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Author : Robert A. Shankland
Publisher :
ISBN 13 :
Total Pages : 174 pages
Book Rating : 4.:/5 (357 download)
Download or read book Structure of Partially Premixed Turbulent Jet Flames written by Robert A. Shankland and published by . This book was released on 1995 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Tenghai Wang
Publisher :
ISBN 13 :
Total Pages : 152 pages
Book Rating : 4.:/5 (41 download)
Download or read book Flame Structure and Pollutant Emission Characteristics of Turbulent Partially Premixed Flames in a Co-axial Jet Burner written by Tenghai Wang and published by . This book was released on 1998 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : S. K. Sadasivuni
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (757 download)
Download or read book LES Modelling of Non-premixed and Partially Premixed Turbulent Flames written by S. K. Sadasivuni and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A large eddy simulation (LES) model has been developed and validated for turbulent non-premixed and partially premixed combustion systems. LES based combustion modelling strategy has the ability to capture the detailed structure of turbulent flames and account for the effects of radiation heat loss. Effects of radiation heat loss ismodelled by employing an enthalpy-defect based non-adiabatic flamelet model (NAFM) in conjunction with a steady non-adiabatic flamelet approach. The steady laminar flamelet model (SLFM) is used with multiple flamelet solutions through thedevelopment of pre-integrated look up tables. The performance of the non-adiabatic model is assessed against experimental measurements of turbulent CH4/H2 bluff-body stabilized and swirl stabilized jet flames carried out by the University of Sydney combustion group. Significant enhancements in the predictions of mean thermal structure have been observed with both bluff body and swirl stabilized flames by the consideration of radiation heat loss through the non-adiabatic flamelet model. In particular, mass fractions of product species like CO2 and H2O have been improved with the consideration of radiation heat loss. From the Sydney University data the HM3e flame was also investigated withSLFM using multiple flamelet strategy and reasonably fair amount of success has been achieved. In this work, unsteady flamelet/progress variable (UFPV) approach based combustion model which has the potential to describe both non-premixed and partially premixed combustion, has been developed and incorporated in an in-house LES code. The probability density function (PDF) for reaction progress variable and scalardissipation rate is assumed to follow a delta distribution while mixture fraction takes the shape of a beta PDF. The performance of the developed model in predicting the thermal structure of a partially premixed lifted turbulent jet flame in vitiated co-flow has been evaluated. The UFPV model has been found to successfully predict the flame lift-off, in contrast SLFM results in a false attached flame. The mean lift-off height is however over-predicted by UFPV-? function model by ~20% for methane based flame and under-predicted by ~50% for hydrogen based flame. The form of thePDF for the reaction progress variable and inclusion of a scalar dissipation rate thusseems to have a strong influence on the predictions of gross characteristics of the flame. Inclusion of scalar dissipation rate in the calculations appears to be successful in predicting the flame extinction and re-ignition phenomena. The beta PDFdistribution for the reaction progress variable would be a true prospect for extending the current simulation to predict the flame characteristics to a higher degree.
Author : Norbert Peters
Publisher : Cambridge University Press
ISBN 13 : 1139428063
Total Pages : 322 pages
Book Rating : 4.1/5 (394 download)
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.
Author : Nedunchezhian Swaminathan
Publisher : Cambridge University Press
ISBN 13 : 1139498584
Total Pages : 447 pages
Book Rating : 4.1/5 (394 download)
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.
Author : Tarek Echekki
Publisher : Springer Science & Business Media
ISBN 13 : 9400704127
Total Pages : 496 pages
Book Rating : 4.4/5 (7 download)
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.
