| 1. |
- Hodzic, Erdzan, et al.
(author)
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A Large Eddy Simulation Study of Bluff Body Flame Dynamics Approaching Blow-Off
- 2017
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In: Combustion Science and Technology. - : Taylor & Francis. - 0010-2202 .- 1563-521X. ; 189:7, s. 1107-1137
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Journal article (peer-reviewed)abstract
- The mechanisms leading to blowoff were investigated numerically by analyzing bluff body stabilized flame at two conditions: a condition far from blowoff to a condition just prior to blowoff. Large eddy simulations have been used to capture the time dependent, three-dimensional evolution of the field. The results were first validated to available experimental data, showing very good agreement for the flow and overall good agreement for the flame. Changes in the large-scale structures are investigated by means of proper orthogonal decomposition and the wavelet method, elucidating the underlying dynamics of the complex flow-flame interaction of a flame approaching blowoff. Our results reveal that, when the flame approaches blowoff conditions, significant changes are found in the large-scale structures responsible for entrainment of species into the recirculation zone located downstream of the bluff body. Possible causes of this shift in large-scale structures are also discussed, which may be useful for extending the blowoff limits of bluff body stabilized burners.
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| 2. |
- Hodzic, Erdzan
(author)
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Analysis of flow dynamics and flame stabilization in gas turbine related combustors
- 2016
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Doctoral thesis (other academic/artistic)abstract
- The regulations on the emissions from combustion devices are getting more and more strict for environmental and human health reasons. Modern combustion research faces two major challenges; reduction of the pollutants, such as CO, NOx and unburnt hydro- carbons and increase of the combustion efficiency. Current trend for stationary power generation is to use lean premixed and/or pre-vaporized combustors, close to blow-off limit. Besides the beneficial effects of lower emissions and improved performance, the use of lean, near blow-off combustion gives rise to combustion instabilities that can lead to flashback, blow-off as well as acoustical and mechanical vibrations. A clear under- standing of the dynamics of the flame and the flow under lean conditions has not been reached yet. This is where the contributions of this thesis lie. In this work, advanced techniques, namely, Reynolds Averaged Navier Stokes (RANS) based models, Large Eddy Simulation (LES) models, Proper Orthogonal Decomposition (POD), Dynamic Mode Decomposition (DMD) and wavelet-analysis have been applied to analyze both stable and unstable lean flames.Maintaining stable flame is difficult when the flame speed of any practical fuel is several orders of magnitude smaller than the flow velocity and a flame holding mechanism is required. Stabilization may be achieved primarily by swirl or jet induced recirculating flow or by a bluff-body flame holder. Bluff-bodies as flame-holders are found in a wide range of high-speed reacting environments, e.g. ram-jets, scram-jets and turbojet after- burners. Primary goals of this study were to examine in detail the possibility of modeling a flame close to blow-off and during the blow-off, and furthermore to extract the dynamics of a bluff body flame under stable flame and close to blow-off conditions. In the end, based on the LES results, some of the modern theories of bluff-body flames approaching blow-off were critically assessed. The findings were summarized and a hypothesis on the full sequence of events leading to blow-off was proposed.Real gas turbine combustors are typically characterized by much more complex geometries than bluff-bodies. Apart from stability issues, operation flexibility, efficiency and fuel flexibility need also to be addressed, especially when dealing with alternative fuel gas mixtures. One of the purposes of this work was also to design a burner that can, experimentally and numerically address some of these issues. The burner should be similar to a modern gas turbine burners, downscaled and experimentally feasible, yet possessing all of the complex interactions between fundamental combustion phenomenon and fluid mechanics of an industrial gas turbine combustor. This was done by using advanced computational tools in conjunction with CAD tools for identifying the operating limits of such a burner. Further, several experimental set-ups were re-designed for operation under various conditions.Throughout the thesis, LES-based models showed capabilities of predicting flames under stable and unstable conditions. RANS-based models were proved to be useful for design purposes. It was shown how POD, DMD and wavelets can be used for not just identifying important flame-flow features but also exploring the flow-flame interaction.
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| 3. |
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| 4. |
- Hodzic, Erdzan, et al.
(author)
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Large Eddy Simulation of Bluff-Body Flame Approaching Blow-Off : A Sensitivity Study
- 2019
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In: Combustion Science and Technology. - : TAYLOR & FRANCIS INC. - 0010-2202 .- 1563-521X. ; 191:10, s. 1815-1842
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Journal article (peer-reviewed)abstract
- As almost all combustion processes of practical interest take place in the presence of turbulence, the development of the increasingly refined turbulence-chemistry interaction (TCI) models has led to highly sophisticated approaches. Nearly all of the studies comparing different models focus on stable premixed/non-premixed flame configurations. In this work, the focus is on well-documented, lean premixed bluff-body stabilized flames approaching blow-off and on the blow-off sequence itself. Large Eddy Simulations (LES) have been used to capture the time-dependent, three-dimensional flow-field using Transported Probability Density Function (TPDF), Partially Stirred Reactor Model (PaSR), and Implicit LES (ILES) models. Furthermore, the influence of finite-rate chemistry and different chemical mechanisms is evaluated to determine the limitation and capability of the different TCI approaches for modeling flames just prior to and during the transient blow-off process. While the average flow-fields do not reveal any significant differences between modeling approaches, detailed analysis of the flame reveals that there are differences in the predicted flame thickness and composition. The ability of the considered TCI models to predict local as well as full-flame extinction during the blow-off is investigated as well. It is demonstrated that such a blow-off sequence is not always governed by complex chemistry.
