Towards Predicting Dynamics in Turbulent Premixed Combustion Using PIV-PLIF Measurements of Flow-flame Microstructure

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ISBN 13 :
Total Pages : 216 pages
Book Rating : 4.:/5 (897 download)

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Book Synopsis Towards Predicting Dynamics in Turbulent Premixed Combustion Using PIV-PLIF Measurements of Flow-flame Microstructure by : Seung Hyuck Hong

Download or read book Towards Predicting Dynamics in Turbulent Premixed Combustion Using PIV-PLIF Measurements of Flow-flame Microstructure written by Seung Hyuck Hong and published by . This book was released on 2014 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt: Combustion dynamics are critical to the development of high-efficiency, low-emission and fuel-flexible combustion systems used for propulsion and power generation. Predicting the onset of dynamics remains a challenge because of the complex interactions among several multi-scale phenomena, including turbulence, kinetics and acoustics, and their strong dependence on the operating conditions and fuel properties. In this thesis, a series of experiments were conducted in a laboratory-scale combustor, burning lean premixed propane/hydrogen/air mixtures over a range of equivalence ratio, fuel composition and inlet temperature. Dynamic pressure and flame chemiluminescence measurements are used to determine macro-scale characteristics such as the frequency, limit cycle amplitude and dynamic flame shape. High-speed, high-resolution particle image velocimetry (PIV) is used to quantify the micro-scale structure of the flow, while planar laser-induced fluorescence (PLIF) of OH radical is used to investigate the flame microstructure. Results demonstrate that combustion dynamics in wake-stabilized flames can be characterized using a single non-dimensional parameter that collapses many response measures over a range of operating conditions and fuel composition, including the critical wake length at which dynamics is first observed, the critical phase at which transition among dynamic modes is encountered, and the limit cycle amplitude, emphasizing the role of the physics and chemistry of the flame processes in driving the overall system dynamics and encapsulating the governing mechanisms. The proposed parameter is based on the normalized strained flame consumption speed, which encapsulates the flow-combustion interactions at the flame scale. PIV data reveal significant changes in the recirculation zone structure depending on the equivalence ratio and the fuel composition, demonstrating the impact of chemical kinetics on the flow. These changes are shown to correlate strongly with the stability characteristics, i.e., blow-off and flashback limits as well as the onset of the thermoacoustic instabilities, highlighting a critical role of the recirculation zone in flame stabilization. An expression for the critical phase at which dynamic mode transition occurs is derived based on the linear acoustic energy balance. It is shown that the critical phase is also a function of the same non-dimensional parameter, suggesting that it represents the state within a dynamic mode as well. Results show that the normalized phase correlates with the upper- and lower-boundary of a dynamic mode, thus being a necessary and sufficient condition for dynamics. The results provide a metric for quantifying the instability margins of fuel-flexible combustors operating over a wide range of conditions. Analysis of PIV and OH-LIF data suggests that heat transfer near the flame-holder may play an important role in determining the stability characteristics. The impact of heat transfer on the onset of dynamics is experimentally investigated using different flame-holders. Results demonstrate the effectiveness of using heat-insulating materials as a passive control strategy to prevent or significantly delay the onset of the instabilities.

Large Eddy Simulations of Premixed Turbulent Flame Dynamics

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ISBN 13 :
Total Pages : 300 pages
Book Rating : 4.:/5 (92 download)

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Book Synopsis Large Eddy Simulations of Premixed Turbulent Flame Dynamics by : Gaurav Kewlani

