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.

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.

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.

Download or read book Turbulent Premixed Flames written by Nedunchezhian Swaminathan and published by Cambridge University Press. This book was released on 2011-04-25 with total page 447 pages. Available in PDF, EPUB and Kindle. Book excerpt: A work on turbulent premixed combustion is important because of increased concern about the environmental impact of combustion and the search for new combustion concepts and technologies. An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts. Lean premixed flames have the potential to offer ultra-low emission levels, but they are notoriously susceptible to combustion oscillations. Thus, sophisticated control measures are inevitably required. The editors' intent is to set out the modeling aspects in the field of turbulent premixed combustion. Good progress has been made on this topic, and this cohesive volume contains contributions from international experts on various subtopics of the lean premixed flame problem.

Download or read book Scaling and Efficiency of PRISM in Adaptive Simulations of Turbulent Premixed Flames written by and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The dominant computational cost in modeling turbulent combustion phenomena numerically with high fidelity chemical mechanisms is the time required to solve the ordinary differential equations associated with chemical kinetics. One approach to reducing that computational cost is to develop an inexpensive surrogate model that accurately represents evolution of chemical kinetics. One such approach, PRISM, develops a polynomial representation of the chemistry evolution in a local region of chemical composition space. This representation is then stored for later use. As the computation proceeds, the chemistry evolution for other points within the same region are computed by evaluating these polynomials instead of calling an ordinary differential equation solver. If initial data for advancing the chemistry is encountered that is not in any region for which a polynomial is defined, the methodology dynamically samples that region and constructs a new representation for that region. The utility of this approach is determined by the size of the regions over which the representation provides a good approximation to the kinetics and the number of these regions that are necessary to model the subset of composition space that is active during a simulation. In this paper, we assess the PRISM methodology in the context of a turbulent premixed flame in two dimensions. We consider a range of turbulent intensities ranging from weak turbulence that has little effect on the flame to strong turbulence that tears pockets of burning fluid from the main flame. For each case, we explore a range of sizes for the local regions and determine the scaling behavior as a function of region size and turbulent intensity.

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.

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.

Download or read book Micro mixing in Turbulent Premixed Flames written by Michael Joseph Kuron and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Accurate turbulent combustion models are key to establishing a predictive capability for combustion simulations at the device level. The transported probability density function (TPDF) methods provide an elegant solution to the challenge of closing the mean chemical source term in turbulent combustion modelling as it appears in closed form in the TPDF equations and thus the turbulence-chemistry interaction can be solved for without aggressive assumptions. This is crucial for predicting low temperature combustion, turbulent flames with the presence of local limit phenomena, and pollutant emissions. Despite some reported success in the literature, challenges remain when applying the TPDF method to turbulent premixed flames as the molecular mixing or micro-mixing term is unclosed, the modeling of which is considered to be a primary challenge. The objective of this dissertation is to evaluate the application of existing mixing models to turbulent premixed flames and to create high-fidelity scalar dissipation rate models to predict turbulent premixed combustion. In this dissertation, direct numerical simulation (DNS) data is utilized at each stage to obtain statistical information on the scalar dissipation rate and mixing timescales for turbulent premixed flames. In the first step, DNS of a temporally evolving premixed flame is used as a numerical test bed to evaluate commonly used mixing models in the context of turbulent premixed flames. This study demonstrates that the Euclidean Minimum Spanning Tree (EMST) model is capable of predicting the behavior of a turbulent premixed flame assuming that an accurate model for the scalar mixing rate, and thus the scalar dissipation rate, can be provided. In the next stage of the dissertation, chemical explosive mode analysis (CEMA) and DNS data with realistic chemistry are used to identify physiochemical processes that govern the conditional scalar dissipation rate behavior in a turbulent premixed flame and evaluate mixing timescales. A local Damköhler number is defined based on the CEMA results and four flame zones are identified. It is found that large fluctuations in the instantaneous scalar dissipation rate occur in the explosive zone, where the local Damköhler number is much larger than unity. Two mechanisms are identified to account for the large degree of scatter in the explosive zone: flame-flame interactions and flame-assisted ignition. A model for the Favre-averaged scalar dissipation rate is subsequently developed based on the insight gleaned from the DNS analysis. The new hybrid mixing rate model is developed to account for the scalar mixing rate behavior in both the turbulent mixing limit and the flamelet limit. The new hybrid timescale model is notable for its treatment of the flamelet mixing limit, an area where existing timescale models do not properly recover the correct mixing behavior. Comparisons to the DNS are performed with both a priori and a postereori comparisons, with the new hybrid model performing exceptionally well. Finally, in the last stage of the dissertation, a transport equation for the conditional scalar dissipation rate of a reactive scalar is derived and an order of magnitude analysis is performed to evaluate the importance of each term in the governing equation. The order of magnitude analysis is verified with the DNS data of turbulent premixed flames and an equation of the leading order terms is identified. Models for the unclosed terms in the leading order equation are developed and evaluated with DNS data, and a modelled equation for the conditional scalar dissipation rate is proposed. The modelled equation is then compared to the DNS data, and excellent agreement between the new model and the DNS is observed.

