with the local resolution and this feature of DG is effective in mitigating near-wallresolution requirements. In particular, we show that by locally modifying the numericalviscousflux used at the wall, we are able to regulate the near-wall slip through a penaltythat leads to improved shear-stress predictions. This work, demonstrates the potential ofthe numerical viscousflux to act as a numerically consistent wall-model and this successwarrents future research. As in any high-order numerical method some mechanism is required to control aliasingeffects due to nonlinear interactions and to ensure nonlinear stability of the method. Inthis context, we evaluate the merits of two approaches to de-aliasing -- spectralfilteringand polynomial dealiasing. While both approaches are successful, polynomial-dealiasingis found to be better suited for use in large-eddy simulation. Finally, results using LVMSare reported and show good agreement with reference direct numerical simulation therebydemonstrating the effectiveness of LVMS for wall-bounded turbulence. This success pavesthe way for future applications of LVMS to more complex turbulentflows. 3.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 196
Get Book Here
Book Description
Accurate and efficient turbulence simulation in complex geometries is a formidable chal-lenge. Traditional methods are often limited by low accuracy and/or restrictions to simplegeometries. We explore the merger of Discontinuous Galerkin (DG) spatial discretizationswith Variational Multi-Scale (VMS) modeling, termed Local VMS (LVMS), to overcomethese limitations. DG spatial discretizations support arbitrarily high-order accuracy on un-structured grids amenable for complex geometries. Furthermore, high-order, hierarchicalrepresentation within DG provides a natural framework fora prioriscale separation crucialfor VMS implementation. We show that the combined benefits of DG and VMS within theLVMS method leads to promising new approach to LES for use in complex geometries. The efficacy of LVMS for turbulence simulation is assessed by application to fully-developed turbulent channelflow. First, a detailed spatial resolution study is undertakento record the effects of the DG discretization on turbulence statistics. Here, the localhp refinement capabilites of DG are exploited to obtain reliable low-order statistics effi-ciently. Likewise, resolution guidelines for simulating wall-bounded turbulence using DGare established. We also explore the influence of enforcing Dirichlet boundary conditionsindirectly through numericalfluxes in DG which allows the solution to jump (slip) at thechannel walls. These jumps are effective in simulating the influence of the wall commen-surate with the local resolution and this feature of DG is effective in mitigating near-wallresolution requirements. In particular, we show that by locally modifying the numericalviscousflux used at the wall, we are able to regulate the near-wall slip through a penaltythat leads to improved shear-stress predictions. This work, demonstrates the potential ofthe numerical viscousflux to act as a numerically consistent wall-model and this successwarrents future research. As in any high-order numerical method some mechanism is required to control aliasingeffects due to nonlinear interactions and to ensure nonlinear stability of the method. Inthis context, we evaluate the merits of two approaches to de-aliasing -- spectralfilteringand polynomial dealiasing. While both approaches are successful, polynomial-dealiasingis found to be better suited for use in large-eddy simulation. Finally, results using LVMSare reported and show good agreement with reference direct numerical simulation therebydemonstrating the effectiveness of LVMS for wall-bounded turbulence. This success pavesthe way for future applications of LVMS to more complex turbulentflows. 3.
Author: Volker John
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: Songül Kaya Merdan
Publisher: LAP Lambert Academic Publishing
ISBN: 9783845432083
Category :
Languages : en
Pages : 80
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Book Description
Despite efforts of more than centuries, turbulence phenomena is categorized as an unsolved problem. Turbulence is part of everyday's life. The majority of flows of industrial and technological applications are turbulent; natural flows are invariably so. There are many important and interesting physical phenomena which are connected with turbulent flows. Turbulence is observed in natural and engineering applications such as in weather prediction, air pollution, water pollution, aerodynamics and heat exchangers. This work considers an accurate and reliable solutions of turbulent flows. It is concerned with one of the most promising approaches to the numerical simulation of turbulent flows, the subgrid eddy viscosity models. We analyze both continuous and discontinuous finite element approximation of the new subgrid eddy viscosity model. This approach has the advantage that the diffusivity is introduced only on the small scales of the flow. Numerical test shows the new stabilization technique is robust and efficient in solving Navier-Stokes equations for a wide range of Reynolds numbers.
