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Journal articles on the topic "Flamelettes"
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FURUKAWA, JUNICHI, YOSHIKI NOGUCHI, TOSHISUKE HIRANO, and FORMAN A. WILLIAMS. "Anisotropic enhancement of turbulence in large-scale, low-intensity turbulent premixed propane–air flames." Journal of Fluid Mechanics 462 (July 10, 2002): 209–43. http://dx.doi.org/10.1017/s0022112002008650.
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The density change across premixed flames propagating in turbulent flows modifies the turbulence. The nature of that modification depends on the regime of turbulent combustion, the burner design, the orientation of the turbulent flame and the position within the flame. The present study addresses statistically stationary turbulent combustion in the flame-sheet regime, in which the laminar-flame thickness is less than the Kolmogorov scale, for flames stabilized on a vertically oriented cylindrical burner having fully developed upward turbulent pipe flow upstream from the exit. Under these conditions, rapidly moving wrinkled laminar flamelets form the axisymmetric turbulent flame brush that is attached to the burner exit. Predictions have been made of changes in turbulence properties across laminar flamelets in such situations, but very few measurements have been performed to test the predictions. The present work measures individual velocity changes and changes in turbulence across flamelets at different positions in the turbulent flame brush for three different equivalence ratios, for comparison with theory.The measurements employ a three-element electrostatic probe (EP) and a two-component laser-Doppler velocimeter (LDV). The LDV measures axial and radial components of the local gas velocity, while the EP, whose three sensors are located in a vertical plane that passes through the burner axis, containing the plane of the LDV velocity components, measures arrival times of flamelets at three points in that plane. From the arrival times, the projection of flamelet orientation and velocity on the plane are obtained. All of the EP and LDV sensors are located within a fixed volume element of about 1 mm diameter to provide local, time-resolved information. The technique has the EP advantages of rapid response and good sensitivity and the EP disadvantages of intrusiveness and complexity of interpretation, but it is well suited to the type of data sought here.Theory predicts that the component of velocity tangent to the surface of a locally planar flamelet remains constant in passing through the flamelet. The data are consistent with this prediction, within the accuracy of the measurement. The data also indicate that the component of velocity normal to the flamelet, measured with respect to the flamelet, tends to increase in passing through the flamelet, as expected. The flamelets thereby can generate anisotropy in initially isotropic turbulence. They also produce differences in turbulent spectra conditioned on unburnt or burnt gas. Local modifications of turbulence by flamelets thus are demonstrated experimentally. The modifications are quantitatively different at different locations in the turbulent flame brush but qualitatively similar in that the turbulence is enhanced more strongly in the radial direction than in the axial direction at all positions in these flames.
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Ashurst, W. T., and F. A. Williams. "Vortex modification of diffusion flamelets." Symposium (International) on Combustion 23, no. 1 (January 1991): 543–50. http://dx.doi.org/10.1016/s0082-0784(06)80301-2.
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Hiestermann, Marian, Matthias Haeringer, Marcel Dèsor, and Wolfgang Polifke. "Comparison of non-premixed and premixed flamelets for ultra WET aero engine combustion conditions." Journal of the Global Power and Propulsion Society 8 (October 8, 2024): 370–89. http://dx.doi.org/10.33737/jgpps/188264.
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The Water-Enhanced Turbofan (WET) is a future concept for aero engine applications being developed by MTU Aero Engines AG. Steam is injected into the combustion chamber to reduce temperature peaks and emission of pollutants. Depending on the steam content, the combustion process is modified. To analyze the effect of steam on the reaction kinetics and the temperature, detailed chemistry has to be employed. By comparing laminar flame speed and mole fraction distribution across the flame front, an appropriate chemical mechanism for the considered operating conditions including high steam loads was selected. Tabulated chemistry based on flamelets was employed, which enables the use of complex mechanisms in CFD analysis at reasonable computational costs. A comparison of premixed freely propagating flames and non-premixed counterflow diffusion flames to represent the manifolds was investigated. Various definitions of the progress variable are studied for ultra WET combustion considered under aero engine conditions. The manifolds from both model flames are compared from dry to ultra WET conditions with kerosene in an adapted Sandia Flame D large eddy simulation. While the premixed flamelets are generated efficiently, the results obtained with non-premixed flamelets are more reliable for the range of operating conditions investigated.
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Josephson, Alexander J., Troy M. Holland, Sara Brambilla, Michael J. Brown, and Rodman R. Linn. "Predicting Emission Source Terms in a Reduced-Order Fire Spread Model—Part 1: Particulate Emissions." Fire 3, no. 1 (February 25, 2020): 4. http://dx.doi.org/10.3390/fire3010004.