Download or read book Large Eddy Simulations of Premixed Turbulent Flame Dynamics written by Gaurav Kewlani and published by . This book was released on 2014 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt: High efficiency, low emissions and stable operation over a wide range of conditions are some of the key requirements of modem-day combustors. To achieve these objectives, lean premixed flames are generally preferred as they achieve efficient and clean combustion. A drawback of lean premixed combustion, however, is that the flames are more prone to dynamics. The unsteady release of sensible heat and flow dilatation in combustion processes create pressure fluctuations which, particularly in premixed flames, can couple with the acoustics of the combustion system. This acoustic coupling creates a feedback loop with the heat release that can lead to severe thermoacoustic instabilities that can damage the combustor. Understanding these dynamics, predicting their onset and proposing passive and active control strategies are critical to large-scale implementation. For the numerical study of such systems, large eddy simulation (LES) techniques with appropriate combustion models and reaction mechanisms are highly appropriate. These approaches balance the computational complexity and predictive accuracy. This work, therefore, aims to explore the applicability of these methods to the study of premixed wake stabilized flames. Specifically, finite rate chemistry LES models that can effectively capture the interaction between different turbulent scales and the combustion fronts have been implemented, and applied for the analysis of premixed turbulent flame dynamics in laboratory-scale combustor configurations. Firstly, the artificial flame thickening approach, along with an appropriate reduced chemistry mechanism, is utilized for modeling turbulence-combustion interactions at small scales. A novel dynamic formulation is proposed that explicitly incorporates the influence of strain on flame wrinkling by solving a transport equation for the latter rather than using local-equilibrium-based algebraic models. Additionally, a multiple-step combustion chemistry mechanism is used for the simulations. Secondly, the presumed-PDF approach, coupled with the flamelet generated manifold (FGM) technique, is also implemented for modeling turbulence-combustion interactions. The proposed formulation explicitly incorporates the influence of strain via the scalar dissipation rate and can result in more accurate predictions especially for highly unsteady flame configurations. Specifically, the dissipation rate is incorporated as an additional coordinate to presume the PDF and strained flamelets are utilized to generate the chemistry databases. These LES solvers have been developed and applied for the analysis of reacting flows in several combustor configurations, i.e. triangular bluff body in a rectangular channel, backward facing step configuration, axi-symmetric bluff body in cylindrical chamber, and cylindrical sudden expansion with swirl, and their performance has been be validated against experimental observations. Subsequently, the impact of the equivalence ratio variation on flame-flow dynamics is studied for the swirl configuration using the experimental PIV data as well as the numerical LES code, following which dynamic mode decomposition of the flow field is performed. It is observed that increasing the equivalence ratio can appreciably influence the dominant flow features in the wake region, including the size and shape of the recirculation zone(s), as well as the flame dynamics. Specifically, varying the heat loading results in altering the dominant flame stabilization mechanism, thereby causing transitions across distinct- flame configurations, while also modifying the inner recirculation zone topology significantly. Additionally, the LES framework has also been applied to gain an insight into the combustion dynamics phenomena for the backward-facing step configuration. Apart from evaluating the influence of equivalence ratio on the combustion process for stable flames, the flame-flow interactions in acoustically forced scenarios are also analyzed using LES and dynamic mode decomposition (DMD). Specifically, numerical simulations are performed corresponding to a selfexcited combustion instability configuration as observed in the experiments, and it is observed that LES is able to suitably capture the flame dynamics. These insights highlight the effect of heat release variation on flame-flow interactions in wall-confined combustor configurations, which can significantly impact combustion stability in acoustically-coupled systems. The fidelity of the solvers in predicting the system response to variation in heat loading and to acoustic forcing suggests that the LES framework can be suitably applied for the analysis of flame dynamics as well as to understand the fundamental mechanisms responsible for combustion instability. KEY WORDS - large eddy simulation, LES, wake stabilized flame, turbulent premixed combustion, combustion modeling, artificially thickened flame model, triangular bluff body, backward facing step combustor, presumed-PDF model, flamelet generated manifold, axi-symmetric bluff body, cylindrical swirl combustor, particle image velocimetry, dynamic mode decomposition, combustion instability, forced response.

