Download or read book Direct Numerical Simulation of Flame Stabilization Downstream of a Transverse Fuel Jet in Cross flow written by and published by . This book was released on 2010 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effect of Fuel Composition and Differential Diffusion on Flame Stabilization in Reacting Syngas Jets in Turbulent Cross flow written by and published by . This book was released on 2015 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Here, three-dimensional direct numerical simulation results of a transverse syngas fuel jet in turbulent cross-flow of air are analyzed to study the influence of varying volume fractions of CO relative to H2 in the fuel composition on the near field flame stabilization. The mean flame stabilizes at a similar location for CO-lean and CO-rich cases despite the trend suggested by their laminar flame speed, which is higher for the CO-lean condition. To identify local mixtures having favorable mixture conditions for flame stabilization, explosive zones are defined using a chemical explosive mode timescale. The explosive zones related to flame stabilization are located in relatively low velocity regions. The explosive zones are characterized by excess hydrogen transported solely by differential diffusion, in the absence of intense turbulent mixing or scalar dissipation rate. The conditional averages show that differential diffusion is negatively correlated with turbulent mixing. Moreover, the local turbulent Reynolds number is insufficient to estimate the magnitude of the differential diffusion effect. Alternatively, the Karlovitz number provides a better indicator of the importance of differential diffusion. A comparison of the variations of differential diffusion, turbulent mixing, heat release rate and probability of encountering explosive zones demonstrates that differential diffusion predominantly plays an important role for mixture preparation and initiation of chemical reactions, closely followed by intense chemical reactions sustained by sufficient downstream turbulent mixing. The mechanism by which differential diffusion contributes to mixture preparation is investigated using the Takeno Flame Index. The mean Flame Index, based on the combined fuel species, shows that the overall extent of premixing is not intense in the upstream regions. However, the Flame Index computed based on individual contribution of H2 or CO species reveals that hydrogen contributes significantly to premixing, particularly in explosive zones in the upstream leeward region, i.e. at the preferred flame stabilization location. Therefore, a small amount of H2 diffuses much faster than CO, creating relatively homogeneous mixture pockets depending on the competition with turbulent mixing. These pockets, together with high H2 reactivity, contribute to stabilizing the flame at a consistent location regardless of the CO concentration in the fuel for the present range of DNS conditions.

Download or read book Advanced Turbulent Combustion Physics and Applications written by N. Swaminathan and published by Cambridge University Press. This book was released on 2022-01-06 with total page 485 pages. Available in PDF, EPUB and Kindle. Book excerpt: Explore a thorough overview of the current knowledge, developments and outstanding challenges in turbulent combustion and application.

Download or read book Direct Numerical Simulation for Turbulent Reacting Flows written by Thierry Baritaud and published by Editions TECHNIP. This book was released on 1996 with total page 328 pages. Available in PDF, EPUB and Kindle. Book excerpt: Contents: Description of accurate boundary conditions for the simulation of reactive flows. Parallel direct numerical simulation of turbulent reactive flow. Flame-wall interaction and heat flux modelling in turbulent channel flow. A numerical study of laminar flame wall interaction with detailed chemistry: wall temperature effects. Modeling and simulation of turbulent flame kernel evolution. Experimental and theoretical analysis of flame surface density modelling for premixed turbulent combustion. Gradient and counter-gradient transport in turbulent premixed flames. Direct numerical simulation of turbulent flames with complex chemical kinetics. Effects of curvature and unsteadiness in diffusion flames. Implications for turbulent diffusion combustion. Numerical simulations of autoignition in turbulent mixing flows. Stabilization processes of diffusion flames. References.

Download or read book Direct Numerical Simulation of Autoignition in a Jet in a Cross Flow Configuration written by and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Computational Science ICCS 2019 written by João M. F. Rodrigues and published by Springer. This book was released on 2019-06-07 with total page 659 pages. Available in PDF, EPUB and Kindle. Book excerpt: The five-volume set LNCS 11536, 11537, 11538, 11539, and 11540 constitutes the proceedings of the 19th International Conference on Computational Science, ICCS 2019, held in Faro, Portugal, in June 2019. The total of 65 full papers and 168 workshop papers presented in this book set were carefully reviewed and selected from 573 submissions (228 submissions to the main track and 345 submissions to the workshops). The papers were organized in topical sections named: Part I: ICCS Main Track Part II: ICCS Main Track; Track of Advances in High-Performance Computational Earth Sciences: Applications and Frameworks; Track of Agent-Based Simulations, Adaptive Algorithms and Solvers; Track of Applications of Matrix Methods in Artificial Intelligence and Machine Learning; Track of Architecture, Languages, Compilation and Hardware Support for Emerging and Heterogeneous Systems Part III: Track of Biomedical and Bioinformatics Challenges for Computer Science; Track of Classifier Learning from Difficult Data; Track of Computational Finance and Business Intelligence; Track of Computational Optimization, Modelling and Simulation; Track of Computational Science in IoT and Smart Systems Part IV: Track of Data-Driven Computational Sciences; Track of Machine Learning and Data Assimilation for Dynamical Systems; Track of Marine Computing in the Interconnected World for the Benefit of the Society; Track of Multiscale Modelling and Simulation; Track of Simulations of Flow and Transport: Modeling, Algorithms and Computation Part V: Track of Smart Systems: Computer Vision, Sensor Networks and Machine Learning; Track of Solving Problems with Uncertainties; Track of Teaching Computational Science; Poster Track ICCS 2019 Chapter “Comparing Domain-decomposition Methods for the Parallelization of Distributed Land Surface Models” is available open access under a Creative Commons Attribution 4.0 International License via link.springer.com.

Download or read book Direct Numerical Simulation of Bluff body Stabilized Flames written by Farzin Jalilalghadr and published by . This book was released on 2007 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt: Direct numerical simulation (DNS) is used to study reacting and non-reacting bluff-body stabilized flows. Three fuel-to-air velocity ratios were considered. The results show that three types of flow fields can be identified. For the fuel-to-air velocity ratio of 0:84, the flow field is dominated by the reverse flow of the coflowing air. The jet does not penetrate through the reverse flow, and two stagnation points are formed on the centerline, where the jet and air stagnate. The downstream flow field is similar to a wake flow, and therefore this flow is referred to as a bluff-body dominant flow. For the fuel-to-air velocity ratio of 1:4, the flow field is neither dominated by the jet nor the coflowing air and is referred to as an intermittent flow. For the fuel-to-air velocity ratio of 2:8, the jet penetrates through the reverse flow and no stagnation point is formed. The flow field is similar to that of a pure jet, therefore this flow is referred to as a jet dominant flow. In all cases, the coflowing air converges towards the centerline and forms a recirculation zone that extends to approximately one bluff-body diameter downstream. For the reacting flow, the methane combustion is modeled via a global, 1-step kinetic mechanism. The main effects of combustion on the flow field are an increase in the length of the recirculation zone, and a decrease in the velocity fluctuations. Based on the three velocity ratios, three types of flames are produced. For the velocity ratio of 0:84, a short mushroom shaped flame is produced near the fuel stagnation point. For the velocity ratio of 1:4, a medium length flame is produced in the shear layer region between the fuel and air. The flame is anchored in the recirculation zone, and extends downstream of the bluff-body. For the velocity ratio of 2:8, a long flame is produced near the centerline and is also anchored in the recirculation zone. All three flames are stabilized between the coflowing air and the jet, where the strain-rates are low, and the mixture fraction is near the stoichiometric value for methane combustion.

Download or read book Non premixed Combustion Full Numerical Simulation of a Coflowing Axisymmetric Jet Inviscid and Viscous Stability Analysis written by Stanford University. Thermosciences Division. Thermosciences Division and published by . This book was released on 1989 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Direct Numerical Simulation of an Unpremixed Jet Flame written by P. Givi and published by . This book was released on 1986 with total page 65 pages. Available in PDF, EPUB and Kindle. Book excerpt: Direct numerical simulations have been used to study the effects of large coherent structures in two-dimensional, unpremixed, chemically reacting mixing layers under both temporally evolving and spatially developing assumptions. In the temporally evolving mixing layer calculations, a temperature dependent chemical reaction was incorporated into a computer code that uses pseudospectral numerical methods. The nonequilibrium effects leading to the local quenching of a diffusion flame were investigated. Results indicate that the primary important parameter to be considered for flame extinction is the local instantaneous scalar dissipation rate conditioned at the scalar stoichiometric value. At locations where this value is increased beyond a critical value, the local temperature decreases and the instantaneous reaction rate drops to zero, leading to local quenching of the flame. Purposes of simulating spatially developing flows, a two-dimensional, hybrid pseudospectral-finite difference code was constructed. The resulting code was tested with simulations of the pretransitional region of laboratory mixing layers. Examination of some of the statistical quantities obtained from the results of these simulations are in qualitative agreement with recent experimental data obtained at the California Institute of Technology and Stanford University. The asymmetric nature of the mixing processes has been numerically simulated.

Download or read book Mechanisms of Flame Stabilisation at Low Lifted Height in a Turbulent Lifted Slot jet Flame written by and published by . This book was released on 2015 with total page 57 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Reacting Jet Direct Numerical Simulation for Assessing Combustion Model Error written by Bryan William Reuter and published by . This book was released on 2021 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt: The simulation of turbulent combustion systems is a vital tool in the design and development of new technologies for power generation, transportation, defense applications, and industrial heating. In an engineering design cycle, modeling realistic device configurations in a cost- and time-effective manner is required. Due to their flexibility and computational tractability, Reynolds-Averaged Navier-Stokes (RANS)-based models are most commonly used for these purposes. However, these models are known to be inadequate. Turbulent combustion is the coupling of two multiscale, nonlinear phenomena which individually have many modeling challenges. Hence, it is unsurprising that the modeling ansatzes and simplifying assumptions which lead to these practical RANS-based models are suspect. Since RANS-based models will continue to be the dominant tool for turbulent combustion simulation, it is necessary to improve their predictivity through a better understanding of their deficiencies. The are three main modeling issues for turbulent combustion: modeling the turbulent flow, representing the chemical reactions, and capturing the interaction between the turbulence and the chemistry. Model errors can easily be conflated when attempting to quantify deficiencies in this multiphysics context where many individual models are coupled. This work introduces a new technique for isolating these errors through the creation of a flamelet-based direct numerical simulation (DNS) of a nonpremixed, temporally-evolving, planar, reacting jet. DNS is a technique which resolves all lengthscales and timescales of the turbulent flow, providing high-quality data for model development but at a significant computational cost. In the turbulent combustion context, the turbulence-chemistry interaction is also fully resolved. By closing the DNS with a steady laminar flamelet representation, a typical chemical reactions model for RANS-based simulations, RANS turbulence closures and turbulence-chemistry interaction models can be evaluated in isolation through a priori testing. Conversely, by comparing the flamelet DNS to a second DNS employing a higher-fidelity chemistry model, the flamelet closure and its impact on the flame's evolution can be interrogated directly. To obtain the DNS data, a novel algorithm for solving the variable-density, low-Mach Navier-Stokes equations extending the method of Kim, Moin, and Moser for incompressible flow is detailed here. It is a pseudospectral Fourier/B-spline collocation approach which obtains second order accuracy in time and numerical stability for large density ratios with an efficient, matrix-free, iterative treatment of the scalar equations. The a posteriori comparisons of the flamelet DNS and the complex chemistry DNS suggest the flamelet model can significantly alter the evolution of the mean state of the reacting jet; however, violations of global conservation were identified in the complex chemistry DNS. Therefore, no strong conclusions can be made about the chemical reactions model from the comparisons. Significant shortcomings have been identified in the a priori evaluations of the aforementioned RANS closures for turbulent transport, scalar mixing, and turbulence-chemistry interaction, where the flamelet model is taken to be exact. Finally, a flawed assumption in the steady laminar flamelet approach has been directly linked to nonphysical behavior of the density for small values of the scalar dissipation rate

Download or read book Stabilization and Dynamic of Premixed Swirling Flames written by Paul Palies and published by Academic Press. This book was released on 2020-07-03 with total page 402 pages. Available in PDF, EPUB and Kindle. Book excerpt: Stabilization and Dynamic of Premixed Swirling Flames: Prevaporized, Stratified, Partially, and Fully Premixed Regimes focuses on swirling flames in various premixed modes (stratified, partially, fully, prevaporized) for the combustor, and development and design of current and future swirl-stabilized combustion systems. This includes predicting capabilities, modeling of turbulent combustion, liquid fuel modeling, and a complete overview of stabilization of these flames in aeroengines. The book also discusses the effects of the operating envelope on upstream fresh gases and the subsequent impact of flame speed, combustion, and mixing, the theoretical framework for flame stabilization, and fully lean premixed injector design. Specific attention is paid to ground gas turbine applications, and a comprehensive review of stabilization mechanisms for premixed, partially-premixed, and stratified premixed flames. The last chapter covers the design of a fully premixed injector for future jet engine applications. Features a complete view of the challenges at the intersection of swirling flame combustors, their requirements, and the physics of fluids at work Addresses the challenges of turbulent combustion modeling with numerical simulations Includes the presentation of the very latest numerical results and analyses of flashback, lean blowout, and combustion instabilities Covers the design of a fully premixed injector for future jet engine applications

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 Turbulence Coherent Structures Dynamical Systems and Symmetry written by Philip Holmes and published by Cambridge University Press. This book was released on 2012-02-23 with total page 403 pages. Available in PDF, EPUB and Kindle. Book excerpt: Describes methods revealing the structures and dynamics of turbulence for engineering, physical science and mathematics researchers working in fluid dynamics.

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:

Download or read book Unsteady Combustor Physics written by Tim C. Lieuwen and published by Cambridge University Press. This book was released on 2012-08-27 with total page 427 pages. Available in PDF, EPUB and Kindle. Book excerpt: Developing clean, sustainable energy systems is a pre-eminent issue of our time. Most projections indicate that combustion-based energy conversion systems will continue to be the predominant approach for the majority of our energy usage. Unsteady combustor issues present the key challenge associated with the development of clean, high-efficiency combustion systems such as those used for power generation, heating or propulsion applications. This comprehensive study is unique, treating the subject in a systematic manner. Although this book focuses on unsteady combusting flows, it places particular emphasis on the system dynamics that occur at the intersection of the combustion, fluid mechanics and acoustic disciplines. Individuals with a background in fluid mechanics and combustion will find this book to be an incomparable study that synthesises these fields into a coherent understanding of the intrinsically unsteady processes in combustors.

Download or read book Numerical Simulations of Coherent Structures in a Jet Flame with a Noncircular Cross Section written by and published by . This book was released on 1989 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: The presence of coherent structures in turbulent shear flows and their importance in enhancing mixing and entrainment of chemical species has been established in recent years through extensive experimental and numerical studies. When non-premixed combustion is considered, the combustion processes could be enhanced by enhancing the fuel-air mixing and entrainment processes associated with these large coherent structures. In recent experimental studies, the entrainment characteristics of jets with different cross sections were studied, and it was determined that an elliptical jet with a certain cross-sectional shape was more efficient in entraining fluid than a circular jet with the same jet area. This increase was attributed to the complex self-induction process and the subsequent three-dimensional deformation of the elliptical vortex ring during its propagation. To understand the complex flow features associated with elliptical jets with and without heat release, a numerical study was undertaken. A new three-dimensional hybrid Navier-Stokes code was developed using spectral techniques and compact schemes to study the spatial evolution of elliptical jets. The simulation code is now ready for carrying out a detailed study of the effect of jet geometry on the mixing and combustion processes. Keywords: Direct numerical simulations; Elliptical jet flow; Compact schemes; Spectral methods; Turbulent flows; Reacting flows; Heat release; Combustion.