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A simple, easy-to-evaluate, surrogate model was developed for predicting the particle emission source term in wildfire simulations. In creating this model, we conceptualized wildfire as a series of flamelets, and using this concept of flamelets, we developed a one-dimensional model to represent the structure of these flamelets which then could be used to simulate the evolution of a single flamelet. A previously developed soot model was executed within this flamelet simulation which could produce a particle size distribution. Executing this flamelet simulation 1200 times with varying conditions created a data set of emitted particle size distributions to which simple rational equations could be tuned to predict a particle emission factor, mean particle size, and standard deviation of particle sizes. These surrogate models (the rational equation) were implemented into a reduced-order fire spread model, QUIC-Fire. Using QUIC-Fire, an ensemble of simulations were executed for grassland fires, southeast U.S. conifer forests, and western mountain conifer forests. Resulting emission factors from this ensemble were compared against field data for these fire classes with promising results. Also shown is a predicted averaged resulting particle size distribution with the bulk of particles produced to be on the order of 1 μm in size.
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Bray, Ken. "Laminar Flamelets in Turbulent Combustion Modeling." Combustion Science and Technology 188, no. 9 (June 2, 2016): 1372–75. http://dx.doi.org/10.1080/00102202.2016.1195819.
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Gouldin, F. C., K. N. C. Bray, and J. Y. Chen. "Chemical closure model for fractal flamelets." Combustion and Flame 77, no. 3-4 (September 1989): 241–59. http://dx.doi.org/10.1016/0010-2180(89)90132-6.
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Krass, B. J., B. W. Zellmer, I. K. Puri, and S. Singh. "Application of Flamelet Profiles to Flame Structure in Practical Burners." Journal of Energy Resources Technology 121, no. 1 (March 1, 1999): 66–72. http://dx.doi.org/10.1115/1.2795062.
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Partial premixing can be induced by design in combustors, occurs inadvertently during turbulent nonpremixed combustion, or arises through inadequate fuel-air mixing. Therefore, it is of interest to investigate the effect of partial premixing in a burner that mimics conditions that might occur under practice. In this investigation, we report on similitude of partially premixed flames encountered in practical complex and multi-dimensional burners with simpler, less complex flames, such as counterflow flamelets. A burner is designed to simulate the more complex multi-dimensional flows that might be encountered in practice, and includes the effects of staging, swirl, and possible quenching by introduction of secondary air. The measurements indicate that the structure of partially premixed flames in complex, practical devices can be analyzed in a manner similar to that of flamelets, even if substantial heat transfer occurs. In particular, the flame structure can be characterized in terms of a modified mixture fraction that differentiates the lean and rich zones, and identifies the spatial location of the flame.
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Olson, S. L., F. J. Miller, and I. S. Wichman. "Characterizing fingering flamelets using the logistic model." Combustion Theory and Modelling 10, no. 2 (April 2006): 323–47. http://dx.doi.org/10.1080/13647830600565446.
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Law, C. K., and C. J. Sung. "Structure, aerodynamics, and geometry of premixed flamelets." Progress in Energy and Combustion Science 26, no. 4-6 (August 2000): 459–505. http://dx.doi.org/10.1016/s0360-1285(00)00018-6.
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BYCHKOV, VITALIY, MICHAEL A. LIBERMAN, and RAYMOND REINMANN. "VELOCITY OF TURBULENT FLAMELETS OF FINITE THICKNESS." Combustion Science and Technology 168, no. 1 (July 2001): 113–29. http://dx.doi.org/10.1080/00102200108907833.
Full textDissertations / Theses on the topic "Flamelettes"
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Chikkabikkodu, Krishna Murthy Uday. "Modelling of Turbulence-Combustion Interactions for the Simulation of Fires in Confined and Ventilated Enclosures." Electronic Thesis or Diss., Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2024. http://www.theses.fr/2024ESMA0014.