Turbulent Flame Microstructure, Dynamics, and Thermoacoustic Instability in Swirl-stabilized Premixed Combustion

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ISBN 13 :
Total Pages : 220 pages
Book Rating : 4.:/5 (913 download)

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Book Synopsis Turbulent Flame Microstructure, Dynamics, and Thermoacoustic Instability in Swirl-stabilized Premixed Combustion by : Zachary Alexander LaBry

Download or read book Turbulent Flame Microstructure, Dynamics, and Thermoacoustic Instability in Swirl-stabilized Premixed Combustion written by Zachary Alexander LaBry and published by . This book was released on 2015 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the most difficult challenges facing the development of modern gas turbines-for power generation, and propulsion-is the mitigation of dynamic instabilities in the presence of efficiency and emissions constraints. Dynamic instabilities-self-excited, self-sustaining oscillations which link the combustor acoustics to the combustion process-can result in significant levels of thermal and mechanical stress on combustion systems, leading to reduced operational lifetime, potentially dangerous failure modes, and significant deviations from the desired operating conditions. Due to the complexity of the problem, with the relevant time and length scales of the system--from the chemistry to the acoustics-spanning several orders of magnitude, even sophisticated numerical techniques have been severely limited in their ability to make reliable predictions, leaving the task of finding and eliminating modes of instability to a lengthy and expensive trial-and-error process. Lean-premixed combustion, one of the leading technologies for low emission combustors, is particularly susceptible to these types of instabilities. The sealed systems that are necessary to maintain a reaction in a lean mixture do not attenuate acoustics well, which often results in high-amplitude pressure fluctuations. In this thesis, we focus on developing a better predictive framework for the onset of combustion instabilities in a swirl-stabilized, lean-premixed combustor. We correlate the self-excited acoustic behavior with quantifiable system properties that can be generalized across different fuel blends. This work is predicated on the idea that self-excited combustion instability arises from the selective amplification of the noise inherent in a turbulent combustion system, and that the frequency-based response of the flame is a function of the flame geometry. In the first part of the thesis, we focus on the flame geometry, identifying several discrete transitions that take place in the swirl-stabilized flame as we adjust the equivalence ratio. By comparing the transitions across several CH4/H2 fuel blends, and using statistical techniques to interrogate the global effect of the small-scale flow-flame interactions, we find that the extinction strain rate-the flow-driven rate of change in flame surface area at which the chemistry is no longer -sufficiently fast to maintain the reaction-is directly linked to the flame transitions. The swirl-stabilized flow features several critical regions with large and unsteady velocity derivatives, particularly, a pair of shear layers that divide the incoming flow of reactants from an inner and an outer recirculation zone. As the extinction strain rate increases with increasing equivalence ratio, the flame transitions through these critical regions, manifesting as discrete changes in the flame geometry. In the second part, we address the correlation between self-excited instability and the forced acoustic response. By modifying the pressure boundary conditions, we decouple the flame from the acoustics over a domain of interest (defined by a range of equivalence ratios that correspond to the onset of dynamic instability in the coupled system). We then apply external acoustic forcing at a single frequency to ascertain the response of the flame to each particular forcing frequency by means of a flame transfer function. This enables us to consider the frequency-by-frequency response of the flame to its own internally generated noise. We show that the onset of instability is well-predicted by the overlap of the natural acoustic frequencies of the combustor (predicted using a non-linear flame response model) with those frequencies for which the phase of the flame transfer function satisfies the well-known Rayleigh criterion, which is a necessary condition for the presence of self-excited combustion instability. By examining both the forced response and the self-excited instability across several different fuel blends, we go on to show that both behaviors correlate well with the flame geometry, which we have already shown to be dictated by the extinction strain rate of the particular fuel blend. We go on to collapse both sets of data on the strained flame consumption speed taken at the limit of the extinction strain rate, and in doing so, present a framework for predicting the operating conditions under which the combustor in the coupled configuration will go unstable based on measurements and correlations from the uncoupled configuration. Furthermore by taking the consumption speed at the extinction limit, we are correlating the geometry and dynamics with a parameter that is solely a function of mixture properties. This provides the basis for a framework for predicting instability from properties that are more readily measured or simulated, and provides and explicit means of converting these results to different fuel mixtures.

