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Author: Celestin P. Zemtsop Publisher: ISBN: 9781303050381 Category : Eddies Languages : en Pages : 115
Book Description
Swirl flows are useful in many engineering and environmental applications. They can be utilized to reduce emissions of pollutants, to improve ignition stability, and to stabilize a flame for clean combustion. The majority of swirl flows include both wall-bounded regions and free shear flow regions. Experimental research cannot provide all the information needed for the study of these flows. Numerical simulations of swirl flows provide more insights into the structure of the swirl flows. The direct numerical simulation (DNS) method is an accurate and reliable tool for flow simulations but computationally expensive. Reynolds-averaged Navier-Stokes (RANS) methods are computationally less expensive for the simulation of wall-bounded and free shear flows, but they turn out to be not well appropriate for turbulent swirling jet simulations. Large-eddy simulation (LES) is an appropriate modeling approach for turbulent swirl flow simulations, but the calculation of the free swirling jet using LES needs fluctuating inlet velocity conditions. The generation of such fluctuating velocity fields could be done by performing a LES of the nozzle flow. Unfortunately, the computational costs of such LES are comparable to those of DNS. A need thus arises to apply a hybrid RANS/LES method that combines two main advantages, the capability of LES methods in capturing instantaneous flow structures and the low computational costs of RANS methods. In this study, the performance of two hybrid approaches, a segregated RANS/LES method, and a unified RANS/LES method, is investigated regarding the simulation of turbulent swirling jet flows. The segregated model combines a RANS model in the nozzle region and a LES model in the jet region, whereas the unified model combines a RANS model in near-wall regions with a LES model away from the wall. This study provides evidence that the unified turbulence model is a better tool to predict swirl flows and, more importantly, a better tool to calculate the vortex breakdown. The accuracy of the numerical predictions is confirmed by comparing available experimental data for non-swirling and swirling jet flows with computational results. The validated model is used to study the mechanism of swirl effects, vortex breakdown, and scalar mixing.
Author: Celestin P. Zemtsop Publisher: ISBN: 9781303050381 Category : Eddies Languages : en Pages : 115
Book Description
Swirl flows are useful in many engineering and environmental applications. They can be utilized to reduce emissions of pollutants, to improve ignition stability, and to stabilize a flame for clean combustion. The majority of swirl flows include both wall-bounded regions and free shear flow regions. Experimental research cannot provide all the information needed for the study of these flows. Numerical simulations of swirl flows provide more insights into the structure of the swirl flows. The direct numerical simulation (DNS) method is an accurate and reliable tool for flow simulations but computationally expensive. Reynolds-averaged Navier-Stokes (RANS) methods are computationally less expensive for the simulation of wall-bounded and free shear flows, but they turn out to be not well appropriate for turbulent swirling jet simulations. Large-eddy simulation (LES) is an appropriate modeling approach for turbulent swirl flow simulations, but the calculation of the free swirling jet using LES needs fluctuating inlet velocity conditions. The generation of such fluctuating velocity fields could be done by performing a LES of the nozzle flow. Unfortunately, the computational costs of such LES are comparable to those of DNS. A need thus arises to apply a hybrid RANS/LES method that combines two main advantages, the capability of LES methods in capturing instantaneous flow structures and the low computational costs of RANS methods. In this study, the performance of two hybrid approaches, a segregated RANS/LES method, and a unified RANS/LES method, is investigated regarding the simulation of turbulent swirling jet flows. The segregated model combines a RANS model in the nozzle region and a LES model in the jet region, whereas the unified model combines a RANS model in near-wall regions with a LES model away from the wall. This study provides evidence that the unified turbulence model is a better tool to predict swirl flows and, more importantly, a better tool to calculate the vortex breakdown. The accuracy of the numerical predictions is confirmed by comparing available experimental data for non-swirling and swirling jet flows with computational results. The validated model is used to study the mechanism of swirl effects, vortex breakdown, and scalar mixing.
Author: Sharath Girimaji Publisher: Springer ISBN: 331915141X Category : Technology & Engineering Languages : en Pages : 481
Book Description
This book gathers the proceedings of the Fifth Symposium on Hybrid RANS-LES Methods, which was held on March 19-21 in College Station, Texas, USA. The different chapters, written by leading experts, reports on the most recent developments in flow physics modelling, and gives a special emphasis to industrially relevant applications of hybrid RANS-LES methods and other turbulence-resolving modelling approaches. The book addresses academic researchers, graduate students, industrial engineers, as well as industrial R&D managers and consultants dealing with turbulence modelling, simulation and measurement, and with multidisciplinary applications of computational fluid dynamics (CFD), such as flow control, aero-acoustics, aero-elasticity and CFD-based multidisciplinary optimization. It discusses in particular advanced hybrid RANS-LES methods. Further topics include wall-modelled Large Eddy Simulation (WMLES) methods, embedded LES, and a comparison of the LES methods with both hybrid RANS-LES and URANS methods. Overall, the book provides readers with a snapshot on the state-of-the-art in CFD and turbulence modelling, with a special focus to hybrid RANS-LES methods and their industrial applications.
