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.

Download or read book Turbulence and Interactions written by Michel O. Deville and published by Springer. This book was released on 2014-06-13 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book presents a snapshot of the state-of-art in the field of turbulence modeling and covers the latest developments concerning direct numerical simulations, large eddy simulations, compressible turbulence, coherent structures, two-phase flow simulation and other related topics. It provides readers with a comprehensive review of both theory and applications, describing in detail the authors’ own experimental results. The book is based on the proceedings of the third Turbulence and Interactions Conference (TI 2012), which was held on June 11-14 in La Saline-les-Bains, La Réunion, France and includes both keynote lectures and outstanding contributed papers presented at the conference. This multifaceted collection, which reflects the conference ́s emphasis on the interplay of theory, experiments and computing in the process of understanding and predicting the physics of complex flows and solving related engineering problems, offers a practice-oriented guide for students, researchers and professionals in the field of computational fluid dynamics, turbulence modeling and related areas.

Download or read book Dynamics of Interacting Turbulent Flames written by Ankit Tyagi and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation investigates the physics of interactions between turbulent premixed flames. It is known that multiple flame configurations provide better stability characteristics compared to a large single-flame. However, the advantages of multiple flames are limited by flame proximity as flame-flame interactions tend to reduce the burning efficiency of the reactant gases. Previous studies have shown that interactions between multiple flames directly impact the flame structure and its propagation, resulting in reduced burning efficiency. Previous experimental studies of interacting flames addressed flame-flame interactions investigating their effects on combustor stability and efficiency from a global perspective. However, the local flame-flame interaction physics was not addressed comprehensively, in part because these studies were limited to specific flow and flame configurations. In particular, these studies focused on swirling flames in bluff-body configurations typical of modern combustor geometries. Furthermore, these studies lacked flowfield measurements and were limited to flame structure and heat release rate measurements due to the complex nature of the experimental configurations. Much of the work to date on understanding the local physics of interactions comes from direct numerical simulations (DNS), but these studies treated idealized configurations of limited practical utility.To bridge these two gaps, an experimental investigation of flame-flame interactions was performed using a dual-burner rig, composed of two flames, built to facilitate precise variations in flame spacing. This rig was designed to operate in different configurations. These facilitated the focus on local interaction physics. In particular, the rig was built to study interacting V-flames and Bunsen flames. Moreover, the design of the dual-burners permitted conducting studies of nonreacting flow interactions with flames to better understand local physics of the flame. Direct flame and flow measurements were performed to characterize the mutual interaction of flame and the local flowfield. In particular, flame structure and flow were characterized using synchronized OH-planar laser-induced fluorescence (OH-PLIF) and stereoscopic-particle image velocimetry (s-PIV). These measurements were performed at a sampling rate of 10 kHz to obtain converged statistics on flame-flame interactions. A novel image processing technique was implemented for robust detection and characterization of flame-flame interaction events from OH-PLIF images.Using this experimental approach, the following studies were conducted: i) effects of flame spacing on flame structure of interacting V-flames, ii) effects of multiple flames on frequency, topology, and orientation of local flame-flame interactions, iii) effects of high mean-shear flow on flame-flame interactions, and iv) effects of pocket formation on flame dynamics. In the first study, flame spacing variations in V-flames were found to directly impact flame attachment. For smaller flame spacings, recirculation of hot combustion products near the bluff-bodies facilitated a secondary flame branch attachment in the shear layers in the interaction regions. For larger flame spacing, the secondary attachment became intermittent, indicating that closer flame spacing resulted in better attachment and stability characteristics for these flames. In the second study, the presence of adjacent flames was found to directly impact the frequencies of flame-flame interaction events. Dual-flames showed lower reactant-side interactions rates and higher product-side interactions rates when compared with single-flames. For dual-flames, comparisons between interaction orientation and local strain rate orientation showed that compressive forces led to flame front merging or pinch-off. The third study, which focused on how mean shear affects the local flame dynamics, found that high-mean shear flows entrained the flame away from the center of the burner. This entrainment directly reduced interaction event frequencies along the flame branch closest to the high mean-shear flow, while interaction event frequency in the other branch increased. Finally, flame pocket formation was investigated and results showed that a majority of the reactant pockets burned-out, while a majority of the product pockets merged with the flame surface. These results suggested that pocket behavior in turbulent flames can change local flame dynamics and it is important to capture these effects to accurately predict flame behavior. Additionally, limitations of planar high-speed imaging techniques were explored and a statistical framework, using probabilistic models, was presented in the context of reactant pocket propagation. The outcome of this work provided improved uncertainty estimation for planar measurements in three-dimensional flows.This experimental investigation provided deeper insights into the local physics of flame-flame interactions, in practical configurations, using detailed flame and flow measurements. The presence of adjacent flames influenced the attachment characteristics and local flame structure that directly impacted the stability of these multiple flame configurations. Local compressive forces facilitated the occurrence of these events, highlighting the importance of changes to the flowfield due to adjacent flames. Pocket formation, which directly affected reactant gas burning efficiency, was found to occur frequently. Taken together, these results provided comprehensive insights into the effects of flame-flame interactions that enhance our understanding of the nature of interacting flames.