Modeling and Simulation of Turbulent Combustion

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Publisher : Springer
ISBN 13 : 9811074100
Total Pages : 663 pages
Book Rating : 4.8/5 (11 download)

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Book Synopsis Modeling and Simulation of Turbulent Combustion by : Santanu De

Download or read book Modeling and Simulation of Turbulent Combustion written by Santanu De and published by Springer. This book was released on 2017-12-12 with total page 663 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents a comprehensive review of state-of-the-art models for turbulent combustion, with special emphasis on the theory, development and applications of combustion models in practical combustion systems. It simplifies the complex multi-scale and nonlinear interaction between chemistry and turbulence to allow a broader audience to understand the modeling and numerical simulations of turbulent combustion, which remains at the forefront of research due to its industrial relevance. Further, the book provides a holistic view by covering a diverse range of basic and advanced topics—from the fundamentals of turbulence–chemistry interactions, role of high-performance computing in combustion simulations, and optimization and reduction techniques for chemical kinetics, to state-of-the-art modeling strategies for turbulent premixed and nonpremixed combustion and their applications in engineering contexts.

Turbulent Combustion

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Publisher : Cambridge University Press
ISBN 13 : 1139428063
Total Pages : 322 pages
Book Rating : 4.1/5 (394 download)

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Book Synopsis Turbulent Combustion by : Norbert Peters

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.

Turbulent Combustion Modeling

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Publisher : Springer Science & Business Media
ISBN 13 : 9400704127
Total Pages : 496 pages
Book Rating : 4.4/5 (7 download)

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Book Synopsis Turbulent Combustion Modeling by : Tarek Echekki

Download or read book Turbulent Combustion Modeling written by Tarek Echekki and published by Springer Science & Business Media. This book was released on 2010-12-25 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent combustion sits at the interface of two important nonlinear, multiscale phenomena: chemistry and turbulence. Its study is extremely timely in view of the need to develop new combustion technologies in order to address challenges associated with climate change, energy source uncertainty, and air pollution. Despite the fact that modeling of turbulent combustion is a subject that has been researched for a number of years, its complexity implies that key issues are still eluding, and a theoretical description that is accurate enough to make turbulent combustion models rigorous and quantitative for industrial use is still lacking. In this book, prominent experts review most of the available approaches in modeling turbulent combustion, with particular focus on the exploding increase in computational resources that has allowed the simulation of increasingly detailed phenomena. The relevant algorithms are presented, the theoretical methods are explained, and various application examples are given. The book is intended for a relatively broad audience, including seasoned researchers and graduate students in engineering, applied mathematics and computational science, engine designers and computational fluid dynamics (CFD) practitioners, scientists at funding agencies, and anyone wishing to understand the state-of-the-art and the future directions of this scientifically challenging and practically important field.

Fundamentals of Turbulent and Multiphase Combustion

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Publisher : John Wiley & Sons
ISBN 13 : 111809929X
Total Pages : 914 pages
Book Rating : 4.1/5 (18 download)

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Book Synopsis Fundamentals of Turbulent and Multiphase Combustion by : Kenneth Kuan-yun Kuo

Download or read book Fundamentals of Turbulent and Multiphase Combustion written by Kenneth Kuan-yun Kuo and published by John Wiley & Sons. This book was released on 2012-07-03 with total page 914 pages. Available in PDF, EPUB and Kindle. Book excerpt: Detailed coverage of advanced combustion topics from the author of Principles of combustion, Second Edition Turbulence, turbulent combustion, and multiphase reacting flows have become major research topics in recent decades due to their application across diverse fields, including energy, environment, propulsion, transportation, industrial safety, and nanotechnology. Most of the knowledge accumulated from this research has never been published in book form—until now. Fundamentals of Turbulent and Multiphase Combustion presents up-to-date, integrated coverage of the fundamentals of turbulence, combustion, and multiphase phenomena along with useful experimental techniques, including non-intrusive, laser-based measurement techniques, providing a firm background in both contemporary and classical approaches. Beginning with two full chapters on laminar premixed and non-premixed flames, this book takes a multiphase approach, beginning with more common topics and moving on to higher-level applications. In addition, Fundamentals of Turbulent and Multiphase Combustion: Addresses seven basic topical areas in combustion and multiphase flows, including laminar premixed and non-premixed flames, theory of turbulence, turbulent premixed and non-premixed flames, and multiphase flows Covers spray atomization and combustion, solid-propellant combustion, homogeneous propellants, nitramines, reacting boundary-layer flows, single energetic particle combustion, and granular bed combustion Provides experimental setups and results whenever appropriate Supported with a large number of examples and problems as well as a solutions manual, Fundamentals of Turbulent and Multiphase Combustion is an important resource for professional engineers and researchers as well as graduate students in mechanical, chemical, and aerospace engineering.

