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Numerical Simulation Of Turbulent Premixed Flames With Conditional Source Term Estimation
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Book Synopsis Numerical Simulation of Turbulent Premixed Flames with Conditional Source-term Estimation by : Mohammad Mahdi Salehi
Download or read book Numerical Simulation of Turbulent Premixed Flames with Conditional Source-term Estimation written by Mohammad Mahdi Salehi and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Investigation of Conditional Source-term Estimation Approach for Turbulent Partially Premixed Combustion Modelling by : Daniele Dovizio
Download or read book Investigation of Conditional Source-term Estimation Approach for Turbulent Partially Premixed Combustion Modelling written by Daniele Dovizio and published by . This book was released on 2015 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: Conditional Source-term Estimation (CSE) is a closure technique for modelling turbulent combustion phenomena. CSE uses the Conditional Moment Closure (CMC) hypothesis for closing chemical source terms: conditionally averaged chemical source terms are closed by conditional averaged scalars, which are obtained by inverting an integral equation, instead of solving transport equations (as in CMC). Since CSE has been successfully applied to both premixed and non-premixed configurations, it represents an attractive method for dealing with the more general and complex case of partially premixed combustion. The objectives of the present study are to (i) consolidate the premixed formulation of CSE through numerical simulations of a turbulent bluff body premixed flame; (ii) formulate, implement and test the Doubly conditional CSE (DCSE) in the context of partially premixed combustion; (iii) compare the DCSE predictions with well documented turbulent partially premixed flames. The canonical example of partially premixed flames is represented by turbulent lifted flames. A series of lifted turbulent jet flames is investigated in RANS by using DCSE. The DCSE calculations are successful in predicting the lift-off heights at three different conditions and reproducing many aspects of the flame structure in agreement with the experimental observations. The current results show that important aspects of the stabilization mechanism can be reproduced by the DCSE combustion model. The applicability of DCSE is further evaluated by applying this approach to a series of turbulent V-shaped flames for which experimental data is available. Premixed and stratified conditions are investigated. Overall, the agreement between numerical results and experimental findings is good, demonstrating the capability of DCSE to deal with partially premixed combustion. Future work includes implementation of CSE in LES and investigation of different fuels such as propane and biofuels.
Book Synopsis Direct Numerical Simulation for Turbulent Reacting Flows by : Thierry Baritaud
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.
Book Synopsis Turbulent Combustion Modeling by : Tarek Echekki
Download or read book Turbulent Combustion Modeling written by Tarek Echekki and published by Springer Science & Business Media. This book was released on 2010-12-25 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent combustion sits at the interface of two important nonlinear, multiscale phenomena: chemistry and turbulence. Its study is extremely timely in view of the need to develop new combustion technologies in order to address challenges associated with climate change, energy source uncertainty, and air pollution. Despite the fact that modeling of turbulent combustion is a subject that has been researched for a number of years, its complexity implies that key issues are still eluding, and a theoretical description that is accurate enough to make turbulent combustion models rigorous and quantitative for industrial use is still lacking. In this book, prominent experts review most of the available approaches in modeling turbulent combustion, with particular focus on the exploding increase in computational resources that has allowed the simulation of increasingly detailed phenomena. The relevant algorithms are presented, the theoretical methods are explained, and various application examples are given. The book is intended for a relatively broad audience, including seasoned researchers and graduate students in engineering, applied mathematics and computational science, engine designers and computational fluid dynamics (CFD) practitioners, scientists at funding agencies, and anyone wishing to understand the state-of-the-art and the future directions of this scientifically challenging and practically important field.
Book Synopsis Turbulent Premixed Flames by : Nedunchezhian Swaminathan
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.
Book Synopsis Micro-mixing in Turbulent Premixed Flames by : Michael Joseph Kuron
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.
Book Synopsis Conditional Source-term Estimation Methods for Turbulent Reacting Flows by :
Download or read book Conditional Source-term Estimation Methods for Turbulent Reacting Flows written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Conditional Source-term Estimation (CSE) methods are used to obtain chemical closure in turbulent combustion simulation. A Laminar Flamelet Decomposition (LFD) and then a Trajectory Generated Low-Dimensional Manifold (TGLDM) method are combined with CSE in Reynolds-Averaged Navier Stokes (RANS) simulation of non-premixed autoigniting jets. Despite the scatter observed in the experimental data, the predictions of ignition delay from both methods agree reasonably well with the measurements. The discrepancy between predictions of these two methods can be attributed to different ways of generating libraries that contain information of detailed chemical mechanism. The CSE-TGLDM method is recommended for its seemingly better performance and its ability to transition from autoignition to combustion. The effects of fuel composition and injection parameters on ignition delay are studied using the CSE-TGLDM method. The CSE-TGLDM method is then applied in Large Eddy Simulation of a non-premixed, piloted jet flame, Sandia Flame D. The adiabatic CSE-TGLDM method is extended to include radiation by introducing a variable enthalpy defect to parameterize TGLDM manifolds. The results are compared to the adiabatic computation and the experimental data. The prediction of NO formation is improved, though the predictions of temperature and major products show no significant difference from the adiabatic computation due to the weak radiation of the flame. The scalar fields are then extracted and used to predict the mean spectral radiation intensities of the flame. Finally, the application of CSE in turbulent premixed combustion is explored. A product-based progress variable is chosen for conditioning. Presumed Probability Density Function (PDF) models for the progress variable are studied. A modified version of a laminar flame-based PDF model is proposed, which best captures the distribution of the conditional variable among all PDFs under study. A priori tests are performed with the CSE.