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 Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 440 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Applied mechanics reviews written by and published by . This book was released on 1948 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Thermoacoustic Instability written by R. I. Sujith and published by Springer Nature. This book was released on 2021-12-14 with total page 484 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book systematically presents the consolidated findings of the phenomenon of self-organization observed during the onset of thermoacoustic instability using approaches from dynamical systems and complex systems theory. Over the last decade, several complex dynamical states beyond limit cycle oscillations such as quasiperiodicity, frequency-locking, period-n, chaos, strange non-chaos, and intermittency have been discovered in thermoacoustic systems operated in laminar and turbulent flow regimes. During the onset of thermoacoustic instability in turbulent systems, an ordered acoustic field and large coherent vortices emerge from the background of turbulent combustion. This emergence of order from disorder in both temporal and spatiotemporal dynamics is explored in the contexts of synchronization, pattern formation, collective interaction, multifractality, and complex networks. For the past six decades, the spontaneous emergence of large amplitude, self-sustained, tonal oscillations in confined combustion systems, characterized as thermoacoustic instability, has remained one of the most challenging areas of research. The presence of such instabilities continues to hinder the development and deployment of high-performance combustion systems used in power generation and propulsion applications. Even with the advent of sophisticated measurement techniques to aid experimental investigations and vast improvements in computational power necessary to capture flow physics in high fidelity simulations, conventional reductionist approaches have not succeeded in explaining the plethora of dynamical behaviors and the associated complexities that arise in practical combustion systems. As a result, models and theories based on such approaches are limited in their application to mitigate or evade thermoacoustic instabilities, which continue to be among the biggest concerns for engine manufacturers today. This book helps to overcome these limitations by providing appropriate methodologies to deal with nonlinear thermoacoustic oscillations, and by developing control strategies that can mitigate and forewarn thermoacoustic instabilities. The book is also beneficial to scientists and engineers studying the occurrence of several other instabilities, such as flow-induced vibrations, compressor surge, aeroacoustics and aeroelastic instabilities in diverse fluid-mechanical environments, to graduate students who intend to apply dynamical systems and complex systems approach to their areas of research, and to physicists who look for experimental applications of their theoretical findings on nonlinear and complex systems.

Download or read book Japanese Science and Technology written by and published by . This book was released on 1986 with total page 724 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Thermoacoustic Combustion Instability Control written by Dan Zhao and published by Academic Press. This book was released on 2023-02-13 with total page 1145 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thermoacoustic Combustion Instability Control: Engineering Applications and Computer Codes provides a unique opportunity for researchers, students and engineers to access recent developments from technical, theoretical and engineering perspectives. The book is a compendium of the most recent advances in theoretical and computational modeling and the thermoacoustic instability phenomena associated with multi-dimensional computing methods and recent developments in signal-processing techniques. These include, but are not restricted to a real-time observer, proper orthogonal decomposition (POD), dynamic mode decomposition, Galerkin expansion, empirical mode decomposition, the Lattice Boltzmann method, and associated numerical and analytical approaches. The fundamental physics of thermoacoustic instability occurs in both macro- and micro-scale combustors. Practical methods for alleviating common problems are presented in the book with an analytical approach to arm readers with the tools they need to apply in their own industrial or research setting. Readers will benefit from practicing the worked examples and the training provided on computer coding for combustion technology to achieve useful results and simulations that advance their knowledge and research. Focuses on applications of theoretical and numerical modes with computer codes relevant to combustion technology Includes the most recent modeling and analytical developments motivated by empirical experimental observations in a highly visual way Provides self-contained chapters that include a comprehensive, introductory section that ensures any readers new to this topic are equipped with required technical terms