Fundamentals of Premixed Turbulent Combustion

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Publisher : CRC Press
ISBN 13 : 1466510242
Total Pages : 551 pages
Book Rating : 4.4/5 (665 download)

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Book Synopsis Fundamentals of Premixed Turbulent Combustion by : Andrei Lipatnikov

Download or read book Fundamentals of Premixed Turbulent Combustion written by Andrei Lipatnikov and published by CRC Press. This book was released on 2012-10-24 with total page 551 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lean burning of premixed gases is considered to be a promising combustion technology for future clean and highly efficient gas turbine combustors. Yet researchers face several challenges in dealing with premixed turbulent combustion, from its nonlinear multiscale nature and the impact of local phenomena to the multitude of competing models. Filling a gap in the literature, Fundamentals of Premixed Turbulent Combustion introduces the state of the art of premixed turbulent combustion in an accessible manner for newcomers and experienced researchers alike. To more deeply consider current research issues, the book focuses on the physical mechanisms and phenomenology of premixed flames, with a brief discussion of recent advances in partially premixed turbulent combustion. It begins with a summary of the relevant knowledge needed from disciplines such as thermodynamics, chemical kinetics, molecular transport processes, and fluid dynamics. The book then presents experimental data on the general appearance of premixed turbulent flames and details the physical mechanisms that could affect the flame behavior. It also examines the physical and numerical models for predicting the key features of premixed turbulent combustion. Emphasizing critical analysis, the book compares competing concepts and viewpoints with one another and with the available experimental data, outlining the advantages and disadvantages of each approach. In addition, it discusses recent advances and highlights unresolved issues. Written by a leading expert in the field, this book provides a valuable overview of the physics of premixed turbulent combustion. Combining simplicity and topicality, it helps researchers orient themselves in the contemporary literature and guides them in selecting the best research tools for their work.

High-fidelity Computation and Modeling of Turbulent Premixed Combustion

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Publisher :
ISBN 13 :
Total Pages : 169 pages
Book Rating : 4.:/5 (128 download)

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Book Synopsis High-fidelity Computation and Modeling of Turbulent Premixed Combustion by : Yunde Su

Download or read book High-fidelity Computation and Modeling of Turbulent Premixed Combustion written by Yunde Su and published by . This book was released on 2020 with total page 169 pages. Available in PDF, EPUB and Kindle. Book excerpt: High-fidelity simulation of turbulent premixed combustion is desirable for the design of advanced energy-efficient and environmentally-friendly combustion engines. An attractive high-fidelity simulation approach that is applicable to practical combustion problems is the large eddy simulation (LES), in which the large-scale dynamics of flame-turbulence interaction are resolved down to a filter scale while the sub-filter phenomena are modeled. Since the grid size in practical LES is typically comparable to or larger than the flame front thickness, the filtered flame front is not well resolved when the filter size is taken as the grid size. Under such a condition, the spurious propagation of the filtered flame front can occur. To overcome this challenge, the front propagation formulation (FPF) method that was originally proposed to simulate propagating reaction fronts on under-resolved grids is extended to LES of turbulent premixed combustion. The closure of the regularized Dirac delta function, which FPF uses to minimize the spurious propagation, is investigated using direct numerical simulation (DNS) data for statistically planar premixed flames propagating in homogeneous isotropic turbulence. As a key ingredient in the sub-filter flame speed model that is required for the FPF method and many other combustion models, the flame wrinkling in the DNS dataset is studied in the context of fractals. The results show that, for the flames investigated in the DNS, the fractal dimension increases with the Reynolds number and the inner cut-off scale is on the order of the flame thickness. The FPF-LES framework is validated for a non-piloted Bunsen flame in the corrugated flamelet regime and a piloted Bunsen flame in the thin reaction zone regime. In both cases, the predicted results compare reasonably well with experimental measurements, demonstrating the performance of the FPF-LES framework. In LES of the non-piloted Bunsen flame, it is found that neglecting the stretch effects can cause the flame length and radius to be clearly under-predicted, which suggests the necessity to include stretch effects in LES. It is also found that the strain rate in the stretch effect model needs to be evaluated on the unburned side of the filtered flame to avoid the artificial modification of the flame wrinkling. Finally, the FPF-LES framework is applied to an experimentally studied spark-ignition (SI) engine with the emphasis on the prediction of cycle-to-cycle variations (CCVs), which are known to limit engine performance. To capture the degree of CCVs observed in the experiments, a laminar-to-turbulent flame transition model that describes the non-equilibrium sub-filter flame speed evolution during an early stage of flame kernel growth is developed. The multi-cycle LES with the proposed flame transition model under the FPF framework is found to reproduce experimentally-observed CCVs satisfactorily. The simulation results indicate the importance of modeling the laminar-to-turbulent flame transition and the effect of turbulence on the transition process, when predicting CCVs, under certain engine conditions.