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La simulation numérique des incendies dans les installations nucléaires présente deux difficultés. D’une part, plusieurs combustibles différents (foyers solides ou liquides) peuvent être impliqués en même temps. D’autre part, les effets du confinement et de la ventilation mécanique peuvent induire des effets de pression dans le compartiment, et conduire transitoirement à des puissances de feu plus élevées qu’en milieu ouvert. Dans ce contexte, l’approche EDM(Eddy Dissipation Model), souvent utilisée pour la simulation des flammes non-prémélangées rencontrées en incendie, décrit les taux de réaction uniquement à partir du temps caractéristique de la turbulence, et néglige les interactions de la turbulence avec la chimie et les transferts thermiques. Cette approche surestime la température de la flamme, et ne permet ni la prédiction des concentrations d’espèces chimiques intermédiaires(monoxyde de carbone, imbrûlés, suies), ni la description des extinctions et ré-inflammations locales induites par l’étirement ou des pertes radiatives. La présente étude se concentre donc sur le développement d’un modèle de combustion turbulente basé sur l’approche Steady Laminar Flamelet Model (SLFM), qui suppose que le temps caractéristique des réactions chimiques est petit, mais fini, comparé au temps caractéristique turbulent. Dans un premier temps, l’approche SLFM est appliquée à la simulation RANS de la flamme jet Sandia D. Elle permet de mieux représenter le champ de température et la structure chimique de la flamme que l’approche EDM. L’approche SLFMest ensuite généralisée pour tenir compte des entrées multiples de combustible et de comburant, par l’introduction de scalaires passifs supplémentaires, appelés traceurs d’entrée. Ce modèle multi-entrées est validé par les simulations RANS et LES du brûleur JHC d’Adélaïde, qui comporte deux entrées distinctes d’oxydant. La modélisation multi-entrées permet bien de reproduire les champs de température et de concentration, et de prendre en compte les effets de dilution. L’approche SLFM est enfin testée sur deux cas d’application incendie. Le premier, un panache de méthanol en milieu ouvert, est simulé avec le modèle de flamelettes à deux entrées. La structure chimique de la flamme, les niveaux de température et les espèces intermédiaires sont bien estimés. Le second cas concerne la phase de puissance maximale d’un feu de boîte à gants. Cette configuration est simulée à l’aide de l’approche SLFM à plusieurs entrées, du fait de la présence de de deux combustibles distincts. Les pertes radiatives sont modélisées de manière simplifiée. Ces deux cas montrent la capacité de l’approche SLFM à prédire la structure chimique des flammes rencontrées en incendieNumerical simulation of fires in nuclear facilities presents two difficulties. Firstly, several different fuels (solid or liquid fires) may be involved at the same time. Secondly, the effects of containment and mechanical ventilation can induce pressure effects in the compartment, leading transiently to higher fire powers than in an open environment. In this context, the EDM (Eddy Dissipation Model) approach, often used to simulate non-premixed flames encountered in fires, describes reaction rates based solely on the characteristic time of turbulence, and neglects the interactions of turbulence with chemistry and heat transfer. This approach overestimates flame temperature, and fails to predict the concentrations of intermediate chemical species (carbon monoxide, unburnt fuel, soot),or to describe local extinctions and reignitions induced by stretching or radiative losses. The present study therefore focuses on the development of a turbulent combustion model based on the Steady Laminar Flamelet Model (SLFM) approach, which assumes that the characteristic time of chemical reactions is small, but finite, compared to flow time scales. The model is first applied to the RANS simulation of the Sandia D jet flame. It provides a better representation of the temperature field and chemical structure of the flame than the EDM approach. The SLFM approach is then generalised to accommodate multiple fuel and oxidiser inlets, by introducing additional passive scalars, called inlet tracers. The model is validated by carrying out RANS and LES of the Adelaide JHC burner, which features two distinct oxidiser inlets. Multiple-inlet modelling enables temperature and concentration fields to be well reproduced, and dilution effects to be taken into account. Finally, the SLFM approach is tested on two fire applications. The first, an open methanol pool fire is simulated with the two-inlet flamelet model. The chemical structure of the flame, temperature levels and the intermediate species are well estimated. The second case concerns the maximum power phase of a glovebox fire. This configuration is simulated using the multi-inlet SLFM approach, due to the presence of two distinct fuels. Radiative losses are modelled in a simplified way. These two cases demonstrate the ability of the SLFM approach to predict the chemical structure of flames encountered in fires
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Langella, Ivan. "Large eddy simulation of premixed combustion using flamelets." Thesis, University of Cambridge, 2016. https://www.repository.cam.ac.uk/handle/1810/254303.
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Large Eddy Simulation (LES) has potential to address unsteady phenomena in turbulent premixed flames and to capture turbulence scales and their influence on combustion. Thus, this approach is gaining interest in industry to analyse turbulent reacting flows. In LES, the dynamics of large-scale turbulent eddies down to a cut-off scale are solved, with models to mimic the influences of sub-grid scales. Since the flame front is thinner than the smallest scale resolved in a typical LES, the premixed combustion is a sub-grid scale (SGS) phenomenon and involves strong interplay among small-scale turbulence, chemical reactions and molecular diffusion. Sub-grid scale combustion models must accurately represent these processes. When the flame front is thinner than the smallest turbulent scale, the flame is corrugated by the turbulence and can be seen as an ensemble of thin, one-dimensional laminar flames (flamelets). This allows one to decouple turbulence from chemistry, with a significant reduction in computational effort. However, potentials and limitations of flamelets are not fully explored and understood. This work contributes to this understanding. Two models are identified, one based on an algebraic expression for the reaction rate of a progress variable and the assumption of fast chemistry, the other based on a database of unstrained flamelets in which reaction rates are stored and parametrised using a progress variable and its SGS variance, and their potentials are shown for a wide range of premixed combustion conditions of practical interest. The sensitivity to a number of model parameters and boundary conditions is explored to assess the robustness of these models. This work shows that the SGS variance of progress variable plays a crucial role in the SGS reaction rate modelling and cannot be obtained using a simple algebraic closure like that commonly used for a passive scalar. The use of strained flamelets to include the flame stretching effects is not required when the variance is obtained from its transport equation and the resolved turbulence contains predominant part of the turbulent kinetic energy. Thus, it seems that SGS closure using unstrained flamelets model is robust and adequate for wide range of turbulent premixed combustion conditions.
