Table Of ContentUniversity of Iowa
Iowa Research Online
Theses and Dissertations
2008
Combustion dynamics of swirl-stabilized lean
premixed flames in an acoustically-driven
environment
Yun Huang
University of Iowa
Copyright 2008 Yun Huang
This dissertation is available at Iowa Research Online: https://ir.uiowa.edu/etd/203
Recommended Citation
Huang, Yun. "Combustion dynamics of swirl-stabilized lean premixed flames in an acoustically-driven environment." PhD (Doctor of
Philosophy) thesis, University of Iowa, 2008.
https://doi.org/10.17077/etd.090bzroh
Follow this and additional works at:https://ir.uiowa.edu/etd
Part of theMechanical Engineering Commons
COMBUSTION DYNAMICS OF SWIRL-STABILIZED LEAN PREMIXED FLAMES
IN AN ACOUSTICALLY-DRIVEN ENVIRONMENT
by
Yun Huang
An Abstract
Of a thesis submitted in partial fulfillment
of the requirements for the Doctor of
Philosophy degree in Mechanical Engineering
in the Graduate College of
The University of Iowa
December 2008
Thesis Supervisor: Assistant Professor Albert Ratner
1
ABSTRACT
Combustion instability is a process which involves unsteady chemical kinetic,
fluid mechanic, and acoustic processes. It can lead to unstable behavior and be
detrimental in ways ranging from faster part fatigue to catastrophic system failure. In
terms of combustion methodology, combustion instability has been a key issue for lean
premixed combustion. The primary objective of this work is to improve understanding of
combustion dynamics through an experimental study of lean premixed combustion using
a low swirl combustor. This special burner was developed at the Lawrence Berkeley
National Laboratory and has recently received significant interest from the gas turbine
industry.
In these experiments, acoustic perturbations (chamber modes) are imposed on a
low swirl stabilized methane-air flame using loudspeakers. The flame response is
examined and quantified with OH planar laser induced fluorescence. Rayleigh index
maps of the flame are computed for each frequency and operating condition. Examining
the structures in the Rayleigh maps, it is evident that, while the flame shows no
significant response in some cases, acoustic forcing in the 70-150 Hz frequency range
induces vortex shedding in the flame shear layer. These vortices distort the flame front
and generate locally compact and sparse flame areas. This information about the flow
field shows that, besides illuminating the combustion dynamics, the Rayleigh index is a
useful way to reveal interesting aspects of the underlying flow.
The experiments also revealed other interesting aspects of this flame system. It
was found that the flame becomes unstable when the perturbation amplitude reaches
0.7% of the mean pressure. Decreasing the swirl number makes the flame shape more jet-
like, but does little to alter the shear-layer coupling. In a similar fashion, increasing the
pressure was found to alter the flame shape and flame extent, but the thermo-acoustic
2
coupling and induced large scale structure persisted to 0.34MPa, the highest pressure
tested.
Abstract Approved: ____________________________________
Thesis Supervisor
____________________________________
Title and Department
____________________________________
Date
COMBUSTION DYNAMICS OF SWIRL-STABILIZED LEAN PREMIXED FLAMES
IN AN ACOUSTICALLY-DRIVEN ENVIRONMENT
by
Yun Huang
A thesis submitted in partial fulfillment
of the requirements for the Doctor of
Philosophy degree in Mechanical Engineering
in the Graduate College of
The University of Iowa
December 2008
Thesis Supervisor: Assistant Professor Albert Ratner
Copyright by
YUN HUANG
2008
All Rights Reserved
Graduate College
The University of Iowa
Iowa City, Iowa
CERTIFICATE OF APPROVAL
_______________________
PH.D. THESIS
_______________
This is to certify that the Ph.D. thesis of
Yun Huang
has been approved by the Examining Committee
for the thesis requirement for the Doctor of Philosophy
degree in Mechanical Engineering at the December 2008 graduation.
Thesis Committee: ___________________________________
Albert Ratner, Thesis Supervisor
___________________________________
James Buchholz
___________________________________
P. Barry Butler
___________________________________
Lea-Der Chen
___________________________________
Ching-Long Lin
___________________________________
Charles Stanier
To Shuiqing and Jonathan
ii
ACKNOWLEDGEMENTS
First, I would like to express my sincere gratitude to my advisor, Professor Albert
Ratner, for all of his help and support throughout my PhD study in Iowa. His guidance,
understanding and encouragement have provided a foundation for the present thesis.
I would like to express my sincere thanks to my thesis committee members, Prof.
James Buchholz, Prof. P. Barry Butler, Prof. Lea-Der Chen, Prof. Ching-Long Lin and
Prof. Charles Stanier. I learned much about being a good professor by learning in your
classes, working as teaching assistant, and getting advices on my research and career
development.
I thank all the members in our lab; in particular, Dr. Dal Mo Kang, who taught me
the experimental techniques needed to carry out combustion instability research during
his visit; former graduate students Brett Bathel and Hui Gao for their support and their
help with the first portion of the experiments; Ilker Yilmaz and Majid Emadi for helping
me with elevated pressure experiments; and Anthony Dix, Bihua Wei, Yongli Zhao,
Xinghui Zhang, Yan Zhang, Neeraj Kumar Mishra, Eric DeCristofaro, for making my
time here so enjoyable.
I am deeply grateful to Professor C.K. Law at Princeton University for providing
me the opportunity to study and learn in his laboratory during my summer visit. The
members of Prof. Law’s group also have my gratitude for their help and kindness during
my stay.
I would like to thank the University of Iowa, the Richard B. Stewart Thermal-
Fluids Graduate Scholarship foundation, the Lawrence Berkeley National Laboratory
(R.K. Cheng as the project monitor), and Siemens (Scott Martin as the project monitor),
for financial support.
Finally I want to thank my dearest family for their love and encouragement.
iii
ABSTRACT
Combustion instability is a process which involves unsteady chemical kinetic,
fluid mechanic, and acoustic processes. It can lead to unstable behavior and be
detrimental in ways ranging from faster part fatigue to catastrophic system failure. In
terms of combustion methodology, combustion instability has been a key issue for lean
premixed combustion. The primary objective of this work is to improve understanding of
combustion dynamics through an experimental study of lean premixed combustion using
a low swirl combustor. This special burner was developed at the Lawrence Berkeley
National Laboratory and has recently received significant interest from the gas turbine
industry.
In these experiments, acoustic perturbations (chamber modes) are imposed on a
low swirl stabilized methane-air flame using loudspeakers. The flame response is
examined and quantified with OH planar laser induced fluorescence. Rayleigh index
maps of the flame are computed for each frequency and operating condition. Examining
the structures in the Rayleigh maps, it is evident that, while the flame shows no
significant response in some cases, acoustic forcing in the 70-150 Hz frequency range
induces vortex shedding in the flame shear layer. These vortices distort the flame front
and generate locally compact and sparse flame areas. This information about the flow
field shows that, besides illuminating the combustion dynamics, the Rayleigh index is a
useful way to reveal interesting aspects of the underlying flow.
The experiments also revealed other interesting aspects of this flame system. It
was found that the flame becomes unstable when the perturbation amplitude reaches
0.7% of the mean pressure. Decreasing the swirl number makes the flame shape more jet-
like, but does little to alter the shear-layer coupling. In a similar fashion, increasing the
pressure was found to alter the flame shape and flame extent, but the thermo-acoustic
coupling and induced large scale structure persisted to 0.34MPa, the highest pressure
tested.
iv
Description:Decreasing the swirl number makes the flame shape more jet- like, but does little to alter the shear-layer coupling. In a similar fashion, increasing the.