Heat Release and Flame Scale Effects on Turbulence Dynamics in Confined Premixed Flows

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ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (138 download)

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Book Synopsis Heat Release and Flame Scale Effects on Turbulence Dynamics in Confined Premixed Flows by : Max Fortin

Download or read book Heat Release and Flame Scale Effects on Turbulence Dynamics in Confined Premixed Flows written by Max Fortin and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: As industry transitions to a net-zero carbon future, turbulent premixed combustion will remain an integral process for power generating gas turbines and are also desired for aviation engines due to their ability to minimize pollutant emissions. However, accurately predicting the behavior of a turbulent reacting flow field remains a challenge. To better understand the dynamics of premixed reacting flows, this study experimentally investigates the evolution of turbulence in a high-speed bluff-body combustor. The combustor is operated across a range of equivalence ratios from 0.7-1 to quantify the role of heat release and flame scales on the evolution of turbulence as the flow evolves from reactants to products. High-speed particle image velocimetry and CH* chemiluminescence imaging systems are simultaneously employed to quantify turbulent flame and flow dynamics. The results demonstrate that the flame augments turbulence fluctuations as the flow evolves from reactants to products for all cases. However, turbulence fluctuations increase monotonically with the heat of combustion and corresponding turbulent flame speed. Nondimensional spatial profiles of turbulence are used to develop a correlation to predict the increase in turbulent fluctuations in an extended progress variable space. A Reynolds Averaged Navier Stokes (RANS) decomposition is also explored to better characterize the effects of heat release on turbulence evolution dynamics. The correlations and RANS decomposition can guide modeling capabilities to better predict confined turbulent reacting flows and accelerate design strategies for premixed turbines with carbon-free fuels.

Lean Premixed Flame Structure in Intense Turbulence

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Publisher :
ISBN 13 :
Total Pages : 364 pages
Book Rating : 4.:/5 (55 download)

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Book Synopsis Lean Premixed Flame Structure in Intense Turbulence by : Sastri Purushottama Nandula

Download or read book Lean Premixed Flame Structure in Intense Turbulence written by Sastri Purushottama Nandula and published by . This book was released on 2003 with total page 364 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Turbulent Combustion

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ISBN 13 :
Total Pages : 536 pages
Book Rating : 4.0/5 ( download)

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Book Synopsis Turbulent Combustion by : L. Vervisch

Download or read book Turbulent Combustion written by L. Vervisch and published by . This book was released on 2005 with total page 536 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Premixed Turbulent Combustion Flowfield Measurements Using PIV and LST and Their Application to Flamelet Modelling of Engine Combustion

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Publisher :
ISBN 13 :
Total Pages : 12 pages
Book Rating : 4.:/5 (565 download)

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Book Synopsis Premixed Turbulent Combustion Flowfield Measurements Using PIV and LST and Their Application to Flamelet Modelling of Engine Combustion by : Neil W. H. Armstrong

Download or read book Premixed Turbulent Combustion Flowfield Measurements Using PIV and LST and Their Application to Flamelet Modelling of Engine Combustion written by Neil W. H. Armstrong and published by . This book was released on 1992 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Phase-resolved Characterization of Conical Turbulent Premixed Flames

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Publisher :
ISBN 13 :
Total Pages : 232 pages
Book Rating : 4.:/5 (81 download)

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Book Synopsis Phase-resolved Characterization of Conical Turbulent Premixed Flames by : Sayan Biswas

Download or read book Phase-resolved Characterization of Conical Turbulent Premixed Flames written by Sayan Biswas and published by . This book was released on 2012 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Effect of Harmonic Forcing on Turbulent Flame Properties

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Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (74 download)

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Book Synopsis Effect of Harmonic Forcing on Turbulent Flame Properties by : Sai Kumar Thumuluru

Download or read book Effect of Harmonic Forcing on Turbulent Flame Properties written by Sai Kumar Thumuluru and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Lean premixed combustors are highly susceptible to combustion instabilities, caused by the coupling between heat release fluctuations and combustor acoustics. In order to predict the conditions under which these instabilities occur and their limit cycle amplitudes, understanding of the amplitude dependent response of the flame to acoustic excitation is required. Extensive maps of the flame response were obtained as a function of perturbation amplitude, frequency, and flow velocity. These maps illustrated substantial nonlinearity in the perturbation velocity - heat release relationship, with complex topological dependencies that illustrate folds and kinks when plotted in frequency-amplitude-heat release space. A detailed analysis of phase locked OH PLIF images of acoustically excited swirl flames was used to identify the key controlling physical processes and qualitatively discuss their characteristics. The results illustrate that the flame response is not controlled by any single physical process but rather by several simultaneously occurring processes which are potentially competing, and whose relative significance depends upon forcing frequency, amplitude of excitation, and flame stabilization dynamics. An in-depth study on the effect of acoustic forcing on the turbulent flame properties was conducted in a turbulent Bunsen flame using PIV measurements. The results showed that the flame brush thickness and the local consumption speed were modulated in the presence of acoustic forcing. These results will not only be a useful input to help improve combustion dynamics predictions but will also help serve as validation data for models.

Dominant Interscale Dynamics in Premixed Turbulent Combustion for Application to Large-Eddy Simulation

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ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (125 download)

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Book Synopsis Dominant Interscale Dynamics in Premixed Turbulent Combustion for Application to Large-Eddy Simulation by : Yash Girish Shah