Author : Andrej S. Mitrovic
Publisher :
ISBN 13 :
Total Pages : 322 pages
Book Rating : 4.:/5 (394 download)
Download or read book Internal Structure and Soot Emission Characteristics of Partially Premixed Coaxial Jet Flames written by Andrej S. Mitrovic and published by . This book was released on 1998 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : S. Ruan
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (847 download)
Download or read book Turbulent Partially Premixed Combustion written by S. Ruan and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Increasingly stringent regulation of pollutant emission has motivated the search for cleaner and more efficient combustion devices, which remain the primary means of power generation and propulsion for all kinds of transport. Fuel-lean premixed combustion technology has been identified to be a promising approach, despite many difficulties involve, notably issues concerning flame stability and ignitability. A partially premixed system has been introduced to remedy these problems, however, our understanding on this combustion mode needs to be greatly improved to realise its full potential. This thesis aims to further the understanding of various fundamental physical processes in turbulent partially premixed flames. DNS data of a laboratory-scale hydrogen turbulent jet lifted flame is analysed in this study. The partially premixed nature of this flame is established by examining the instantaneous and averaged reaction rates and the "Flame Index", which indicate premixed and diffusion burning modes coexisting. The behaviour of turbulent flame stretch and its relation to other physical processes, in particular the scalar-turbulence interaction, the effects of partial premixing on the displacement speed of iso-scalar surface and its correlation with the surface curvature are explored using DNS data. The scalar gradient alignment characteristics change from aligning with the most compressive strain to aligning with the most extensive one in regions of intensive heat release. This alignment change creates negative normal strain rate which can result in negative surface averaged tangential strain rate. The partial premixing affects the flame surface displacement speed through the mixture fraction dissipation rate and a second derivative in the mixture fraction space. The correlation of curvature and displacement speed is found to be negative in general and the effects of partial premixing act to reduce this negative correlation. The combined effects of the normal strain rate and the displacement speed/curvature correlation contribute to the negative mean flame stretch observed in the flame brush. Scalar dissipation rates (SDR) of the mixture fraction ẼZZ, progress variable Ẽcc and their cross dissipation rates (CDR) ẼcZ are identified as important quantities in the modelling of partially premixed flames. Their behaviours in the lifted flame stabilisation region are examined in a unified framework. It is found that SDR of mixture fraction is well below the quenching value in this region while SDR of progress variable is smaller than that in laminar flames. The CDR changes from weakly positive to negative at the flame leading edge due to the change in scalar gradient alignment characteristics. Axial and radial variation of these quantities are analysed and it is found that Ẽcc is an order of magnitude bigger than ẼZZ. ẼcZ is two orders of magnitude smaller than Ẽcc and it can be either positive or negative depending on local flow and flame conditions. Simple algebraic models show reasonable agreement compared to DNS when a suitable definition of c is used. Further statistics of the scalar gradients are presented and a presumed lognormal distribution is found to give reasonable results for their marginal PDFs and a bivariate lognormal distribution is a good approximation for their joint PDF. Four mean reaction rate closures based on presumed PDF and flamelets are assessed a priori using DNS data. The turbulent flame front structure is first compared with unstrained and strained laminar premixed and dif fusion flamelets. It is found that unstrained premixed flamelets give overall reasonable approximation in most parts of this flame. A joint PDF model which includes the correlation between mixture fraction and progress variable using a "copula" method shows excellent agreement with DNS results while their statistical independence does not hold in the burning regions of this partially premixed flame. The unstrained premixed flamelet with the correlated joint PDF method is identified to be the most appropriate model for the lifted jet flame calculation. This model is then used in the RANS simulation of turbulent jet lifted flames. A new model to include the contribution from diffusion burning and the effects of partial premixing due to SDR of mixture fraction is also identified and included in the calculation. These models are implemented in a commercial CFD code "Fluent" with user defined scalars and functions. It is found that both the correlated joint PDF model and the model accounting for the diffusive burning in partial premixing are important in order to accurately predict flame lift-off height compared to the experiments.
Author : Celine D. Kluzek
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (689 download)
Download or read book Structure of Partially Premixed Flames Using Detailed Chemistry Simulations written by Celine D. Kluzek and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: State-of-the-art reacting-flow computations have to compromise either on the detail of chemical reactions or on the dimensionality of the solution, while experiments in flames are limited by the flow accessibility and provide at best a limited number of observables. In the present work, the partially premixed laminar flame structure is examined using a detailed-chemistry, one-dimensional simulation. The computational results are compared to unpublished single-point multiscalar measurements obtained at Sandia National Labs in 2001. The study is focused on axisymmetric laminar partially-premixed methane/air flames with varying premixture strength values of 1.8, 2.2, and 3.17. The combination of computational and experimental results is used to analyze the spatial and scalar flame structure under the overarching concept of flamelets. The computations are based on the Cantera open-source software package developed at CalTech by D. Goodwin, and incorporating the GRI 3.0 chemical kinetic mechanism utilizing 325 chemical reactions and 53 species for methane combustion. Cross-transport effects as well as an optically-thin radiation model are included in the calculations. Radiation changes the flame profiles due to its effect on temperature, and the attendant effects on a number of species. Using the detailed analysis of different reaction rates, the adiabatic and radiative nitric oxide concentrations are compared. The cross-transport effects, i.e. Soret and Dufour, were studied in detail. The Soret term has a small but important effect on the flame structure through a reduction of the hydrogen mass fraction, which changes the conserved scalar values. Based on the flamelet approach and a unique formulation of the conserved scalar, the flame thermochemistry can be analyzed and understood. A number of interesting effects on the flame thermochemistry can be discerned in both experiments and computations when the premixture strength is varied. An increase in premixing results in a counterintuitive decrease in intermediate species such as carbon monoxide and hydrogen, as well as an expected increase in nitric oxide concentrations. Good agreement is found between experiments and calculations in scalar space, while the difference in dimensionality between axisymmetric measurements and opposed jet computations makes comparison in physical space tentative.