Author: Lars Röhe
Publisher:
ISBN: 9783862471737
Category :
Languages : en
Pages : 205
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Book Description
Author: Pierre Sagaut
Publisher: World Scientific
ISBN: 1848169876
Category : Science
Languages : en
Pages : 446
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Book Description
The book aims to provide the reader with an updated general presentation of multiscale/multiresolution approaches in turbulent flow simulations. All modern approaches (LES, hybrid RANS/LES, DES, SAS) are discussed and recast in a global comprehensive framework. Both theoretical features and practical implementation details are addressed. Some full scale applications are described, to provide the reader with relevant guidelines to facilitate a future use of these methods.
Author: Elaine Cohen
Publisher: CRC Press
ISBN: 1439864209
Category : Computers
Languages : en
Pages : 638
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Book Description
Written by researchers who have helped found and shape the field, this book is a definitive introduction to geometric modeling. The authors present all of the necessary techniques for curve and surface representations in computer-aided modeling with a focus on how the techniques are used in design. They achieve a balance between mathematical rigor
Author: Naveed Ahmed
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Various realizations of variational multiscale (VMS) methods for simulating turbulent incompressible flows have been proposed in the past fifteen years. All of these realizations obey the basic principles of VMS methods: They are based on the variational formulation of the incompressible Navier-Stokes equations and the scale separation is defined by projections. However, apart from these common basic features, the various VMS methods look quite different. In this review, the derivation of the different VMS methods is presented in some detail and their relation among each other and also to other discretizations is discussed. Another emphasis consists in giving an overview about known results from the numerical analysis of the VMS methods. A few results are presented in detail to highlight the used mathematical tools. Furthermore, the literature presenting numerical studies with the VMS methods is surveyed and the obtained results are summarized.
Author: Farshad Navah
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
"This work discusses the development, the verification and the validation of high-order (of accuracy) solvers for the simulation of turbulent fluid flows. In a first part, a methodology for the verification of high-order solvers is proposed which examines the implementation, in a given computer software, of mathematical models that represent the flow dynamics. The method of manufactured solutions is adopted which allows for the exact evaluation of discretization errors and observed orders of accuracy. The latter are compared to the theoretical orders of accuracy for a variety of increasingly complex problems, starting from unbounded (by walls) inviscid flows and gradually reaching the case of realistic turbulent boundary layers, modelled by the Reynolds-averaged Navier-Stokes equations, along with the original and the negative Spalart-Allmaras closure models. Each case serves to illustrate and discuss salient aspects of the proposed methodology.Code verification via manufactured solutions is furthermore distinguished from solution verification and the latter is extended to high-order frameworks by describing the approach for error estimation via extrapolation of high-order solutions which is applied, as an example, to the case of turbulent flow over a flat plate. This exercise enabled the exploration into the question of high-order grid convergence for various output quantities of interest as well as the question of uncertainty analysis. This pointed at the inadequacy of substituting solution verification to proper high-order solver verification, even for a relatively simple problem and an expert set of grids. It is therefore recommended to use the solutions of actual problems for engineering and science applications, only along with estimated numerical uncertainties, especially for lower orders which are more error-prone. In the second part of this work, a compact high-order variational multiscale method for the large-eddy simulation of turbulence is devised and validated. The existing multiscale method is thus expanded from modal frameworks to a large family of compact high-order nodal schemes, represented by the recent flux reconstruction discretization method. The potential of the proposed formulation is then assessed on a Taylor-Green vortex problem and its results are validated against the filtered data from direct numerical simulations. It is thus revealed that proper de-aliasing is mandatory to conserve the quality of high-order large-eddy simulation. Furthermore, reducing the numerical dissipation of Roe's Riemann solver is found to contribute to improving low-Mach flow solutions for variational multiscale methods. Finally, the proposed variational-multiscale formulation resulted in noticeable improvements over the baseline implicit as well as the classical large-eddy simulations." --
Author: Naveed Ahmed
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: René de Borst
Publisher: Springer Science & Business Media
ISBN: 9048198097
Category : Computers
Languages : en
Pages : 451
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Book Description
This work gives a modern, up-to-date account of recent developments in computational multiscale mechanics. Both upscaling and concurrent computing methodologies will be addressed for a range of application areas in computational solid and fluid mechanics: Scale transitions in materials, turbulence in fluid-structure interaction problems, multiscale/multilevel optimization, multiscale poromechanics. A Dutch-German research group that consists of qualified and well-known researchers in the field has worked for six years on the topic of computational multiscale mechanics. This text provides a unique opportunity to consolidate and disseminate the knowledge gained in this project. The addition of chapters written by experts outside this working group provides a broad and multifaceted view of this rapidly evolving field.