Download or read book Flow Control written by Mohamed Gad-el-Hak and published by Springer Science & Business Media. This book was released on 2003-07-01 with total page 533 pages. Available in PDF, EPUB and Kindle. Book excerpt: No be certain it can is not based mathematics. knowledge if upon da Vinci, (Leonardo 1452 1519) the humankind. Thinking is one greatest of Joys of Galilei, (Galileo 1564 1642) Now I think is to be the root all hydrodynamics and is at of physical science, second the to none in its mathematics. present beauty of Thomson (William (Lord Kelvin), 1824 1907) The book contains the lecture notes of of the nine instructors at present eight the short Flow Control: Fundamentals and which held course was Practices, in the week 24 28 June and Carg6se, Corsica, France, during 1996, repeated at the of Notre 9 13 1996. University Dame, Indiana, September Following the week in the course a on same was held. Corsica, 5 day workshop topic Selected from the scheduled to 1998 workshop are papers appear early special volume of the International Journal Heat Thermo of Experimental Transfer, and Fluid All Mechanics. three events were Jean Paul dynamics, organized by Bonnet of Universit6 de Andrew Pollard of Univer Poitiers, France, Queen's at and Mohamed Gad el Hak of the of sity Kingston, Canada, University Notre U.S.A.

Download or read book Lecture Notes on Turbulence and Coherent Structures in Fluids Plasmas and Nonlinear Media written by Michael Shats and published by World Scientific. This book was released on 2006 with total page 397 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is based on the lectures delivered at the 19th Canberra International Physics Summer School held at the Australian National University in Canberra (Australia) in January 2006.The problem of turbulence and coherent structures is of key importance in many fields of science and engineering. It is an area which is vigorously researched across a diverse range of disciplines such as theoretical physics, oceanography, atmospheric science, magnetically confined plasma, nonlinear optics, etc. Modern studies in turbulence and coherent structures are based on a variety of theoretical concepts, numerical simulation techniques and experimental methods, which cannot be reviewed effectively by a single expert.The main goal of these lecture notes is to introduce state-of-the-art turbulence research in a variety of approaches (theoretical, numerical simulations and experiments) and applications (fluids, plasmas, geophysics, nonlinear optical media) by several experts. A smooth introduction is presented to readers who are not familiar with the field, while reviewing the most recent advances in the area. This collection of lectures will provide a useful review for both postgraduate students and researchers new to the advancements in this field, as well as specialists seeking to expand their knowledge across different areas of turbulence research.