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Hyde, S. M. "Field modeling of carbon monoxide production in vitiated compartment fires." Thesis, Cranfield University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341050.
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Zheng, Li Li. "Studies of hydrogen-air turbulent diffusion flames for subsonic and supersonic flows." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319464.
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Deon, Diego Luis. "Estudo numérico de chamas turbulentas não pré-misturadas através de modelos baseados no conceito de flamelets." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/141148.
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A simulação numérica de chamas turbulentas é ainda hoje um desafio para as práticas de mecânica dos fluidos computacional. Compreendendo que as abordagens numéricas mais completas e realísticas atualmente disponíveis podem ser computacionalmente proibitivas, diversos modelos vêm sendo desenvolvidos com o objetivo de reproduzir os fenômenos envolvidos na combustão de uma forma simplificada, mas ainda fisicamente consistente. Este trabalho é, portanto, dedicado à comparação de diferentes modelos de fechamento para a turbulência baseados nas equações de Navier-Stokes em médias de Reynolds e de modelos para simplificação da cinética química baseados no conceito de flamelets, com e sem a modelagem da radiação térmica, esta última através do modelo de soma-ponderada-de-gasescinzas. Para tanto, na primeira parte do presente trabalho são comparados seis modelos de turbulência na solução de um jato turbulento de propano, não reativo e isotérmico, circundado por uma corrente paralela de ar, quanto a sua eficiência na predição dos valores médios da velocidade longitudinal e transversal, fração mássica de propano e massa específica da mistura. Os modelos são o k- Padrão (empregado na sua versão original e com mais duas modificações nas suas constantes conforme propostas encontradas na literatura), o k- Realizable, o k- Padrão e o k- Shear-Stress Transport. Um dos modelos de melhor desempenho é então usado na simulação de uma chama turbulenta não pré-misturada de metano/hidrogênio/nitrogênio circundada por um escoamento coaxial de ar de baixa velocidade, no qual são então comparados os modelos para redução da cinética química baseados no conceito de flamelets, o Steady Laminar Diffusion Flamelet (SLDF) e o Flamelet-Generated Manifold (FGM), tendo os seus resultados comparados aos dados experimentais para os valores médios da velocidade longitudinal, fração de mistura, temperatura e frações mássicas das espécies químicas. Dentre os modelos de turbulência avaliados, é observado que as duas versões ajustadas do k- Padrão e o k- Padrão se mostraram com melhor concordância em relação às medições experimentais do que os demais. No presente estudo é também avaliada a consistência dos dados experimentais reportados e uma discrepância é identificada neste jato, mas que, conforme verificado, não compromete a comparação dos modelos aqui proposta. Na solução do escoamento reativo, o modelo SLDF se mostrou com resultados bastante próximos aos resultados experimentais (exceto para o NO), sendo aprimorados ainda mais com a inclusão da modelagem da radiação térmica, sobretudo para regiões mais distantes do bico injetor do combustível, após o pico de temperatura da chama. O modelo FGM, contudo, apresentou resultados muito aquém dos esperados, sobretudo para as frações mássicas das espécies químicas, mesmo utilizando malhas com nível de refinamento muito maior e com o teste de diversas combinações de espécies para a variável de progresso da reação, e no qual a inclusão da radiação na modelagem também não trouxe benefícios perceptíveis. Todas as simulações numéricas foram realizadas empregando o código comercial ANSYS Fluent, versão 15.0.0.The numerical simulation of turbulent flames is still a challenge for today's computational fluid dynamics practices. Understanding that the most complete and realistic numerical approaches available today may be computationally prohibitive, several models have been developed in order to reproduce the phenomena involved in combustion in a simplified, but still physically consistent, way. Therefore, this work is dedicated to compare different models for turbulence closure based on the Reynolds-averaged Navier-Stokes equations and models for simplification of the chemical kinetics based on the flamelet concept, with and without thermal radiation modeling through the weighted-sum-of-gray-gases model. Thus, in the first part of the current work six turbulence models are employed to solve a turbulent nonreactive isothermal flow, a propane jet surrounded by a parallel stream of air. The models are compared through their effectiveness in predicting the mean values of longitudinal and transversal velocities, propane mass fraction and mixture density. The models are the Standard k- (employed in its original version and with two modifications according to proposals found in the literature), the Realizable k- , the Standard k- and the Shear-Stress Transport k- . One of the best performing models is then used to simulate a turbulent nonpremixed flame of methane/hydrogen/nitrogen surrounded by a low-velocity air coflow, in which are compared the models to reduce the chemical kinetics based on the flamelets concept, the Steady Laminar Diffusion Flamelet (SLDF) and the Flamelet-Generated Manifold (FGM), being the numerical results compared to the experimental data for the mean values of longitudinal velocity, mixture fraction, temperature and species mass fractions. Among the six turbulence models evaluated, it is observed that the two adjusted versions of the Standard k- and the Standard k- showed better agreement with the experimental measurements than the other models. In the current study it is also evaluated the consistency of the reported experimental data and a discrepancy is identified, which, as verified, does not compromise the models comparison here proposed. In the solution of the reactive flow, the SLDF model showed results very close to the experimental results (except for NO), being further enhanced with the inclusion of the thermal radiation modeling, especially for regions far from fuel nozzle, after the peak of temperature of the flame. The FGM model, however, showed results far below the expected, especially for the mass fractions of chemical species, even using meshes with much higher refinement level and testing of various species combinations for the reaction progress variable. The inclusion of the radiation modeling did not brought noticeable benefits. All the numerical simulations were performed employing the ANSYS Fluent version 15.0.0 commercial code.