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| 5. |
- Hodzic, Erdzan, et al.
(author)
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Large eddy simulation of bluff body flames close to blow-off using an Eulerian stochastic field method
- 2017
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In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 181, s. 1-15
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Journal article (peer-reviewed)abstract
- This paper reports on Large Eddy Simulation (LES) of turbulent premixed methane/air flames approaching blow-off. The study focuses on a stable flame, and on a flame just prior to blow-off, both stabilized by the Cambridge bluff-body burner. For turbulence-chemistry interaction, a model based on transported probability density function (TPDF) in conjunction with Eulerian stochastic fields is used. Velocity, species-concentration and heat release fields were first compared against experimental data showing good agreement. The results demonstrate that simulations of such complex combustion phenomena are possible and that the model is capable of reproducing the flame and the flow characteristics under both stable and close to blow-off conditions. A blow-off sequence was then examined and the results were used to evaluate some of the theories and mechanisms responsible for flame blow-off. It was found that the local extinction in the shear-layers had only minor impact on the flame blowing off and that the blow-off is a result of a series of events starting with the flame migrating into the recirculation zone. In the end, a mechanistic explanation is proposed for this series of events leading to full extinction of the flame.
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| 6. |
- Hodzic, Erdzan, et al.
(author)
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Large Eddy Simulation of lean blow off
- 2013
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In: [Host publication title missing]. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
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Conference paper (other academic/artistic)
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| 7. |
- Hodzic, Erdzan, et al.
(author)
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Numerical and experimental investigation of the cecost swirl burner
- 2018
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In: ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition : Combustion, Fuels, and Emissions - Combustion, Fuels, and Emissions. - 9780791851050 ; 4A
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Conference paper (peer-reviewed)abstract
- Clean technology has become a key feature due to increasing environmental concerns. Swirling flows, being directly associated with combustion performance and hence minimized pollutant formation, are encountered in most propulsion and power-generation combustion devices. In this study, the development process of the conceptual swirl burner developed at the Swedish National Centre for Combustion and Technology (CeCOST), is presented. Utilizing extensive computational fluid dynamics (CFD) analysis, both the lead time and cost in manufacturing of the different burner parts were significantly reduced. The performance maps bounded by the flashback and blow-off limits for the current configuration were obtained and studied in detail using advanced experimental measurements and numerical simulations. Utilizing high speed OH-chemiluminescence, OH/CH2O-PLIF and Large Eddy Simulation (LES), details of the combustion process and flame-flow interaction are presented. The main focus is on three different cases, a stable case, a case close to blow-off and flashback condition. We show the influence of the flame on the core flow and how an increase in swirl may extend the stability limit of the anchored flame in swirling flow burners.
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| 8. |
- Yu, Rixin, et al.
(author)
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Parametric learning of time-advancement operators for unstable flame evolution
- 2024
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In: Physics of Fluids. - 1070-6631. ; 36:4
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Journal article (peer-reviewed)abstract
- This study investigates the application of machine learning, specifically Fourier neural operator (FNO) and convolutional neural network (CNN), to learn time-advancement operators for parametric partial differential equations (PDEs). Our focus is on extending existing operator learning methods to handle additional inputs representing PDE parameters. The goal is to create a unified learning approach that accurately predicts short-term solutions and provides robust long-term statistics under diverse parameter conditions, facilitating computational cost savings and accelerating development in engineering simulations. We develop and compare parametric learning methods based on FNO and CNN, evaluating their effectiveness in learning parametric-dependent solution time-advancement operators for one-dimensional PDEs and realistic flame front evolution data obtained from direct numerical simulations of the Navier-Stokes equations.
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| 9. |
- Yu, Rixin, et al.
(author)
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Parametric learning of time-advancement operators for unstable flame evolution
- 2024
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In: Physics of fluids. - : American Institute of Physics. - 1070-6631 .- 1089-7666. ; 36:4
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Journal article (peer-reviewed)abstract
- This study investigates the application of machine learning, specifically Fourier neural operator (FNO) and convolutional neural network (CNN), to learn time-advancement operators for parametric partial differential equations (PDEs). Our focus is on extending existing operator learning methods to handle additional inputs representing PDE parameters. The goal is to create a unified learning approach that accurately predicts short-term solutions and provides robust long-term statistics under diverse parameter conditions, facilitating computational cost savings and accelerating development in engineering simulations. We develop and compare parametric learning methods based on FNO and CNN, evaluating their effectiveness in learning parametric-dependent solution time-advancement operators for one-dimensional PDEs and realistic flame front evolution data obtained from direct numerical simulations of the Navier-Stokes equations.
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