Download or read book Coherent Structures in Turbulent Flames II written by Andrew J. Yule and published by . This book was released on 1980 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this investigation is to obtain increased understanding of turbulent combustion in flows related to propulsion systems. Simultaneous measurements of fluctuating velocity, temperature and local ionization level, have been made with arrays of probes, with variation in probe separations and flame initial conditions. The stored data are processed in a variety of ways, including the use of novel conditional sampling techniques. Information is thus derived on turbulent structure, eddy structure, eddy convection, eddy-reaction interaction, reaction zone structure and mixing. It is demonstrated that individually eddies can exist in flames for substantially longer distances than is apparent from classical space-time cross correlations. Similar techniques are also used in turbulent sprays and in a flame impinging ona flat plate. (Author).
Download or read book Coherent Structures in Turbulent Flames written by N. A. Chigier and published by . This book was released on 1983 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of this research was to obtain increased understanding of turbulent combustion in flows related to propulsion systems. Measurement and data analysis techniques, and the boundary conditions of various flames were designed to provide improved concepts and fundamental experimental data, to aid the development of modelling techniques for practical combustion systems. The specific approach of the study was to quantify the roles of large eddies (coherent structures) in reacting flows. The experiments and measurement techniques which have been developed to attain this aim were described in previous Interim Scientific Reports. Measurements during the past year have been made in the initial region of gaseous jet flames with separate variation in Reynolds number and equivalence ratio. These measurements have produced detailed data on the structure of the initial regions of jet diffusion flames, as a function of systematic variation of initial burner nozzle conditions. This data is already recognized to be of considerable use for combustion modelling. Two associated experiments, investigating the structures of turbulent liquid fuel sprays and impinging flames have been carried out during the period of the contract.
Download or read book Coherent Structures in Turbulent Flames written by A. J. Yule and published by . This book was released on 1979 with total page 37 pages. Available in PDF, EPUB and Kindle. Book excerpt: Diagnostic and data analysis techniques have been used to investigate the structure of turbulent jet reacting flows with well defined initial and boundary conditions. In the transition region of a turbulent jet flame a double-vortex structure has been found: with outer vortices, which may originate from Kelvin-Helmholtz or Rayleigh type instabilities, and inner vortices which are influenced strongly by one or more combustion instability mechanisms. Measurements of mean velocity, turbulence intensity, ionization current, mean temperature and peak frequencies are presented together with data derived from high speed color schlieren photography and laser schlieren spectra.
Download or read book Turbulence Coherent Structures Dynamical Systems and Symmetry written by Philip Holmes and published by Cambridge University Press. This book was released on 2012-02-23 with total page 403 pages. Available in PDF, EPUB and Kindle. Book excerpt: Describes methods revealing the structures and dynamics of turbulence for engineering, physical science and mathematics researchers working in fluid dynamics.
Download or read book Turbulent Combustion written by Norbert Peters and published by Cambridge University Press. This book was released on 2000-08-15 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt: The combustion of fossil fuels remains a key technology for the foreseeable future. It is therefore important that we understand the mechanisms of combustion and, in particular, the role of turbulence within this process. Combustion always takes place within a turbulent flow field for two reasons: turbulence increases the mixing process and enhances combustion, but at the same time combustion releases heat which generates flow instability through buoyancy, thus enhancing the transition to turbulence. The four chapters of this book present a thorough introduction to the field of turbulent combustion. After an overview of modeling approaches, the three remaining chapters consider the three distinct cases of premixed, non-premixed, and partially premixed combustion, respectively. This book will be of value to researchers and students of engineering and applied mathematics by demonstrating the current theories of turbulent combustion within a unified presentation of the field.
Download or read book Blowoff Velocity and Turbulent Flame Spread Correlations Based on Coherent Structures in Turbulent Flows written by Krishnan Radhakrishnan and published by . This book was released on 1979* with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Self sustaining Mechanisms of Wall Turbulence written by Ronald Lee Panton and published by Computational Mechanics. This book was released on 1997 with total page 448 pages. Available in PDF, EPUB and Kindle. Book excerpt: Why is wall turbulence self-sustaining? In this book well-regarded researchers not only discuss what they know and believe, but also speculate on ideas that still require numerical or experimental testing and verification. An initial brief history of boundary layer structure research is followed by chapters on experimental information and specific topics within the subject. There are then sections on computational aspects.
Download or read book Coherent Structures of Flames written by Maya Mincheva and published by . This book was released on 1996 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Turbulent Mixing in Nonreactive and Reactive Flows written by S. Murthy and published by Springer Science & Business Media. This book was released on 2013-11-11 with total page 469 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulence, mixing and the mutual interaction of turbulence and chemistry continue to remain perplexing and impregnable in the fron tiers of fluid mechanics. The past ten years have brought enormous advances in computers and computational techniques on the one hand and in measurements and data processing on the other. The impact of such capabilities has led to a revolution both in the understanding of the structure of turbulence as well as in the predictive methods for application in technology. The early ideas on turbulence being an array of complicated phenomena and having some form of reasonably strong coherent struc ture have become well substantiated in recent experimental work. We are still at the very beginning of understanding all of the aspects of such coherence and of the possibilities of incorporating such structure into the analytical models for even those cases where the thin shear layer approximation may be valid. Nevertheless a distinguished body of "eddy chasers" has come into existence. The structure of mixing layers which has been studied for some years in terms of correlations and spectral analysis is also getting better understood. Both probability concepts such as intermittency and conditional sampling as well as the concept of large scale structure and the associated strain seem to indicate possibilities of distinguishing and synthesizing 'engulfment' and molecular mixing.
Download or read book Combustion written by J. Warnatz and published by Springer Science & Business Media. This book was released on 2006-09-23 with total page 389 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a rigorous treatment of the coupling of chemical reactions and fluid flow. Combustion-specific topics of chemistry and fluid mechanics are considered and tools described for the simulation of combustion processes. This edition is completely restructured. Mathematical Formulae and derivations as well as the space-consuming reaction mechanisms have been replaced from the text to appendix. A new chapter discusses the impact of combustion processes on the atmosphere, the chapter on auto-ignition is extended to combustion in Otto- and Diesel-engines, and the chapters on heterogeneous combustion and on soot formation are heavily revised.
Download or read book Coherent Structures in the Near Field of Swirling Turbulent Jets and Flames Investigated by PIV and PLIF written by Vladimir Dulin and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The results of the experimental study of coherent flow structures in turbulent jets with different swirl rates are reported. The focus is placed on analysis of their impact on mixing of a passive scalar in the jets and on regular flame front deformations during combustion of fuel-lean and fuel-rich methane/air mixtures in case of a strongly swirling jet with vortex breakdown. The measurements are performed by applying simultaneously the particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques (acetone and HCHO for the nonreacting and reacting flows, respectively). The PIV data are processed by a proper orthogonal decomposition (POD), and the PLIF data are conditionally sampled according to the correlation coefficients of the velocity POD modes. The coherent velocity fluctuations are associated with regular patterns in the concentration fluctuation fields and flame front deformations. These patterns correspond to unsteady mixing by large-scale vortex structures in the outer mixing layer and also to variations of the entrainment rate for the flows with swirl.
Download or read book Unsteady Combustor Physics written by Tim C. Lieuwen and published by Cambridge University Press. This book was released on 2012-08-27 with total page 427 pages. Available in PDF, EPUB and Kindle. Book excerpt: Developing clean, sustainable energy systems is a pre-eminent issue of our time. Most projections indicate that combustion-based energy conversion systems will continue to be the predominant approach for the majority of our energy usage. Unsteady combustor issues present the key challenge associated with the development of clean, high-efficiency combustion systems such as those used for power generation, heating or propulsion applications. This comprehensive study is unique, treating the subject in a systematic manner. Although this book focuses on unsteady combusting flows, it places particular emphasis on the system dynamics that occur at the intersection of the combustion, fluid mechanics and acoustic disciplines. Individuals with a background in fluid mechanics and combustion will find this book to be an incomparable study that synthesises these fields into a coherent understanding of the intrinsically unsteady processes in combustors.
Download or read book Technical Abstract Bulletin written by and published by . This book was released on 1979 with total page 1186 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Journal of Vibration Testing and System Dynamics written by Jan Awrejcewicz and published by L& H Scientific Publishing. This book was released on 2018-07-01 with total page 106 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vibration Testing and System Dynamics is an interdisciplinary journal serving as the forum for promoting dialogues among engineering practitioners and research scholars. As the platform for facilitating the synergy of system dynamics, testing, design, modeling, and education, the journal publishes high-quality, original articles in the theory and applications of dynamical system testing. The aim of the journal is to stimulate more research interest in and attention for the interaction of theory, design, and application in dynamic testing. Manuscripts reporting novel methodology design for modelling and testing complex dynamical systems with nonlinearity are solicited. Papers on applying modern theory of dynamics to real-world issues in all areas of physical science and description of numerical investigation are equally encouraged. Progress made in the following topics are of interest, but not limited, to the journal: Vibration testing and designDynamical systems and controlTesting instrumentation and controlComplex system dynamics in engineeringDynamic failure and fatigue theoryChemical dynamics and bio-systemsFluid dynamics and combustionPattern dynamicsNetwork dynamicsPlasma physics and plasma dynamicsControl signal synchronization and trackingBio-mechanical systems and devicesStructural and multi-body dynamicsFlow or heat-induced vibrationMass and energy transfer dynamicsWave propagation and testing
Download or read book Turbulent Premixed Flames written by Nedunchezhian Swaminathan and published by Cambridge University Press. This book was released on 2011-04-25 with total page 447 pages. Available in PDF, EPUB and Kindle. Book excerpt: A work on turbulent premixed combustion is important because of increased concern about the environmental impact of combustion and the search for new combustion concepts and technologies. An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts. Lean premixed flames have the potential to offer ultra-low emission levels, but they are notoriously susceptible to combustion oscillations. Thus, sophisticated control measures are inevitably required. The editors' intent is to set out the modeling aspects in the field of turbulent premixed combustion. Good progress has been made on this topic, and this cohesive volume contains contributions from international experts on various subtopics of the lean premixed flame problem.
Download or read book Coherent Structures in Complex Systems written by D. Reguera and published by Springer. This book was released on 2008-01-11 with total page 466 pages. Available in PDF, EPUB and Kindle. Book excerpt: A rich variety of real-life physical problems which are still poorly understood are of a nonlinear nature. Examples include turbulence, granular flows, detonations and flame propagation, fracture dynamics, and a wealth of new biological and chemical phenomena which are being discovered. Particularly interesting among the manifestations of nonlinearity are coherent structures. This book contains reviews and contributions reporting on the state of the art regarding the role of coherent structures and patterns in nonlinear science.
Download or read book Interactions Between Coherent and Turbulent Oscillations and Their Impact on the Dynamics of Flames and Flow Fields written by Ashwini Karmarkar and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This primary focus of this dissertation is to investigate the coupling mechanisms by which flow field fluctuations can interact with heat release oscillations and how the coupling mechanisms are impacted by the addition of turbulent fluctuations. This work is particularly motivated by the problem of combustion instability in gas turbine engines. Combustion instability is a type of thermoacoustic instability that occurs due to coupling between the coherent oscillations in heat release rate and the acoustic modes of the combustor. The modulation of heat release rate due to the interaction of the flame front with coherent structures in the flow can be a driver of combustion instability. While there have multiple studies analysing the interaction between flames and coherent structures, many of the experimental studies focus on the low-turbulence regime, which is not representative of realistic engine conditions. More recent studies have analysed flame response and limiting phenomena at high turbulence intensities, although the interaction between competing phenomena of turbulent and coherent oscillations have not been comprehensively studied so far and is therefore a focus contribution of this work. In this dissertation, two configurations are studied -- the canonical rod-stabilized V-flame and a more realistic partially-premixed swirl flame. The canonical configuration allows for more control over individual flow parameters so that the coherent and turbulent fluctuations can be independently controlled and systematically varied. High-speed stereoscopic particle image velocimetry (sPIV) is the primary diagnostic used in this configuration. The coherent oscillations in the flow field are excited by longitudinal acoustic excitation and different configurations of perforated plates in the burner provide varying turbulence intensities. The results from this work conclusively show that the magnitude of turbulence intensity in the flow can significantly impact the flow dynamics, the symmetry of the flow response to external excitation, and the coupling between the flow field and flame fluctuations. The realistic swirling flame configuration is used to characterize the interaction between the precessing vortex core (PVC), which is the consequence of a global hydrodynamic instability, and thermoacoustic instabilities, which are the result of a coupling between combustor acoustics and the unsteady heat release rate of combustion. This study is performed using experimental data obtained from a model gas turbine combustor system to simulate realistic conditions. High-speed stereoscopic particle image velocimetry, OH planar laser-induced fluorescence, and acetone planar laser-induced fluorescence are used to obtain information about the velocity fields, flame, and fuel flow behavior, respectively. The results from this work show that in the cases where the frequency of the PVC overlaps with the frequency of a thermoacoustic mode, the thermoacoustic mode is subsequently suppressed. Further, the thermoacoustic coupling process is driven by both velocity and mixture variations, but the PVC oscillations do not significantly drive variations in the mixture, only the velocity field. Put together, the findings from both configurations provide important insight into the coupling mechanisms that govern the interactions between the various flow field fluctuations and their impact on the unsteady heat release from the flame.