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Vallinayagam, pillai Subramanian. "Modélisation de la combustion turbulente : application des méthodes de tabulation de la chimie détaillée l'allumage forcé." Thesis, Rouen, INSA, 2010. http://www.theses.fr/2010ISAM0001/document.
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L'optimisation des systèmes d'allumage est un paramètre critique pour la définition des foyers de combustion industriels. Des simulations aux grandes échelles (ou LES pour Large-Eddy Simulation) d'un brûleur de type bluff-body non pré-mélangé ont été menées afin de comprendre l'influence de la position de la bougie sur la probabilité d'allumage. La prise en compte de la combustion est basée sur une méthode de tabulation de la chimie détaillée (PCM-FPI pour Presumed Conditional Moments - Flame Prolongation of ILDM). Les résultats de ces simulations ont été confrontés des résultats expérimentaux disponibles dans la littérature. Dans un premier temps, les mesures de vitesse et du champ de richesse à froid sont comparées aux résultats de la simulation pour évaluer les capacités de prédiction en terme de structure de l'écoulement et de mélange turbulent. Un suivi temporel des vitesses et de la fraction de mélange est réalisé à différents points pour déterminer les fonctions de densité de probabilité (ou PDF)des variables caractéristiques de l'écoulement, à partir des champs résolus en LES. Les PDFs ainsi obtenues servent l'analyse des phénomènes d'allumages réussis ou déficients rencontrés expérimentalement. Des simulations d'allumage forcé ont été effectuées pour analyser les différents scénarios de développement de la flamme. Les corrélations entre les valeurs locales (fraction de mélange, vitesse) autour de la position d'allumage et les chances de succès de développement du noyau de gaz brûlés sont alors discutées. Enfin, une extension de la méthode PCM-FPI avec prise en compte des effets d'étirement est développée à l'aide d'une analyse asymptotique, puis confrontée aux résultats de mesures expérimentalesThe optimization of the ignition process is a crucial issue in the design of many combustion systems. Large eddy simulation (LES) of a conical shaped bluff-body turbulent non-premixed burner has been performed to study the impact of spark location on ignition success. The chemistry part of the simulation is done using tabulated detailed chemistry approach. This burner was experimentally investigated by Ahmed et al at Cambridge (UK). The present work focuses on the case without swirl for which detailed measurements are available. First, cold fkow measurements of velocities and mixture fraction are compared with their LES counterparts, to assess the prediction capabilities of simulations in terms of flow and turbulent mixing. Time history of velocities and mixture fraction are recorded at selected spots, to probe the resolved probability density function (pdf) of flow variables, in an attempt to reproduce, from the knowledge of LES resolved instantaneous flow conditions, the experimentally observed reasons of success or failure of spark ignition. A flammability map is also constructed from the resolved mixture fraction pdf and compared with its experimental counterpart. LES of forced ignition is then performed using flamelet fully detailed tabulated chemistry combined with presumed pdfs (PCM-FPI). Various scenarios of flame kernel development are analyzed and correlated with typical flow conditions observed in this burner. The correlations between velocities and mixture fraction values at the sparking time and the success or failure of ignition are then further discussed and analysed. The rate of flame development during successful or unsuccessful ignition events are analysed and compared against experimental observations. Finally, from asymptotic flame analysis, a novel approach has been proposed to include flame straining effects in the PCM-FPI method developped at CORIA-CNRS. The new model overcomes the problem associated with classical PCM-FPI closure to model kernel quenching due to intense local turbulence. Computations are done including the flame straining effects and the effect brought by the new model on kernel development is analysed in detail
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Claramunt, Altimira Kilian. "Numerical Simulation of Non-premixed Laminar and Turbulent Flames by means of Flamelet Modelling Approaches." Doctoral thesis, Universitat Politècnica de Catalunya, 2005. http://hdl.handle.net/10803/6680.