Book Synopsis Subfilter Scale Combustion Modelling for Large Eddy Simulation of Turbulent Premixed Flames by : Nasim Shahbazian
Download or read book Subfilter Scale Combustion Modelling for Large Eddy Simulation of Turbulent Premixed Flames written by Nasim Shahbazian and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Investigation of Conditional Source-term Estimation Approach to Modelling Mild Combustion by : Jeffrey Labahn
Download or read book Investigation of Conditional Source-term Estimation Approach to Modelling Mild Combustion written by Jeffrey Labahn and published by . This book was released on 2016 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt: Conditional Source-term Estimation (CSE) is a turbulent combustion model which uses conditional averages to provide closure for the mean chemical source term and is based on the same ideas as the Conditional Moment Closure (CMC) approach. CSE applies first order closure for the conditional averages which are obtained by inverting an integral equation and has been used to simulate a range of premixed, non-premixed and partially premixed flames. In the present study, CSE is applied to investigate a high efficient, low emission combustion process called Moderate and Intense Low Oxygen Dilution (MILD) combustion. This work represents the first application of CSE for MILD combustion, the first application of a multi-stream CSE formulation and the first doubly-conditioned CSE formulation applied in the Large Eddy Simulation (LES) framework. The objectives of the present study are to i) investigate the CSE combustion model for turbulent non-premixed combustion, ii) develop a CSE formulation for MILD combustion problems, iii) implement CSE for MILD combustion problems in Reynolds-Averaged Navier-Stokes (RANS) and LES and iv) compare the CSE predictions to experimental and previous numerical results for well documented MILD combustion flames. Numerical simulations of a confined non-premixed methane flame are completed using the CSE non-premixed approach. This study investigates the sensitivity to various CSE model parameters and shows CSE is able to accurately predict non-premixed methane combustion. A detailed study of the inversion problem encountered in CSE is also investigated using the Bayesian framework. The origin of the perturbation seen in the unconditional mass fraction in CSE and the impact of a smoothing prior on the recovered solution and credible intervals are discussed. Different regularization methods are studied and it is shown that both zeroth and first order Tikhonov are promising regularization methods for CSE. In the present work, the non-premixed CSE formulation is extended to include the impact of radiation of the conditional reaction rates and is applied to a semi-industrial furnace. This study demonstrates that a RANS-CSE simulation is able to accurately predict the temperature and species concentration, including NOx, for large scale realistic furnace configurations. Finally, a multi-stream CSE formulation is developed and applied to the DJHC burners in the RANS and LES framework. This new CSE formulation is able to predict the temperature and velocity profiles in very good agreement with the experimental data. Further, the LES multi-stream CSE formulation is able to predict the time-dependent nature of the DHJC burners.
Book Synopsis Turbulent Combustion by : Norbert Peters
Download or read book Turbulent Combustion written by Norbert Peters and published by Cambridge University Press. This book was released on 2000-08-15 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt: The combustion of fossil fuels remains a key technology for the foreseeable future. It is therefore important that we understand the mechanisms of combustion and, in particular, the role of turbulence within this process. Combustion always takes place within a turbulent flow field for two reasons: turbulence increases the mixing process and enhances combustion, but at the same time combustion releases heat which generates flow instability through buoyancy, thus enhancing the transition to turbulence. The four chapters of this book present a thorough introduction to the field of turbulent combustion. After an overview of modeling approaches, the three remaining chapters consider the three distinct cases of premixed, non-premixed, and partially premixed combustion, respectively. This book will be of value to researchers and students of engineering and applied mathematics by demonstrating the current theories of turbulent combustion within a unified presentation of the field.
Book Synopsis Large Eddy Simulation of Partially Premixed Flames Using Doubly Conditional Source-term Estimation by : Mohammad Mortada
Download or read book Large Eddy Simulation of Partially Premixed Flames Using Doubly Conditional Source-term Estimation written by Mohammad Mortada and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Direct Numerical Simulations of Premixed Turbulent Flame with Variable Density by : Songwei Zhang
Download or read book Direct Numerical Simulations of Premixed Turbulent Flame with Variable Density written by Songwei Zhang and published by . This book was released on 1994 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis MILD Combustion: Modelling Challenges, Experimental Configurations and Diagnostic Tools by : Alessandro Parente
Download or read book MILD Combustion: Modelling Challenges, Experimental Configurations and Diagnostic Tools written by Alessandro Parente and published by Frontiers Media SA. This book was released on 2021-11-26 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Fundamentals of Premixed Turbulent Combustion by : Andrei Lipatnikov
Download or read book Fundamentals of Premixed Turbulent Combustion written by Andrei Lipatnikov and published by CRC Press. This book was released on 2012-10-24 with total page 548 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
Book Synopsis Application of Conditional Source-term Estimation to Two Turbulent Non-premixed Methanol Flames by :
Download or read book Application of Conditional Source-term Estimation to Two Turbulent Non-premixed Methanol Flames written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Direct Numerical Simulations of Strained Laminar and Turbulent Nonpremixed Flames by : Chunsang Yoo
Download or read book Direct Numerical Simulations of Strained Laminar and Turbulent Nonpremixed Flames written by Chunsang Yoo and published by . This book was released on 2005 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Emission Modeling in Turbulent Premixed Flames by : Hongtao Yang
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.