Download or read book Dominant Interscale Dynamics in Premixed Turbulent Combustion for Application to Large-Eddy Simulation written by Yash Girish Shah and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The large-eddy simulation (LES) approach has become an important tool for engineering design and optimization of combustion devices. In a properly designed LES, the larger-scale flow variations are resolved by the effective numerical grid, which incorporates the implicit/explicit filtering introduced by the spatial filtering from the grid, artificial diffusion from numerical schemes, and modeled terms. The dynamical consequences of the remaining subfilter-scale (SFS) fluctuations below the effective grid to the evolution of grid-resolved scales (RS) motions in dynamically relevant physical variables are modeled. The nonlinearities in the dynamical evolution of resolved-scale variables that result from the inherent nonlinear coupling between the resolved and subfilter scales are often not sufficiently well captured in turbulent combustion, as the intermediate species that participate in the heat release process are dominantly only at chemical length and time scales well within the subfilter scales. In this research work, we explore new LES modeling strategies that represent the RS-SFS interactions in the evolution of RS primary variables (momentum, energy and species concentrations) more directly by approximating the SFS content that contributes dominantly to the dynamical evolution of RS quantities using simple mathematical forms. To achieve this, we first obtain a highly resolved three-dimensional Direct Numerical Simulation (DNS) dataset of flame-turbulence interactions that capture the essential RS-SFS interactions in primary variables over a wide range of scales. To systematically analyze the RS-SFS interscale couplings for LES, we then obtain the scale content as the Fourier space representation of the inherently inhomogeneous DNS dataset by applying a discontinuity removal procedure that removes the unphysical gradients naturally introduced at the boundaries of the computational domain by the periodic extension that occurs with the Fourier transform over a bounded domain. The Fourier space representation of primary variables in turbulence-flame dynamical interactions are systematically analyzed. Variables that display high gradients across the flame front over length scales comparable to or larger than flame scales are found to have higher Fourier variance contributions at wavenumbers below flame scale wavenumber, while Fourier variance contributions from variables that are localized only within the flame are found to be distributed to higher wavenumbers in Fourier space. Using this Fourier space representation, we systematically determine the scales of the energy-dominant flow variations in momentum and enthalpy that are resolved by LES and objectively identify the RS and SFS fluctuations for other primary variables. Variables that display frontal variations surrounding the flame are found to be dominantly resolved while those variables that are localized only within the flame are found to be dominantly subfilter scale. These differences in Fourier variance distributions are shown to have implications to the extent of RS-SFS interactions between these variables. We take advantage of the mathematical property of the Fourier spectral description that allows the nonlinearities from the advective transport and chemical reaction rates in the dynamical system to be expressed as elemental sums over triadic interactions involving three wavevectors and quadrad interactions involving four wavevectors between the RS and SFS fluctuations. Using this elemental representation, the SFS content that contributes dominantly to the dynamical evolution of resolved-scales advective nonlinearity is identified by applying the triads downselection procedure [75]. We find that RS-SFS interactions involving SFS content from significantly larger scales compared to the smallest resolvable scales in the DNS are required to adequately estimate the resolved-scale advective nonlinearity in LES. These dynamically dominant SFS for RS advective nonlinearity span over a broader range of wavenumbers for dominantly SFS variables compared to variables that are dominantly resolved-scale. To study the dominant RS-SFS interactions in the chemical nonlinearity, a new two-stage downselection procedure is developed in this work, which expresses the quadrad interactions between the reaction rate constant and the species concentrations to the resolved chemical reaction rates first into triadic interactions between the chemical reaction rate constant and the product of species concentrations. The product of species concentrations is then expressed as a triadic sum over interactions between individual species concentrations and the corresponding dynamically dominant SFS is extracted from both stages using triad downselect procedure for second-order nonlinearities. The dynamically dominant SFS resulting from this procedure is found to be considerably reduced from the full SFS and is shown to be effective in adequately approximating the chemical reaction rates at resolved scales through RS-SFS interactions. The structure underlying the distribution of these dynamically dominant SFS fluctuations in species concentrations are identified for key species in representative reactions in regions where the incorporation of the SFS content is impactful to the estimation of chemical reaction rates in LES. The dynamically dominant SFS species structure is found in two groupings: ``single-banded'' structure characterized by one distinct peak, and ``double-banded'' structure characterized by two peaks of opposite signs. Species that are produced and consumed within the flame are observed to have single-banded structure and species displaying a frontal behavior are observed to have double-banded structure in their dynamically dominant SFS concentrations on average. The local structure of the dynamically dominant SFS species concentrations surrounding the flame is impacted by neighboring flame-flame interactions as well as by variations in flame curvature. The impacts of the flame-flame interactions are strong when the dynamically dominant SFS species structure has ``large'' length scales with concentration peaks significantly displaced from the flame front. Finally, mathematical forms to approximate the mean single and double banded structure in the dynamically dominant SFS concentrations are proposed for application within a structure-based SFS modeling strategy which directly embeds the interaction between the modeled dominant SFS content and the RS evolution within existing LES frameworks. This research lays the groundwork for future LES model developments that utilize this strategy for improving LES predictions of resolved-scale dynamics.

Large-eddy Simulation of Premixed Turbulent Combustion Using Flame Surface Density Approach

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Book Synopsis Large-eddy Simulation of Premixed Turbulent Combustion Using Flame Surface Density Approach by : Wen Lin

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