Table Of ContentDiss. ETH Nr. 14947
Numerical investigation of turbulent
nonpremixed methane-air flames
A dissertation submitted to the
EIDGENÖSSISCHE TECHNISCHE HOCHSCHULE ZÜRICH
for the degree of
Doctor of Technical Sciences
Presented by
LALE DEMIRAYDIN
Diplom Ingenieur (Masch.)
Technical University of Istanbul
born June 28th, 1974
Citizen of Turkey
Accepted on the recommendation of
Prof. Dr. D. Poulikakos, examiner
Prof. Dr. K. Boulouchos, co-examiner
Dr. J. Gass, co-examiner
Zurich, 2002
To my Parents
NURSEL and AYDIN
Those were the days...
Once upon a time there was a tavern,
Where we used to raise a glass or two.
Remember how we laughed away the hours.
And dreamed of all the great things we would do.
Those were the days, my friend
We thought they would never end.
We'd sing and dance forever and a day.
We'd live the life we choose
We'd fight and never lose
For we were young and sure to have our way.
Lalala lah lala, Lalala lah lala
Then the busy years went rushing by us,
We lost our starry notions on the way.
If by chance I'd see you in the tavern,
We'd smile at one another and we'd say:
Those were the days, my friend
We thought they would never end
We'd sing and dance forever and a day.
We'd live the life we choose
We'd fight and never lose
Those were the days, my friend. Those were the days.
Just tonight I stood before the tavern,
Nothing seemed the way it used to be.
In the glass I saw a strange reflection.
Was that lonely person really me?
Through the door there came familiar laughter.
I saw your face and heard you call my name.
Oh, my friend! We are older but no wiser,
For in our hearts the dreams are still the same...
a traditional Russian folk song adapted by G. Raskin
Acknowledgements
This research project is accomplished in Laboratory of Thermodynamics in Emerging
Technologies (LTNT) at ETH-Zürich with the help and support of many people.
Above all, I wish to express my sincere thanks to Prof. Dimos Poulikakos for his invaluable
help and his steadfast support. I am also thankful to Prof. Konstantinos Boulouchos for his
agreement to become a correferent and his helpful comments on the draft of this dissertation. I
thank Dr. Jürg Gass for indoctrinating me into the way of combustion science, for his technical
support and for his encouragement during these years. For the financial support of this work, I
sincerely thank Dr. Alphons Hintermann from the Federal Office of Energy, Switzerland.
I am grateful to Dr. Andreas Obieglo for adapting me to the research environment in LTNT, for
guiding me in my work and for his friendship. This work has benefited greatly from the input of
Dr. Armin Laxander and Dr. George Ferreira, who were former members of our combustion
group. I am thankful to them. I am also thankful to Dr. Christos Frouzakis from ETH Zürich,
Dr. Epaminondas Mastorakos from Cambridge University Engineering Department, Prof. Ali
C. Benim from Fachhochschule Düsseldorf, Prof. Dirk Roekarts from TU Delft, Prof. Luc
Vervisch from INSA de Rouen France, who were always ready to share their knowledge with
me. I also want to thank Dr. Rob Barlow, from Sandia National Laboratories CA, who provided
the experimental data and Prof. Rodney Fox, Dr. Kochen Tsai and Raman Venkatramanan who
provided the GIEM routines. I would like to thank our system administrators, especially, Tonko
Racic for his effort to keep the system always running and Tilo Steiger for his support to any
problem in the computer systems.
I would like to thank all the members of LTNT, especially to the people of the combustion
group Dr. Christian Deltaglia, Dr. Pankaj Bajaj, Sevket Baykal, Lars Blum and Andrea
Prospero, for their technical help and for providing a friendly environment.
Many special thanks go to the great people, who were -far beyond being colleagues or friends-
my family in Zurich: Dr. Andreas Chaniotis for the helpful discussions about my work and for
his precious company during those years. Salvatore Arcidiacono for always being there to listen
the birds with me and watch the shiny sky. Marco Simiano for always bringing me the happiness
and joy. Dr. Stavros Tsantilis for uncountable number of nice times we spent, dinners we had,
vacations we did and a last-minute idea he gave. Mathias Dietzel for being a sincere friend,
sharing the nice times, standing my crazy actions and being the chief-architect of my marvellous
‘Doktorhut’. Arriving late to my world in Zurich, but taking their important positions in my life:
Sandro De Gruttola for always being smiling, Sevket Baykal for the best advices, friendly
solaces, greatest comments, and delicious desserts. Iordanis Chatziprodromou -the description
of ‘amity’- for the most friendly conversations. Evangelos Boutsianis for teaching me the
meaning of perfection. With all of you, I lived the best times of my life in the last three years.