Download or read book Turbulent Combustion Modeling written by Tarek Echekki and published by Springer. This book was released on 2011-04-09 with total page 490 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.

Download or read book Numerical Simulations of Turbulent Combustion written by Andrei Lipatnikov and published by Mdpi AG. This book was released on 2020-07 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent burning of gaseous fuels is widely used for energy conversion in stationary power generation, e.g., gas turbines, land transportation, piston engines, and aviation, and aero-engine afterburners. Nevertheless, our fundamental understanding of turbulent combustion is still limited, because it is a highly non-linear and multiscale process that involves various local phenomena and thousands (e.g., for gasoline-air mixtures) of chemical reactions between hundreds of species, including several reactions that control emissions from flames. Therefore, there is a strong need for elaborating high fidelity, advanced numerical models, and methods that will catch the governing physical mechanisms of flame-turbulence interaction and, consequently, will make turbulent combustion computations an efficient predictive tool for applied research and, in particular, for development of a new generation of ultra-clean and highly efficient internal combustion engines that will allow society to properly respond to current environmental and efficiency challenges. Accordingly, papers published in this Special Issue (i) contribute to our fundamental understanding of flame-turbulence interaction by analyzing results of unsteady multi-dimensional numerical simulations and (ii) develop and validate high-fidelity models and efficient numerical methods for computational fluid Dynamics research into turbulent combustion in laboratory burners and engines.

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.

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.

Download or read book Simulation of Lean Premixed Turbulent Combustion written by Robert K. Cheng and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: There is considerable technological interest in developingnew fuel-flexible combustion systems that can burn fuels such ashydrogenor syngas. Lean premixed systems have the potential to burn thesetypes of fuels with high efficiency and low NOx emissions due to reducedburnt gas temperatures. Although traditional scientific approaches basedon theory and laboratory experiment have played essential roles indeveloping our current understanding of premixed combustion, they areunable to meet the challenges of designing fuel-flexible lean premixedcombustion devices. Computation, with itsability to deal with complexityand its unlimited access to data, hasthe potential for addressing thesechallenges. Realizing this potential requires the ability to perform highfidelity simulations of turbulent lean premixed flames under realisticconditions. In this paper, we examine the specialized mathematicalstructure of these combustion problems and discuss simulation approachesthat exploit this structure. Using these ideas we can dramatically reducecomputational cost, making it possible to perform high-fidelitysimulations of realistic flames. We illustrate this methodology byconsidering ultra-lean hydrogen flames and discuss how this type ofsimulation is changing the way researchers study combustion.

Download or read book Emission Modeling in Turbulent Premixed Flames written by Hongtao Yang and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent lean premixed combustion now plays a predominant role in reducing emission of pollutants such as NOx. For turbulent premixed flames located in the thin-reaction-zones regime, small-scale eddies could penetrate into the preheat zone of the flames and enhance the mixing process. In this study, the effects of small-scale turbulence on emission (NOx and CO) formation in premixed flame fronts are investigated through the incorporation of turbulence induced diffusion in the preheat zone of one-dimensional premixed flames. One-dimensional methane/air premixed flames are simulated with the 53-species GRI-Mech 3.0 mechanism at both atmospheric and engine conditions with different turbulence intensities. It is found that the NO generated in flame fronts deceases with increasing intensity of small-scale turbulence and the effect is more profound at high pressures. At high pressures, the turbulence induced diffusion in the preheat zone can reduce the NOx formation in flame fronts by more than 40%. On the other hand, the CO mass fraction in flame fronts increases with increasing intensity of small-scale turbulence. In the cases considered, the CO mass fraction in the flame fronts can increase by more than 55%. In addition, a flamelet-based approach that accounts for the flame thickening effects has been formulated to simulate NOx and CO formation in turbulent lean premixed combustion. In this approach, the species NO and CO are transported and solved in a simulation with chemical source terms being pre-calculated from 1-D premixed flames with detailed chemical kinetics and turbulence induced diffusion. The NO source term can be quantified by its formation in flame fronts and its formation rate in post-flame region. The CO source term can be calculated through its mass fraction at flame fronts, its mass fraction in the post-flame region and an oxidation time scale. The effect of heat loss on NO formation has been studied by investigate the relation between post-flame NO formation rate and flame temperature. Meanwhile, the effect of turbulent-chemistry interaction on NO were studied. The flamelet-based emission model has been implemented into Fluent and 3-Dimensional simulations were conducted in a combustion rig.