Download or read book AIAA Journal written by American Institute of Aeronautics and Astronautics and published by . This book was released on 2006 with total page 958 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Analysis of Inter scale Turbulence Chemistry Dynamics with Reduced Physics Simulations for Application to Large Eddy Simulation of Premixed Turbulent Combustion written by Paulo Lucena Kreppel Paes and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Large Eddy Simulation (LES) is a powerful formulation to model turbulent reacting flows with tradeoffs between complexity and resolution. The classical LES framework assumes that the evolution of the more energetic grid-filtered motions are dominated by the dynamical interactions that are explicitly resolved on an "effective grid" that incorporates implicit and/or explicit filtering at the smallest grid-resolvable scales by non-physical friction introduced by the numerical algorithm and modeled terms. The dynamical effects of the unresolved Sub-Filter-Scale (SFS) motions on the evolution of the Resolved-Scale (RS) motions are higher order modulations. However, the application of the classical LES framework to turbulent reacting flows is not clear since dynamically first-order chemical kinetics associated with heat release reside within mostly unresolved SFS thin flame regions. Consequently, key dynamics underlying the function of combustion devices often reside dominantly within unresolved SFS motions in contradiction to the fundamental requirement underlying accurate prediction of resolved-scale dynamics with LES. Furthermore, the topological structure of the flame is necessarily frontal in nature (i.e., sheet-like structure), which poses difficulties for an LES strategy that must model coherent structures that live partially in resolved and partially in subfilter scale fluctuations with a method that treats turbulence eddies as either resolved or subfilter scale. In my research program, we explore the introduction of new modeling elements embedded within current state-of-the-art LES frameworks to capture the impacts of the dynamically dominant inter-scale couplings between RS and SFS motions to improve the predictive accuracy of premixed turbulent combustion evolution at the resolved scales. We aim to systematically refine understanding of the inter-scale interactions between coherent structural features in physical space and in scale space in LES of premixed turbulent combustion. Given the complexity of the interaction between a flame and a complete range of turbulence eddy scales, we analyze reduced physics two-dimensional simulations of the interactions between single-scale vortex arrays and laminar premixed flames, with systematically increasing relative vortex strength creating higher complexity in flame corrugation. To characterize physical-scale space relationships, we apply the Fourier description using a newly developed procedure that removes the broadband Fourier spectral content associated with boundary discontinuities in the non-periodic directions of variables simulated within a finite domain without significant modification of the scales of interest in the original signals. This procedure allows for the analysis of any signal with the Fourier spectral decomposition regardless of the boundary conditions. Using Fourier-space filters, we identify characteristic coherent structural features concurrently in physical and Fourier space in response to flame-eddy interaction and their relative contributions to the SFS and RS variance content of the primary variables of interest. Momentum, energy and species concentrations display different distinct structural features that undergo systematic transition from weak to strong flame-vortex interactions. The primary variables within the dynamical system were classified based on the RS vs. SFS variance content, and distinct structural features in physical and Fourier space were identified for each class. We show that the SFS variance for all variables analyzed is associated with the SFS corrugated flame front, which in 2D Fourier space is associated with a coherent broadband "star-like" pattern that extends from the resolved to the flame subfilter scales. The directional dependences, magnitudes and phase relationships among the Fourier coefficients within the "legs" of the star reflect the power-law spectral representation of fronts and are shown to be closely connected with the direction and magnitude of flame-normal gradients of key variables within the corrugated flame front. We take advantage of the mathematical simplicity of the Fourier spectral description of the nonlinearities in the equations of motion to identify the dominant nonlinear couplings between SFS and RS fluctuations, and from these the SFS content involved in the dominant SFS-RS interactions. In Fourier space the nonlinear terms appear as sums of elemental scale interactions each of which have a well-defined geometrical relationship among wave vectors that form polygons in multidimensional Fourier space. Whereas the shape of the polygon is triangular within advective nonlinearities (triads), it is quadrangular for the chemical nonlinearities (quadrads). This elemental representation of key nonlinearities is used to develop a novel strategy to arrange and down-select the dominant nonlinear inter-scale couplings between SFS and RS motions, from which the corresponding SFS content associated with dynamically dominant RS-SFS dynamics are extracted. The procedure is applied to advective, triadic, and chemical, quadratic, nonlinearities within the LES-filtered governing equations. For primary variables that have most of its energy content at large scales and rapid drops in energy towards small scale, the large-scale features of the dynamically dominant SFS content are shown to be coupled with the smallest resolved scales leading to the corrugations and thickness of the RS flame front. In contrast, the dynamically dominant SFS content of intermediate species involved in heat release rate is shown to follow the smallest corrugations of the flame front reaction zone, which deviate from the RS flame centerline in regions with higher corrugations, such as the flame cusps. The distinct structural features of dynamically dominant SFS content are used for the development of simplified mathematical representations that could be applied within a modeling strategy that directly embeds the interaction between the modeled dominant SFS content and RS evolution within existing LES frameworks to improve the dynamical evolution of resolved-scale motions. From our analysis we develop a number of primary mathematical forms that encapsulate dominant SFS content of momentum, energy and key species variables within advective nonlinearities and show that these produce significant improvements in the time derivatives underlying evolution of the resolved scales. The analysis demonstrates the potential for incorporating directly key energetic and structural features of SFS that significantly impact the evolution of RS motions through key nonlinear dynamic couplings in LES frameworks employing highly simplified mathematical representations. This research lays the groundwork for a Galerkin-like modeling strategy that incorporates highly reduced numbers of basis functions that encapsulate previously determined dominant nonlinear couplings between subfilter-scale structure and resolved-scale evolution.

Download or read book Unsteady Combustor Physics written by Tim C. Lieuwen and published by Cambridge University Press. This book was released on 2021-10-21 with total page 533 pages. Available in PDF, EPUB and Kindle. Book excerpt: Explore a unified treatment of the dynamics of combustor systems, including acoustics, fluid mechanics, and combustion in a single rigorous text. This updated new edition features an expansion of data and experimental material, updates the coverage of flow stability, and enhanced treatment of flame dynamics. Addresses system dynamics of clean energy and propulsion systems used in low emissions systems. Synthesizing the fields of fluid mechanics and combustion into a coherent understanding of the intrinsically unsteady processes in combustors. This is a perfect reference for engineers and researchers in fluid mechanics, combustion, and clean energy.

Download or read book International Aerospace Abstracts written by and published by . This book was released on 1998 with total page 980 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Japanese Science and Technology 1983 1984 written by United States. National Aeronautics and Space Administration. Scientific and Technical Information Branch and published by . This book was released on 1985 with total page 1080 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Recent Awards in Engineering written by and published by . This book was released on 1983 with total page 986 pages. Available in PDF, EPUB and Kindle. Book excerpt: