Download or read book Systematic Investigation of Bluff Body Combustion Instability written by and published by . This book was released on 2005 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objectives, work carried out and results obtained during a Phase 11 STTR project are reported. An capability for unsteady flows is added to a sensitivity tool which numerically solves the continuous sensitivity equations. A feedback control law is implemented to control numerically an acoustic instability, which is modeled by coupling pressure and velocity perturbations at an inflow boundary condition. Axi-symmetric simulations are presented for the burner both without methane injection and with five injection locations. The computation is performed using a 12-specie methane/air chemistry model with finite-rate chemical kinetics. An experimental investigation is pursued of a circular bluff-body burner equipped with multiple fuel injectors. The axial injector is used as a pilot flame for premixed observations at equivalence ratios of 0.4 and 0.5.

Download or read book Dynamical Characteristics of Reacting Bluff Body Wakes written by Benjamin L. Emerson and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Combustion instability plagues the combustion community in a wide range of applications. This un-solved problem is especially prevalent and expensive in aerospace propulsion and ground power generation. The challenges associated with understanding and predicting combustion instability lie in the flame response to the acoustic field. One of the more complicated flame response mechanisms is the velocity coupled flame response, where the flame responds dynamically to the acoustic velocity as well as the vortically induced velocity field excited by the acoustics. This vortically induced, or hydrodynamic, velocity field holds critical importance to the flame response but is computationally expensive to predict, often requiring high fidelity CFD computations. Furthermore, its behavior can be a strong function of the numerous flow parameters that change over the operability map of a combustor. This research focuses on a nominally two dimensional bluff body combustor, which has rich hydrodynamic stability behavior with a manageable number of stability parameters. The work focuses first on experimentally characterizing the dynamical flow and flame behavior. Next, the research shifts focus toward hydrodynamic stability theory, using it to explain the physical phenomena observed in the experimental work. Additionally, the hydrodynamic stability work shows how the use of simple, model analysis can identify the important stability parameters and elucidate their governing physical roles. Finally, the research explores the forced response of the flow and flame while systematically varying the underlying hydrodynamic stability characteristics. In the case of longitudinal combustion instability of highly preheated bluff body combustors, it shows that conditions where an acoustic mode frequency equals the hydrodynamic global mode frequency are not especially dangerous from a combustion instability standpoint, and may actually have a reduced heat release response. This demonstrates the very non-intuitive role that the natural hydrodynamic flow stability plays in the forced heat release response of the flame. For the fluid mechanics community, this work contributes to the detailed understanding of both unforced and forced bluff body combustor dynamics, and shows how each is influenced by the underlying hydrodynamics. In particular, it emphasizes the role of the density-shear layer offset, and shows how its extreme sensitivity leads to complicated flow dynamics. For the flow-combustor community as a whole, the work reviews a pre-existing method to obtain the important flow stability parameters, and demonstrates a novel way to link those parameters to the governing flow physics. For the combustion instability community, this thesis emphasizes the importance of the hydrodynamic stability characteristics of the flow, and concludes by offering a paradigm for consideration of the hydrodynamics in a combustion instability problem.

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 Experimental Investigation Into Thermo Acoustic Instability in Pre Mixed Pre Vaporized Bluff Body Stabilized Flames written by Jeffrey Ross Monfort and published by . This book was released on 2015 with total page 277 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental campaign was undertaken to investigate the thermo-acoustic properties of a bluff-body stabilized flame in an atmospheric pressure facility at the Air Force Research Laboratory. Of particular interest were the possible interactions between the acoustic properties of the test rig, the vortex shedding due to the presence of the bluff-body, and the unsteady heat release within the chamber. An analysis of the vortex shedding modes due to the bluff-body and the acoustic modes indicated that there are regions in the operating envelope where the two mode types share similar frequencies given an operating condition, creating a scenario where feedback might be possible. Further investigation into the fluctuating velocity components in the wake of the bluff-body indicated that the Strouhal number is not single-valued, and that vortices of varying sizes, and accompanying characteristic frequencies, are shed from a single bluff-body.With previous research indicating that lean blow-off is preceded by local extinctions within the reaction zone, and blow-off being closely related to the ratio of chemical and fluidic time scales, an experiment was conducted to determine whether or not flames undergoing thermo-acoustic instability also exhibit regions of decreased residence time. This experiment concluded that the regions of acoustically-coupled flames which undergo large-scale oscillations do, in fact, correlate with decreased residence time. This conclusion links both lean static stability and near-stoichiometric dynamic stability to simple time scales prescribed by vortex behavior in the wake of a bluff-body.An investigation was conducted which utilized simultaneous high-speed particle image velocimetry (PIV), planar laser-induced fluorescence (PLIF) and pressure measurements in the near-wake region of a bluff-body stabilized flame. In addition to the simultaneous measurements listed, high-speed broadband chemiluminescence was also collected. The 2-D nature of these measurements led to their analysis through the utilization of proper orthogonal decomposition (POD). The decomposition of the highly-complicated data sets allowed the dominant features to be extracted. These dominant features, in an acoustically-coupled flame, show remarkable symmetry that is not readily apparent in uncoupled flames. Further analysis of an objective measure of the flame symmetry as a function of equivalence ratio indicated that the fluctuations in the axial component of velocity best correlate with overall sound pressure level. This correlation indicates that the feedback interactions are based around the longitudinal acoustic modes of the combustion chamber.

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 NBS Special Publication written by and published by . This book was released on 1978 with total page 520 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Analysis of Blowoff Scaling of Bluff Body Stabilized Flames written by Sajjad A. Husain and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Bluff body stabilization of flames is a commonly employed technique for combustion applications, such as thrust augmentors. These combustors are usually required to operate at lean conditions governed by a lower stability limit on combustion denoted by lean blow off. Lean blow off is believed to be a dynamically unstable phenomenon that leads to flame extinction or convection from a stable, usually desired, point in space. Current theories predict lean blow off based on models that were developed over specific domain of inflow parameters. This thesis sought to compile, re-evaulate, and analyze past blowoff data presented in literature using time scale correlations, Damkohler numbers, by employing modern chemical kinetic solvers to approximate characteristic chemical times. The research has conclusively shown that it is possible to express blowoff data for multiple flow conditions using a power law relationship between Damkohler number and Reynolds numbers. From the analysis of this power law relations, trends are validated using past empirical observations, and some new information regarding flame stability is also conveyed.

Download or read book Hydraulic Research in the United States and Canada written by United States. National Bureau of Standards and published by . This book was released on 1976 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Hydraulic Research in the United States and Canada 1976 written by Pauline H. Gurewitz and published by . This book was released on 1978 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effects of Combustion Chamber Blockage on Bluff Body Flame Stabilization written by James Roger Foster and published by . This book was released on 1956 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Investigation of Combustion Instability in Confined Flames written by James Oghenowede Asalor and published by . This book was released on 1972 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Experimental Investigation of Flame Spreading from Bluff Body Flameholders written by Dick W. Thurston and published by . This book was released on 1958 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Experimental Investigation of Flame Spreading from Bluff Body Flameholders written by Dick W. Thurston and published by . This book was released on 1958 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Joint Meeting of the U S Sections of the Combustion Institute Western States Central States Eastern States written by and published by . This book was released on 1999 with total page 954 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book LES of Bluff Body Stabilized Premixed and Partially Premixed Combustion written by Ionut Porumbel and published by VDM Publishing. This book was released on 2008 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt: The main topic of this work is the study of the equivalence ratio effect on flame stability and dynamics in premixed and partially premixed flames by means of an LES algorithm able to handle the entire range of combustion regimes, with no ad-hoc adjustable parameters and able to respond automatically to variations in the inflow conditions.

Download or read book International Aerospace Abstracts written by and published by . This book was released on 1999 with total page 1020 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Dynamics of Longitudinally Forced Bluff Body Flames with Varying Dilatation Ratios written by Dmitriy Vital Plaks and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis focuses on experimentally measuring the response of varying dilatation ratio bluff body flames under harmonic excitation. Such flames are often encountered in jet engine afterburners and are susceptible to combustion instabilities. Previous work has been done modeling such flames, however, only limited experimental data has been obtained at these conditions and is the motivation for this thesis.