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Deep knowledge of combustion phenomena is of great scientific and technological interest. In fact, better design of combustion equipments (furnaces, boilers, engines, etc) can contribute both in the energy efficiency and in the reduction of pollutant formation. One of the limitations to design combustion equipments, or even predict simple flames, is the resolution of the mathematical formulation. Analytical solutions are not feasible, and recently numerical techniques have received enormous interest. Even though the ever-increasing computational capacity, the numerical resolution requires large computational resources due to the inherent complexity of the phenomenon (viz. multidimensional flames, finite rate kinetics, radiation in participating media, turbulence, etc). Thus, development of capable mathematical models reducing the complexity and the stiffness as well as efficient numerical techniques are of great interest.
The main contribution of the thesis is the analysis and application of the laminar flamelet concept to the numerical simulation of both laminar and turbulent non-premixed flames. Assuming a one-dimensional behavior of combustion phenomena in the normal direction to the flame front, and considering an appropriate coordinates transformation, flamelet approaches reduce the complexity of the problem.
The numerical methodology employed is based on the finite volume technique and a parallel multiblock algorithm is used obtaining an excellent parallel efficiency. A post-processing verification tool is applied to assess the quality of the numerical solutions.
Before dealing with flamelet approaches, a co-flow partially premixed methane/air laminar flame is studied for different levels of partial premixing. A comprehensive study is performed considering different mathematical formulations based on the full resolution of the governing equations and their validation against experimental data from the literature. Special attention is paid to the prediction of pollutant formation.
After the full resolution of the governing equations, the mathematical formulation of the flamelet equations and a deep study of the hypothesis assumed are presented. The non-premixed methane/air laminar flame is considered to apply the flamelet modelling approach, comparing the results with the simulations obtained with the full resolution of the governing equations. Steady flamelets show a proper performance to predict the main flame features when differential diffusion and radiation are neglected, while unsteady flamelets are more suitable to account for these effects as well as pollutant formation. Assumptions of the flamelet equations, the scalar dissipation rate modelling, and the evaluation of the Lagrangian flamelet time for unsteady flamelets are specially analysed.
For the numerical simulation of turbulent flames, the mathematical formulation based on mass-weighted time-averaging techniques, using RANS EVM two-equation models is considered. The laminar flamelet concept with a presumed PDF is taken into account. An extended Eddy Dissipation Concept model is also applied for comparison purposes. A piloted non-premixed methane/air turbulent flame is studied comparing the numerical results with experimental data from the literature. A clear improvement in the prediction of slow processes is shown when the transient term in the flamelet equations is retained. Radiation is a key aspect to properly define the thermal field and, consequently, species such as nitrogen oxides. Finally, the consideration of the round-jet anomaly is of significant importance to estimate the flame front position.
In conclusion, flamelet modelling simulations are revealed to be an accurate approach for the numerical simulation of laminar and turbulent non-premixed flames. Detailed chemistry can be taken into account and the stiffness of the chemistry term is solved in a pre-processing task. Pollutant formation can be predicted considering unsteady flamelets.
Books on the topic "Flamelettes"
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Pitz, R. W. Comparison of reaction zones in turbulent lifted diffusion flames to stretched laminar flamelets. Washington, D.C: American Institute of Aeronautics and Astronautics, 1992.
Find full textBook chapters on the topic "Flamelettes"
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Gouldin, F. C. "A Fractal Description of Flamelets." In Lecture Notes in Engineering, 278–306. New York, NY: Springer US, 1989. http://dx.doi.org/10.1007/978-1-4613-9631-4_17.
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Dold, J. W. "Ends of Laminar Flamelets: Their Structure, Behaviour and Implications." In Nonlinear PDE’s in Condensed Matter and Reactive Flows, 99–113. Dordrecht: Springer Netherlands, 2002. http://dx.doi.org/10.1007/978-94-010-0307-0_4.
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Yoshida, A. "Time Scale Distribution of Laminar Flamelets in Turbulent Premixed Flames." In Laser Diagnostics and Modeling of Combustion, 281–86. Berlin, Heidelberg: Springer Berlin Heidelberg, 1987. http://dx.doi.org/10.1007/978-3-642-45635-0_36.
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Davidovic, Marco, Mathis Bode, and Heinz Pitsch. "On Parallelization Strategies for Multiple Representative Interactive Flamelets Combustion Models." In High Performance Computing in Science and Engineering '19, 279–93. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-66792-4_19.
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Williams, F. A. "Structure of Flamelets in Turbulent Reacting Flows and Influences of Combustion on Turbulence Fields." In Lecture Notes in Engineering, 195–212. New York, NY: Springer US, 1989. http://dx.doi.org/10.1007/978-1-4613-9631-4_12.
