Author: Qiang An
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The coupling between hydrodynamic instability and flame lift-off in premixed swirl combustion was investigated in a gas turbine model combustor using multi-kHz repetition-rate OH* chemiluminescence (CL), OH planar laser induced fluorescence (PLIF), and stereoscopic particle image velocimetry (S-PIV). Over 60 different combinations of fuel composition, equivalence ratio, and reactant preheat temperature were studied, allowing systematic variation of the reactant-to-product density ratio, laminar flame speed, and Lewis number. Depending on the test conditions, the flame could either be stably attached to the nozzle, stably lifted, or intermittently transitioning between attached and lifted states. Transition between stabilization states was linked with the transition between convective and absolute instability at the flame base; formation of an $m=1$ ($m$ denotes the azimuthal wavenumber) globally unstable wave was associated with the lifted flame, manifested by a helical precessing vortex core (PVC). A detailed physical mechanism, involving density stratification, local extinction, strain rate, and PVC formation, was proposed to elucidate swirl flame lift-off. The minimum bulk velocity at which the flame was stably lifted was linearly correlated with the laminar flame extinction strain rate, while none of the other commonly reported key parameters governing hydrodynamic instability was able to collapse the data alone. Hence, lift-off was associated with a relatively constant Damk\"{o}hler number based on the bulk fluid strain rate and extinction strain rate. The roles of local strain and extinction on the transition process were further explained by the test conditions with intermittent lift-off/reattachment. The probability of the flame being in the lifted state was roughly linearly correlated with the degree of local extinction at the flame base while the flame was still attached. Moreover, this probability also was linearly related to the ratio of fluid-dynamic strain rate to extinction strain rate, but not the fluid-dynamic strain rate itself. In addition, using visibility graph, transition from the attached to the lifted regime was found to be associated with the transition from a scale-free to a regular network via intermittency. Intermittency was further quantified using spatially extended networks. It was shown that prediction of hydrodynamic instability limits might be possible using certain network measures.
Author: Tim C. Lieuwen
Publisher: Cambridge University Press
ISBN: 1139576836
Category : Technology & Engineering
Languages : en
Pages : 427
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Book Description
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.
Author: Paul Palies
Publisher: Academic Press
ISBN: 0128199970
Category : Technology & Engineering
Languages : en
Pages : 402
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Book Description
Stabilization and Dynamic of Premixed Swirling Flames: Prevaporized, Stratified, Partially, and Fully Premixed Regimes focuses on swirling flames in various premixed modes (stratified, partially, fully, prevaporized) for the combustor, and development and design of current and future swirl-stabilized combustion systems. This includes predicting capabilities, modeling of turbulent combustion, liquid fuel modeling, and a complete overview of stabilization of these flames in aeroengines. The book also discusses the effects of the operating envelope on upstream fresh gases and the subsequent impact of flame speed, combustion, and mixing, the theoretical framework for flame stabilization, and fully lean premixed injector design. Specific attention is paid to ground gas turbine applications, and a comprehensive review of stabilization mechanisms for premixed, partially-premixed, and stratified premixed flames. The last chapter covers the design of a fully premixed injector for future jet engine applications. Features a complete view of the challenges at the intersection of swirling flame combustors, their requirements, and the physics of fluids at work Addresses the challenges of turbulent combustion modeling with numerical simulations Includes the presentation of the very latest numerical results and analyses of flashback, lean blowout, and combustion instabilities Covers the design of a fully premixed injector for future jet engine applications
Author: Ashwini Karmarkar
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
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.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 39
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Book Description
Hydrodynamic (Landau) instability in combustion is typically associated with the onset of wrinkling of a flame surface, corresponding to the formation of steady cellular structures as the stability threshold is crossed. In the context of liquid-propellant combustion, such instability has recently been shown to occur for critical values of the pressure sensitivity of the burning rate and the disturbance wavenumber, significantly generalizing previous classical results for this problem that assumed a constant normal burning rate. Additionally, however, a pulsating form of hydrodynamic instability has been shown to occur as well, corresponding to the onset of temporal oscillations in the location of the liquid/gas interface. In the present work, we consider the realistic influence of a nonzero temperature sensitivity in the local burning rate on both types of stability thresholds. It is found that for sufficiently small values of this parameter, there exists a stable range of pressure sensitivities for steady, planar burning such that the classical cellular form of hydrodynamic instability and the more recent pulsating form of hydrodynamic instability can each occur as the corresponding stability threshold is crossed. For larger thermal sensitivities, however, the pulsating stability boundary evolves into a C-shaped curve in the (disturbance-wavenumber, pressure-sensitivity) plane, indicating loss of stability to pulsating perturbations for all sufficiently large disturbance wavelengths. It is thus concluded, based on characteristic parameter values, that an equally likely form of hydrodynamic instability in liquid-propellant combustion is of a nonsteady, long-wave nature, distinct from the steady, cellular form originally predicted by Landau.
Author: Toufik Boushaki
Publisher: BoD – Books on Demand
ISBN: 1838807438
Category : Science
Languages : en
Pages : 120
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Book Description
Swirl flows are used in a wide range of industrial applications. In non-reacting cases, examples of applications include vortex amplifiers and reactors, heat exchangers, jet pumps, and cyclone separators. In reacting cases, swirlers are widely used in combustion systems, such as gas turbines, industrial furnaces, boilers, gasoline and diesel engines, and many other practical heating devices. Effects of using swirl on flow and combustion are significant and varied, and concern, for example, aerodynamics, mixing, flame stability, intensity of combustion, and pollutant emissions. The purpose of this book is to present recent research efforts to understand and characterize swirling flows of different types and in different applications. These include gaseous, liquid, and solid fuels in order to enhance combustion systems and their energy efficiency. Swirl flows are very complex and the studies proposed in this project are based on different means, including theoretical calculations, numerical modeling, and experimental measurements.
Author: Rajavasanth Rajasegar
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: Timothy C. Lieuwen
Publisher: AIAA (American Institute of Aeronautics & Astronautics)
ISBN:
Category : Science
Languages : en
Pages : 688
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Book Description
This book offers gas turbine users and manufacturers a valuable resource to help them sort through issues associated with combustion instabilities. In the last ten years, substantial efforts have been made in the industrial, governmental, and academic communities to understand the unique issues associated with combustion instabilities in low-emission gas turbines. The objective of this book is to compile these results into a series of chapters that address the various facets of the problem. The Case Studies section speaks to specific manufacturer and user experiences with combustion instabilities in the development stage and in fielded turbine engines. The book then goes on to examine The Fundamental Mechanisms, The Combustor Modeling, and Control Approaches.
Author: A. Davenas
Publisher: Newnes
ISBN: 0080984754
Category : Technology & Engineering
Languages : en
Pages : 623
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Book Description
This book, a translation of the French title Technologie des Propergols Solides, offers otherwise unavailable information on the subject of solid propellants and their use in rocket propulsion. The fundamentals of rocket propulsion are developed in chapter one and detailed descriptions of concepts are covered in the following chapters. Specific design methods and the theoretical physics underlying them are presented, and finally the industrial production of the propellant itself is explained. The material used in the book has been collected from different countries, as the development of this field has occurred separately due to the classified nature of the subject. Thus the reader not only has an overall picture of solid rocket propulsion technology but a comprehensive view of its different developmental permutations worldwide.
Author: Mariia Sobulska
Publisher: CRC Press
ISBN: 1000454916
Category : Technology & Engineering
Languages : en
Pages : 142
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Book Description
Drying processes are among the most energy-consuming operations in industry. Flame spray drying (FSD) is a novel approach to reduce the energy supply needed for the spray drying process. Flame Spray Drying: Equipment, Mechanism, and Perspectives describes FSD technology and current developments in flame techniques and evaluates potential industrial implementation. Details advantages of FSD in terms of energy consumption and reduced drying time Promotes applications of biofuels for the drying process Analyzes the FSD method from CFD modelling to product quality Evaluates potential safety and product degradation risks Provides examples of potential applications of the FSD technique in drying of different materials This book describes an important new technique that is useful to chemical and process engineering researchers, professionals, and students working with drying technologies.
