[PDF] Comparison Of High Order And Low Order Methods For Large Eddy Simulation Of A Compressible Shear Layer eBook

Author : National Aeronautics and Space Administration (NASA)
Publisher : Createspace Independent Publishing Platform
Page : 30 pages
File Size : 31,44 MB
Release : 2018-05-22
Category :
ISBN : 9781719402545

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The objective of this work is to compare a high-order solver with a low-order solver for performing Large-Eddy Simulations (LES) of a compressible mixing layer. The high-order method is the Wave-Resolving LES (WRLES) solver employing a Dispersion Relation Preserving (DRP) scheme. The low-order solver is the Wind-US code, which employs the second-order Roe Physical scheme. Both solvers are used to perform LES of the turbulent mixing between two supersonic streams at a convective Mach number of 0.46. The high-order and low-order methods are evaluated at two different levels of grid resolution. For a fine grid resolution, the low-order method produces a very similar solution to the highorder method. At this fine resolution the effects of numerical scheme, subgrid scale modeling, and filtering were found to be negligible. Both methods predict turbulent stresses that are in reasonable agreement with experimental data. However, when the grid resolution is coarsened, the difference between the two solvers becomes apparent. The low-order method deviates from experimental results when the resolution is no longer adequate. The high-order DRP solution shows minimal grid dependence. The effects of subgrid scale modeling and spatial filtering were found to be negligible at both resolutions. For the high-order solver on the fine mesh, a parametric study of the spanwise width was conducted to determine its effect on solution accuracy. An insufficient spanwise width was found to impose an artificial spanwise mode and limit the resolved spanwise modes. We estimate that the spanwise depth needs to be 2.5 times larger than the largest coherent structures to capture the largest spanwise mode and accurately predict turbulent mixing. Mankbadi, Mina R. and Georgiadis, Nicholas J. and DeBonis, James R. Glenn Research Center COMPUTATIONAL FLUID DYNAMICS; LARGE EDDY SIMULATION; TURBULENT MIXING; SHEAR LAYERS; COMPRESSIBLE BOUNDARY LAYER; BOUNDARY CONDITIONS; MATHEMATICAL MODELS; COMPUTATIONAL GRIDS

Author : Eric Garnier
Publisher : Springer Science & Business Media
Page : 280 pages
File Size : 10,86 MB
Release : 2009-08-11
Category : Science
ISBN : 9048128196

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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 : Peter R. Voke
Publisher : Springer Science & Business Media
Page : 438 pages
File Size : 25,40 MB
Release : 2012-12-06
Category : Technology & Engineering
ISBN : 940111000X

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It is a truism that turbulence is an unsolved problem, whether in scientific, engin eering or geophysical terms. It is strange that this remains largely the case even though we now know how to solve directly, with the help of sufficiently large and powerful computers, accurate approximations to the equations that govern tur bulent flows. The problem lies not with our numerical approximations but with the size of the computational task and the complexity of the solutions we gen erate, which match the complexity of real turbulence precisely in so far as the computations mimic the real flows. The fact that we can now solve some turbu lence in this limited sense is nevertheless an enormous step towards the goal of full understanding. Direct and large-eddy simulations are these numerical solutions of turbulence. They reproduce with remarkable fidelity the statistical, structural and dynamical properties of physical turbulent and transitional flows, though since the simula tions are necessarily time-dependent and three-dimensional they demand the most advanced computer resources at our disposal. The numerical techniques vary from accurate spectral methods and high-order finite differences to simple finite-volume algorithms derived on the principle of embedding fundamental conservation prop erties in the numerical operations. Genuine direct simulations resolve all the fluid motions fully, and require the highest practical accuracy in their numerical and temporal discretisation. Such simulations have the virtue of great fidelity when carried out carefully, and repre sent a most powerful tool for investigating the processes of transition to turbulence.

Author : Chaoqun Liu
Publisher : Bentham Science Publishers
Page : 321 pages
File Size : 26,84 MB
Release : 2017-12-08
Category : Technology & Engineering
ISBN : 1681085976

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This volume presents an implicitly implemented large eddy simulation (ILES) by using the fifth order bandwidth-optimized WENO scheme. The chosen method is applied to make comprehensive studies on ramp flows with and without control at Mach 2.5 and Re=5760. Flow control in the form of microramp vortex generators (MVG) is applied. The results show that a MVG can distinctly reduce the separation zone at the ramp corner and lower the boundary layer shape factor under simulated conditions. A series of new findings about the MVG-ramp flow are obtained, including structures relevant to surface pressure, three-dimensional structures of the re-compression shock waves, a complete surface separation pattern, momentum deficit and a new secondary vortex system. A new mechanism of shock-boundary layer interaction control by MVG associated with a series of vortex rings is also presented. Vortex rings strongly interact with air flow and play an important role in the separation zone reduction. Additionally, readers will learn about the governing equation, boundary condition, high quality grid generation, high order shock capturing scheme and DNS inflow condition in detail. This volume will, therefore, serve as a useful reference for aerospace researchers using LES methods to study shock boundary layer interaction and supersonic flow control.