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"Numerical Simulations of Interactions of Flamelets with Shock Waves in the Premixed Gas." In Dynamics of Gaseous Combustion, 274–83. Washington DC: American Institute of Aeronautics and Astronautics, 1993. http://dx.doi.org/10.2514/5.9781600866241.0274.0283.
Full textConference papers on the topic "Flamelettes"
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Neumeier, Yedidia, and Ben Zinn. "Heuristic Modeling of Diffusion Flamelets." In 43rd AIAA Aerospace Sciences Meeting and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2005. http://dx.doi.org/10.2514/6.2005-150.
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Ketelheun, Anja, Clemens Olbricht, Frederik Hahn, and Johannes Janicka. "Premixed Generated Manifolds for the Computation of Technical Combustion Systems." In ASME Turbo Expo 2009: Power for Land, Sea, and Air. ASMEDC, 2009. http://dx.doi.org/10.1115/gt2009-59940.
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Large eddy simulations (LES) show a good prediction accuracy at a decent computational cost for the simulation of combustion processes in complex geometries. However, the large grids required make the direct solution of detailed reaction kinetics impracticable. Therefore, the chemical reactions can be tabulated in a pre-processing step using detailed chemistry with one-dimensional laminar steady flamelets. These flamelets can be either non-premixed or premixed and are stored based on controlling variables like mixture fraction and reaction progress parameter, for example. In this work, a progress variable approach (PVA) using premixed flamelets was adopted to generate a manifold defined by mixture fraction and reaction progress variable. Since the computation of the flamelets is only feasible between flammability limits, the data outside these limits has to be extrapolated to obtain the complete manifold for all chemical states. The extrapolation influences the stability of the LES and its prediction quality and so four different extrapolation schemes were studied. A probability density function (PDF) model was applied to account for subgrid scale variances. Two methods of modeling the joint PDF of mixture fraction and progress variable in terms of their statistical dependence were investigated. Some results of a bluff body configuration comparing the PDF modeling approaches are shown. The results demonstrated that a diffusion flame can be simulated with both the progress variable approach based on premixed flamelets and classic non-premixed flamelets without progress variable.
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Both, Ambrus, Daniel Mira, and Oriol Lehmkuhl. "ASSESSMENT OF TABULATED CHEMISTRY MODELS FOR THE LES OF A MODEL AERO-ENGINE COMBUSTOR." In GPPS Chania22. GPPS, 2022. http://dx.doi.org/10.33737/gpps22-tc-70.
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Tabulated chemistry methods present a compromise between computational cost and the ability to capture complex combustion physics in high-fidelity numerical simulations. The application of such models entails a number of modeling decisions, that may affect the simulation results significantly, especially in partially premixed combustion, where the assumption of the existence of underlying premixed or non-premixed flamelet structures is arguable. In this work, different classical tabulation strategies are assessed in terms of their ability to predict the lift-off induced by localized extinction in a model aero-engine combustion chamber: the Cambridge swirl spray flame. The lift-off dynamics of the stable n-heptane spray flame are compared using: i) premixed flamelets, ii) stable and unstable counterflow diffusion flamelets, iii) stable and unsteady extinguishing counterflow diffusion flamelets, iv) unsteady extinguishing and reigniting counterflow diffusion flamelets at a given strain rate. The extinction and reignition events associated to the lift-off are validated against OH-PLIF measurements, and the temporal evolution of the lift-off and reattachment is analyzed.
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Wang, M., M. Raju, E. Pomraning, P. Kundu, Y. Pei, and S. Som. "Comparison of Representative Interactive Flamelet and Detailed Chemistry Based Combustion Models for Internal Combustion Engines." In ASME 2014 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/icef2014-5522.
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Representative Interactive Flamelet (RIF) and Detailed Chemistry based combustion models are two commonly used combustion models for non-premixed diesel engine simulations. RIF performs transient chemistry calculations on a one-dimensional grid based on the mixture fraction coordinate. Hence, the chemistry calculations are essentially decoupled from the computational fluid dynamics (CFD) grid. The detailed chemistry model, on the other hand, solves transient chemistry in the 3D CFD domain. An efficient parallelization strategy is used for the computation of the multiple flamelets RIF model. The multiple flamelets RIF and detailed chemistry combustion models are applied for modeling a constant volume spray combustion case and a diesel engine case, with a view to compare the differences between the two models. Results for ignition delay, flame lift-off length, cylinder pressure, and emissions are compared with experimental data. The effect of number of flamelets is evaluated. Finally, the effect of spray cooling is investigated based on the results from the RIF model and the detailed chemistry based combustion model.
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Goldin, Graham, Zhuyin Ren, Hendrik Forkel, Liuyan Lu, Venkat Tangirala, and Hasan Karim. "Modeling CO With Flamelet-Generated Manifolds: Part 1—Flamelet Configuration." In ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/gt2012-69528.