Download or read book A Framework for Turbulent Non premixed Combustion Modeling in OpenFoam written by Vasu Jaganath and published by . This book was released on 2020 with total page 143 pages. Available in PDF, EPUB and Kindle. Book excerpt: Combustion remains a critical technology for electricity generation, heating, transportation and other industrial processes. Turbulent combustion lies at the heart of many of these processes. The accurate, robust and efficient computational modeling of turbulent combustion is necessary to design clean, efficient and safe combustion devices and processes. For practical combustion problems the direct numerical simulation (DNS) of the governing equations is computationally intractable. The Reynolds averaged Navier-Stokes simulation (RANS) and large eddy simulation (LES) techniques have emerged as powerful tools to simulate turbulent reacting flows. RANS and LES methodologies require closure of the unclosed terms arising from the averaging or filtering the governing equations. Even with adequate closure, RANS and LES remain computationally infeasible for simulating many combustion processes in engineering applications, further simplifications regarding flame thickness, flow and chemical reaction time scales are required. The high Damk\"{o}hler (Da) number flames can be modeled using a reduced chemistry model. A flamelet derived reduced chemistry model like Flamelet Generated Manifolds (FGM) accounts for finite rate chemistry while it greatly simplifies the simulation of turbulent combustion as it decouples the turbulent transport and flame structure. The interaction between the turbulence and the flame front in non-premixed combustion is described by the probability density function (PDF) of the composition variables. In this work, a framework for turbulent combustion modeling is presented for both RANS and, LES with FGM reduced chemistry model. This framework consists of implementation of presumed and transported PDF models and is developed within the open source CFD software OpenFOAM. The simulation of the well-known piloted methane-air jet flames (Sandia flames) is conducted in RANS context with both presumed and transported PDF models. An "A priori" analysis is conducted based on the RANS/TPDF simulation data. The analysis quantifies the extent of errors in PPDF models, specifically errors in choice of presumed PDF, statistical independence and the number moments and cross moments considered. A new PPDF model based on the Gaussian copula approach for correlation of the composition variables is developed and analyzed. The implementation of RANS/TPDF solver incorporates robust algorithms for particle tracking, position and number control. The LES/TFDF simulation of Sandia flame D is conducted to showcase the capability of the developed framework.

Download or read book Automated Machine Learning written by Frank Hutter and published by Springer. This book was released on 2019-05-17 with total page 223 pages. Available in PDF, EPUB and Kindle. Book excerpt: This open access book presents the first comprehensive overview of general methods in Automated Machine Learning (AutoML), collects descriptions of existing systems based on these methods, and discusses the first series of international challenges of AutoML systems. The recent success of commercial ML applications and the rapid growth of the field has created a high demand for off-the-shelf ML methods that can be used easily and without expert knowledge. However, many of the recent machine learning successes crucially rely on human experts, who manually select appropriate ML architectures (deep learning architectures or more traditional ML workflows) and their hyperparameters. To overcome this problem, the field of AutoML targets a progressive automation of machine learning, based on principles from optimization and machine learning itself. This book serves as a point of entry into this quickly-developing field for researchers and advanced students alike, as well as providing a reference for practitioners aiming to use AutoML in their work.

Download or read book An Efficient Computational Model for Premixed Turbulent Combustion at High Reynolds Numbers Based on a Turbulent Flame Speed Closure written by Vladimir Zimont and published by . This book was released on 1997 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Presented at the International Gas Turbine & Aeroengine Congress & Exhibition, Orlando, FL, Jun 2 - Jun 5, 1997.