Author : Maria Vittoria Salvetti
Publisher : Springer
Page : 608 pages
File Size : 25,89 MB
Release : 2019-02-02
Category : Technology & Engineering
ISBN : 3030049159

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This book gathers the proceedings of the 11th workshop on Direct and Large Eddy Simulation (DLES), which was held in Pisa, Italy in May 2017. The event focused on modern techniques for simulating turbulent flows based on the partial or full resolution of the instantaneous turbulent flow structures, as Direct Numerical Simulation (DNS), Large-Eddy Simulation (LES) or hybrid models based on a combination of LES and RANS approaches. In light of the growing capacities of modern computers, these approaches have been gaining more and more interest over the years and will undoubtedly be developed and applied further. The workshop offered a unique opportunity to establish a state-of-the-art of DNS, LES and related techniques for the computation and modeling of turbulent and transitional flows and to discuss about recent advances and applications. This volume contains most of the contributed papers, which were submitted and further reviewed for publication. They cover advances in computational techniques, SGS modeling, boundary conditions, post-processing and data analysis, and applications in several fields, namely multiphase and reactive flows, convection and heat transfer, compressible flows, aerodynamics of airfoils and wings, bluff-body and separated flows, internal flows and wall turbulence and other complex flows.

Author : Steven Randall Brill
Publisher :
Page : 0 pages
File Size : 14,33 MB
Release : 2022
Category :
ISBN :

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Turbulent flows occur in a wide variety of engineering applications from flow around an aircraft to internal combustion engines. However for most applications, the computational cost of a direct numerical simulation (DNS) is prohibitive because of the large range of scales of motion. Large eddy simulation (LES) is a more cost effective method where only the large scales of motion are resolved and the smaller scales are modeled. High-order methods, such as the spectral element method (SEM) and the discontinuous Galerkin method (DG), are well suited LES applications because their dissipation and dispersion properties. One limitation of high-order methods is that their polynomial basis cause unphysical oscillations when high-gradient features are under-resolved. For wall-bounded flows, even LES is too expensive for most applications because a large number of elements are needed near the wall to resolve the boundary layer. Wall-modeled LES (WMLES) addresses this challenge by modeling the near wall region while using an LES level of accuracy away from the wall. Traditionally, wall-models use an analytical model to compute the a modeled shear stress on the wall and enforce it as a boundary condition. While shear stress wall-models have shown success, they creates an unphysical solution in the near-wall region. Additionally, these methods are primarily designed for low-order methods and have not been integrated with the advantages of high-order methods. In this thesis, I discuss the development of a solution enrichment method for the spectral element method that augments the polynomial solution with a problem specific non-polynomial enrichment function. This method enhances the ability of SEM to model the targeted feature without unphysical oscillations. The framework is designed to be easily implemented in existing solvers to make it more easily usable for industrial applications and the method is implemented in the open-source solver Nek5000. The enrichment framework is then used to develop a turbulent wall-model for WMLES that maintains a physical solution and turbulent fluctuations throughout the domain. The wall-model enriches the polynomial solution representation with a law-of-the-wall enrichment function so that the large gradients in the near-wall region can be captured with large elements without oscillations. In comparison to traditional shear stress wall-models, the enrichment wall-model is able to better capture the mean velocity profile with larger elements.

Author : D. Drikakis
Publisher : Springer Science & Business Media
Page : 390 pages
File Size : 42,50 MB
Release : 2006-04-11
Category : Science
ISBN : 0306484218

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In various branches of fluid mechanics, our understanding is inhibited by the presence of turbulence. Although many experimental and theoretical studies have significantly helped to increase our physical understanding, a comp- hensive and predictive theory of turbulent flows has not yet been established. Therefore, the prediction of turbulent flow relies heavily on simulation stra- gies. The development of reliable methods for turbulent flow computation will have a significant impact on a variety of technological advancements. These range from aircraft and car design, to turbomachinery, combustors, and process engineering. Moreover, simulation approaches are important in materials - sign, prediction of biologically relevant flows, and also significantly contribute to the understanding of environmental processes including weather and climate forecasting. The material that is compiled in this book presents a coherent account of contemporary computational approaches for turbulent flows. It aims to p- vide the reader with information about the current state of the art as well as to stimulate directions for future research and development. The book puts part- ular emphasis on computational methods for incompressible and compressible turbulent flows as well as on methods for analysing and quantifying nume- cal errors in turbulent flow computations. In addition, it presents turbulence modelling approaches in the context of large eddy simulation, and unfolds the challenges in the field of simulations for multiphase flows and computational fluid dynamics (CFD) of engineering flows in complex geometries. Apart from reviewing main research developments, new material is also included in many of the chapters.

Author : Francesco Capuano
Publisher : Youcanprint
Page : 96 pages
File Size : 15,76 MB
Release : 2019-12-27
Category : Mathematics
ISBN : 8891196975

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La tesi di dottorato è incentrata sullo sviluppo di strumenti e metodologie avanzate per la simulazione numerica di flussi turbolenti con tecniche Large-Eddy Simulation (LES) e Direct Numerical Simulation (DNS). In particolare, si propone una metodologia di avanzamento temporale innovativa di tipo Runge-Kutta(RK) capace di riprodurre le prestazioni di robustezza dei metodi skew-symmetric classici con maggiore efficienza computazionale. La rigorosa trattazione teorica sviluppata nel lavoro ha permesso di ricavare nuovi schemi RK con un determinato ordine di accuratezza sulla soluzione e sulla conservazione di energia discreta. La tecnica ha mostrato di essere più efficiente degli schemi classici, fornendo, a parità di risultati, tempi di calcolo inferiori fino al 50%.