Author : Daniele Dovizio
Publisher :
ISBN 13 :
Total Pages : 156 pages
Book Rating : 4.:/5 (926 download)
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.
Download or read book Assessment of Flame Kernel Propagation in Partially Premixed Turbulent Jet Under Different Turbulence Levels written by and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : K. Sun
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (11 download)
Download or read book A Computational and Experimental Study of Turbulent Partially Premixed Jet Flames written by K. Sun and published by . This book was released on 1995 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Han Shen
Publisher :
ISBN 13 :
Total Pages : 65 pages
Book Rating : 4.:/5 (922 download)
Download or read book Characterization of the Structure of Turbulent Non-premixed Dimethyl Ether Jet Flames written by Han Shen and published by . This book was released on 2015 with total page 65 pages. Available in PDF, EPUB and Kindle. Book excerpt: The second set of experimental results is derived from a research collaboration with Sandia National Laboratories to compare direct numerical simulation (DNS) of a temporally-evolving jet flame with experimental measurements from a spatially-evolving jet flame operating under identical Reynolds and Damkohler numbers with significant levels of local flame extinction. Simultaneous OH/CH2O (formaldehyde) PLIF imaging is performed to characterize the spatial structure of the turbulent DME flames, where the OH PLIF imaging yields information regarding the high-temperature reactive layer structure and the CH2O PLIF imaging yields information regarding the low-temperature, partial oxidation structure. First, the structure of the flames is in qualitative agreement, displaying similar extinction and re-ignition patterns in both the DNS and the experiments. Joint OH/CH2O statistics from the DNS and the experiments are found to agree very well indicating a strong anti-correlation between OH and CH2O. As one example, an alignment index defined in terms of the OH and CH2O gradients was computed from both DNS and experimental results. For both DNS and experimental results, the probability density function (PDF) of the alignment index peaked at -1 at all time (DNS) and spatial (experiments) instances, indicating that the gradients of OH and CH2O are opposed, even under very low Damkohler number conditions. Finally, the [OH] x [CH2O] product imaging is evaluated as a surrogate for peak heat release rate and is found to be an excellent surrogate of the peak heat release rate in the DNS results. This agreed qualitatively with observed experimental results that showed that the OH and CH2O PLIF images overlapped only in very small spatial regions, presumably demarcating the regions between fuel oxidation and primary heat release. This result is consistent with the statistical results of the alignment index that indicate that the OH and CH2O gradients are opposed, i.e., as CH2O is consumed, OH is formed. The OH/CH2O product imaging which is used to predict peak hear release rate agrees with the simulation extremely well.
Author : Sastri Purushottama Nandula
Publisher :
ISBN 13 :
Total Pages : 364 pages
Book Rating : 4.:/5 (55 download)
Download or read book Lean Premixed Flame Structure in Intense Turbulence written by Sastri Purushottama Nandula and published by . This book was released on 2003 with total page 364 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : MING-SHIN WU
Publisher :
ISBN 13 :
Total Pages : 376 pages
Book Rating : 4.3/5 (91 download)
Download or read book THE SURFACE STRUCTURE OF TURBULENT PREMIXED HYDROGEN/AIR RIM-STABILIZED FLAMES AT HIGH REYNOLDS NUMBER (PREMIXED TURBULENT FLAMES, FLAMES). written by MING-SHIN WU and published by . This book was released on 1991 with total page 376 pages. Available in PDF, EPUB and Kindle. Book excerpt: three-dimensional simulation, to remove 2-D deficiencies, appears to be computationally feasible for high Reynolds number conditions of interest for practical applications.
Author : Rodney O. Fox
Publisher : Cambridge University Press
ISBN 13 : 9780521659079
Total Pages : 156 pages
Book Rating : 4.6/5 (59 download)
Download or read book Computational Models for Turbulent Reacting Flows written by Rodney O. Fox and published by Cambridge University Press. This book was released on 2003-10-30 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: Table of contents
Author : D. Feikema
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (11 download)
Download or read book Vizualisation of the Structure of Premixed Turbulent Flames written by D. Feikema and published by . This book was released on 1989 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