I also thank Evren Alper for once being the sunset in the horizon, that I let the boat sail towards.
Last but not least, I thank my father Aydin, my mother Nursel, my sister Eda and my aunt Nimet
for always believing me, supporting me in my way and motivating me to rise up in the life. I
dedicate my thesis to them.
Lale Demiraydin
Zürich, Switzerland
December 2002
Abstract
Turbulent combustion is an important phenomenon in industrial applications, such as
gas turbines, diesel engines, low NOx burners, spark-ignition engines and furnaces.
Improvements are often necessary, since the applications have to be effective,
economical and clean. Therefore, a better understanding of the turbulent combustion is
needed. Numerical simulations, so-called Computational Fluid Dynamics (CFD), help
to optimize and improve the applications in reacting flows. In comparison with
experimental studies, CFD is relatively cheap. Although a complete simulation of a
turbulent reacting flow, which involves all physical phenomena is not possible at
present, the solutions of CFD is able to facilitate the device-scale analysis and the
design of many new industrial combustion applications. The study of turbulent
combustion is important from a scientific point of view as from a practical point of
view. The use of the numerical models for industrial applications are first handled with
a continuous cycle of ‘the understanding of fundamentals of combustion’, ‘model
developments’, ‘implementation of models in numerical simulations’, and ‘validation of
the numerical results with experimental measurements’. When validating the numerical
models, simple flame configurations are required. This fact brings the importance of
studying the turbulent jet flows numerically and experimentally.
Turbulent combustion research can be classified into two categories: non-premixed
combustion and premixed combustion. In general, different modeling approaches are
required to deal with each combustion category. New generation low emission/low fuel
consumption combustion systems are characterized by a combined concept of two
combustion categories, which is called partially premixed turbulent combustion. For
example, lean premixed combustion systems for reducing NO emissions in gas turbine
x
combustors and gasoline direct injection spark-ignition engines for reducing the fuel
consumption operate in partially premixed conditions.
This work deals with the modeling of nonpremixed and partially premixed turbulent
combustion. The two common models of nonpremixed combustion are the probability
density function (PDF) transport equation models and laminar flamelet models. These
models have their own advantages and disadvantages. The PDF transport equation
models have the important advantage that the chemical source term appears in closed
form. Additionally, the statistical distributions of scalar variables are obtained by
calculated probability distributions. The laminar flamelet models have the advantage of
strong coupling between chemical reaction and molecular transport. The nonpremixed
combustion is classified into different regimes, depending on the flame structure. In
evaluating the regime of applicability, the PDF transport equation models and the
laminar flamelet models are disjoint. Since the molecular transport term requires
modeling in the PDF transport equation, the tight statistical correlation between
chemical activity and molecular transport is not considered in the PDF transport
equation models. This is a constraint for the model. Therefore, PDF transport equation
models are valid only when the turbulent mixing will still be sufficiently intense to
restrain the formation of coherent structures with correlated chemical kinetics. On the
other hand, when the turbulence intensities decrease, the interaction between chemical
reaction and molecular transport gains importance. This regime is called flamelet
regime and the laminar flamelet models are valid for this regime. The most promising
approach in this direction appears to be extending the PDF methods that would properly
account for the coupling between reaction and molecular transport in the flamelet
regime. Therefore, the present work was focused on a new concept, combining two
common types of non-premixed combustion models: the Eulerian composition PDF
transport equation models and transient laminar flamelet models. The new model -the
coupled TLFM/PDF model- aims to combine the advantages of the both models, while
avoiding their disadvantages. The compromise here is to solve the conserved scalar –the
mixture fraction- with the PDF transport equation and avoid using presumed PDF
shapes as in the laminar flamelet models. The scalar dissipation rate, reaction progress
variable and the turbulent time scale are the other decisive parameters, which are
calculated. Then, the thermochemical variables; such as temperature and mass fractions
of species are read from the transient flamelet libraries. The flamelet libraries consider
for the correlation of chemistry and molecular transport. The scalar dissipation rate
determines the extinction and the reaction progress variable determines the partially
premixed conditions.
The first stage of the study was to improve the transient laminar flamelet model of
Ferreira (ETH,Zürich) and validate the PDF transport equation model with a 4-step
reduced mechanism. The studies are applied to piloted jet flames, which are the target
flames of an international workshop. The velocity, mixture fraction, temperature and
mass fraction of species are evaluated. The second stage was to validate the new model,
-the coupled TLFM/PDF model- for the same test case and compare with the existing
models, which are mentioned above. The capabilities of each model, their advantages
and disadvantages are summarized. An additional study was the numerical study of an
opposed jet flame with the PDF transport equation model.