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In laminar flamelet modeling, a laminar flame in a simple 0D or 1D configuration is calculated a-priori and parameterized by a few scalars such as mixture fraction and reaction-progress or strain-rate. Transport equations, or algebraic expressions, for these parameters are then solved in 3D CFD simulations, avoiding computationally expensive in-situ chemical kinetic calculations. Typical configurations for laminar flamelets include, in 1D, opposed flow configurations with either non-premixed or premixed streams, freely propagating premixed flames, premixed flames impinging on a (heated) wall, and burner stabilized premixed flames. In 0D, plug-flow, perfectly-stirred (PSR) and partially-stirred reactors have been employed to build ‘flamelet-like’ ignition and flame-propagation tables. This paper compares 1D strained steady and unsteady non-premixed flamelets, 1D strained premixed flamelets, and 0D PSR simulations at a stochiometric and a lean equivalence ratio. At stochiometric mixtures, all three flamelet configurations show comparable manifolds (i.e. CO and OH mass fractions, and reaction-progress source term distributions). However, at lean equivalence ratios, the different configurations show substantially different manifolds. It is concluded that a unique flamelet configuration cannot be identified for a general partially-premixed model that ranges from the non-premixed to the perfectly premixed limit. Instead, to accurately model CO emissions, it may be necessary to include both premixed and non-premixed flamelets, with a flame-index (e.g. Yamashita et al., 1996, Proc. Combust. Inst., 26) to select the appropriate burning regime.
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Hiestermann, Marian, Matthias Haeringer, Marcel Désor, and Wolfgang Polifke. "Comparison of non-premixed and premixed flamelets for ultra wet aero engine combustion conditions." In GPPS Hong Kong24. GPPS, 2023. http://dx.doi.org/10.33737/gpps23-tc-277.
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The Water-Enhanced Turbofan (WET) is a future concept for aero engine applications being developed by MTU Aero Engines AG. Steam is injected into the combustion chamber to reduce temperature peaks and emission of pollutants. Depending on the steam content, the combustion process is modified. To analyze the effect of steam on the reaction kinetics and the temperature, detailed chemistry has to be employed. By comparing laminar flame speed and mole fraction distribution across the flame front, an appropriate chemical mechanism for the considered operating conditions including high steam loads was selected. Tabulated chemistry based on flamelets was employed, which enables the use of complex mechanisms in CFD analysis at reasonable computational costs. A comparison of premixed freely propagating flames and non-premixed counterflow diffusion flames to represent the manifolds was investigated. Various definitions of the progress variable are studied for ultra WET combustion considered under aero engine conditions. The manifolds from both model flames are compared from dry to ultra WET conditions with kerosene in an adapted Sandia Flame D large eddy simulation. While the premixed flamelets are generated efficiently, the results obtained with non-premixed flamelets are more reliable for the range of operating conditions investigated.
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Croce, Giulio, Giulio Mori, Viatcheslav V. Anisimov, and Joa˜o Parente. "Assessment of Traditional and Flamelets Models for Micro Turbine Combustion Chamber Optimisation." In ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/gt2003-38385.
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Different approaches for numerical simulation of premixed combustion are considered, in order to assess their usefulness as design tools for micro gas turbine systems. In particular, a flamelet concept routine by N. Peters has been developed taking into account both mixture fraction Z and G function as scalar flame locators, thus allowing computation of complex fully or partial premixed flame structure. The model can be used also in the thin reaction regime. Scalar transport equations for G, Z and their variance are added to the standard Navier Stokes and turbulence set of equation, in order to track the flame position. However, no chemical term appears explicitly in such equations, since the chemical effects are taken into account via pre-computed locally one-dimensional flamelet solutions. Here, the deep interaction between chemical and turbulence has been introduced through flamelets library built in non equilibrium conditions using CHEMKIN modules. The results of this model are compared the data obtained with a standard EBU model and different reaction mechanisms. Models validation has been carried out through experimental data coming from Aachen University for an axisymmetric Bunsen flame; finally, the code was applied to the analysis of a newly designed micro gas turbine combustor.
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PITZ, R., S. NANDULA, and T. BROWN. "Comparison of reaction zones in turbulent lifted diffusion flames tostretched laminar flamelets." In 28th Joint Propulsion Conference and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1992. http://dx.doi.org/10.2514/6.1992-3349.
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MILLER, RICHARD. "The manifestation of eddy shocklets and laminar diffusion flamelets in a shear layer." In 31st Aerospace Sciences Meeting. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1993. http://dx.doi.org/10.2514/6.1993-11.
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Hasse, C., H. Barths, and N. Peters. "Modelling the Effect of Split Injections in Diesel Engines Using Representative Interactive Flamelets." In International Fuels & Lubricants Meeting & Exposition. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 1999. http://dx.doi.org/10.4271/1999-01-3547.
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