Author: Jonathan Wayne Naughton Publisher: ISBN: Category : Eddies Languages : en Pages : 30
Book Description
Swirling jet flows have been studied experimentally and computationally and the results have been compared with theory. Three-component Laser Doppler Anemometry (LDA) measurements have been carried out for swirling jets of various strengths and swirl distributions. Radial profiles of velocity have been obtained from the jet exit to 50 diameters downstream. The experimental results are consistent with previous results and with similarity theory for weakly swirling turbulent jets. However, the parametric range and spatial domain of the current data set makes it suitable for validation. Computational simulations have also been performed using a combination of Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) approaches. The results have been validated with experimental data and used to explore the mechanisms behind the increased mixing enhancement observed. The combined experimental/computational effort is still ongoing, but the experiences to date have demonstrated the effectiveness of such an approach.
Author: Pierre Sagaut Publisher: World Scientific ISBN: 1908979879 Category : Science Languages : en Pages : 356
Book Description
This unique book gives a general unified presentation of the use of the multiscale/multiresolution approaches in the field of turbulence. The coverage ranges from statistical models developed for engineering purposes to multiresolution algorithms for the direct computation of turbulence. It provides the only available up-to-date reviews dealing with the latest and most advanced turbulence models (including LES, VLES, hybrid RANS/LES, DES) and numerical strategies.The book aims at providing the reader with a comprehensive description of modern strategies for turbulent flow simulation, ranging from turbulence modeling to the most advanced multilevel numerical methods./a
Author: Paul Durbin Publisher: Elsevier ISBN: 0128208902 Category : Technology & Engineering Languages : en Pages : 554
Book Description
Advanced Approaches in Turbulence: Theory, Modeling, Simulation and Data Analysis for Turbulent Flows focuses on the updated theory, simulation and data analysis of turbulence dealing mainly with turbulence modeling instead of the physics of turbulence. Beginning with the basics of turbulence, the book discusses closure modeling, direct simulation, large eddy simulation and hybrid simulation. The book also covers the entire spectrum of turbulence models for both single-phase and multi-phase flows, as well as turbulence in compressible flow. Turbulence modeling is very extensive and continuously updated with new achievements and improvements of the models. Modern advances in computer speed offer the potential for elaborate numerical analysis of turbulent fluid flow while advances in instrumentation are creating large amounts of data. This book covers these topics in great detail. Covers the fundamentals of turbulence updated with recent developments Focuses on hybrid methods such as DES and wall-modeled LES Gives an updated treatment of numerical simulation and data analysis
Author: Pierre Sagaut Publisher: World Scientific ISBN: 1848169884 Category : Mathematics Languages : en Pages : 446
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./a
Author: National Aeronautics and Space Administration (NASA) Publisher: Createspace Independent Publishing Platform ISBN: 9781722646417 Category : Languages : en Pages : 56
Book Description
Aircraft engine combustors generally involve turbulent swirling flows in order to enhance fuel-air mixing and flame stabilization. It has long been recognized that eddy viscosity turbulence models are unable to appropriately model swirling flows. Therefore, it has been suggested that, for the modeling of these flows, a second order closure scheme should be considered because of its ability in the modeling of rotational and curvature effects. However, this scheme will require solution of many complicated second moment transport equations (six Reynolds stresses plus other scalar fluxes and variances), which is a difficult task for any CFD implementations. Also, this scheme will require a large amount of computer resources for a general combustor swirling flow. This report is devoted to the development of a cubic Reynolds stress-strain model for turbulent swirling flows, and was inspired by the work of Launder's group at UMIST. Using this type of model, one only needs to solve two turbulence equations, one for the turbulent kinetic energy k and the other for the dissipation rate epsilon. The cubic model developed in this report is based on a general Reynolds stress-strain relationship. Two flows have been chosen for model evaluation. One is a fully developed rotating pipe flow, and the other is a more complex flow with swirl and recirculation. Shih, Tsan-Hsing and Zhu, Jiang and Liou, William and Chen, Kuo-Huey and Liu, Nan-Suey and Lumley, John L. Glenn Research Center...
Author: Christophe Brun Publisher: Springer ISBN: 9783642100673 Category : Technology & Engineering Languages : en Pages : 0
Book Description
Large Eddy Simulation (LES) is a high-fidelity approach to the numerical simulation of turbulent flows. Recent developments have shown LES to be able to predict aerodynamic noise generation and propagation as well as the turbulent flow, by means of either a hybrid or a direct approach. This book is based on the results of two French/German research groups working on LES simulations in complex geometries and noise generation in turbulent flows. The results provide insights into modern prediction approaches for turbulent flows and noise generation mechanisms as well as their use for novel noise reduction concepts.
Author: Celestin P. Zemtsop
Author: Celestin P. Zemtsop
Author: Sharath Girimaji
Author: Jonathan Wayne Naughton
Author: Keivan Khademi Shamami
Author: Pierre Sagaut
Author: Paul Durbin
Author: Pierre Sagaut
Author: National Aeronautics and Space Administration (NASA)
Author: Sebastian Müller
Author: Christophe Brun