Linear stability analysis is applied to a swirl-stabilized combustor flow with the aim to understand how the flame shape and associated density field affects the manifestation of self-excited flow instabilities. In isothermal swirling jets, self-excited flow oscillations typically manifest in a precessing vortex core and synchronized growth of large-scale spiral-shaped vortical structures. Recent theoretical studies relate these dynamics to a hydrodynamic global instability. These global modes also emerge in reacting flows, thereby crucially affecting the mixing characteristics and the flame dynamics. It is, however, observed that these self-excited flow oscillations are often suppressed in the reacting flow, while they are clearly present at isothermal conditions. This study provides strong evidence that the suppression of the precessing vortex core is caused by density inhomogeneities created by the flame. This mechanism is revealed by considering two reacting flow configurations: The first configuration represents a perfectly premixed steam-diluted detached flame featuring a strong precessing vortex core. The second represents a perfectly premixed dry flame anchoring near the combustor inlet, which does not exhibit self-excited oscillations. Experiments are conducted in a generic combustor test rig and the flow dynamics are captured using PIV and LDA. The corresponding density fields are approximated from the seeding density using a quantitative light sheet technique. The experimental results are compared to the global instability properties derived from hydrodynamic linear stability theory. Excellent agreement between the theoretically derived global mode frequency and measured precession frequency provide sufficient evidence to conclude that the self-excited oscillations are, indeed, driven by a global hydrodynamic instability. The effect of the density field on the global instability is studied explicitly by performing the analysis with and without density stratification. It turns out that the significant change in instability is caused by the radial density gradients in the inner recirculation zone and not by the change of the mean velocity field. The present work provides a theoretical framework to analyze the global hydrodynamic instability of realistic combustion configurations. It allows for relating the flame position and the resulting density field to the emergence of a precessing vortex core.

References

References
1.
Moeck
,
J. P.
,
Bourgouin
,
J.
,
Durox
,
D.
,
Schuller
,
T.
, and
Candel
,
S.
,
2012
, “
Nonlinear Interaction Between a Precessing Vortex Core and Acoustic Oscillations in a Turbulent Swirling Flame
,”
Combust. Flame
,
159
(
8
), pp. 2650–2668.10.1016/j.combustflame.2012.04.002
2.
Terhaar
,
S.
, and
Paschereit
,
C. O.
,
2012
, “
High-Speed PIV Investigation of Coherent Structures in a Swirl-Stabilized Combustor Operating at Dry and Steam-Diluted Conditions
,”
16th Int. Symp. on Applications of Laser Techniques to Fluid Mechanics Lisbon
,
Portugal
, July 9–12.
3.
Boxx
,
I.
,
Stöhr
,
M.
,
Carter
,
C. D.
, and
Meier
,
W.
,
2010
, “
Temporally Resolved Planar Measurements of Transient Phenomena in a Partially Pre-Mixed Swirl Flame in a Gas Turbine Model Combustor
,”
Combust. Flame
,
157
(
8
), pp.
1510
1525
.10.1016/j.combustflame.2009.12.015
4.
Fokaides
,
P.
,
Weiß
,
M.
,
Kern
,
M.
, and
Zarzalis
,
N.
,
2009
, “
Experimental and Numerical Investigation of Swirl Induced Self-Excited Instabilities at the Vicinity of an Airblast Nozzle
,”
Flow Turbulence Combust.
,
83
, pp.
511
533
.10.1007/s10494-009-9205-3
5.
Froud
,
D.
,
O'Doherty
,
T.
, and
Syred
,
N.
,
1995
, “
Phase Averaging of the Precessing Vortex Core in a Swirl Burner Under Piloted and Premixed Combustion Conditions
,”
Combust. Flame
,
100
(
3
), pp.
407
412
.10.1016/0010-2180(94)00167-Q
6.
Galley
,
D.
,
Ducruix
,
S.
,
Lacas
,
F.
, and
Veynante
,
D.
,
2011
, “
Mixing and Stabilization Study of a Partially Premixed Swirling Flame Using Laser Induced Fluorescence
,”
Combust. Flame
,
158
(
1
), pp.
155
171
.10.1016/j.combustflame.2010.08.004
7.
Syred
,
N.
,
2006
, “
A Review of Oscillation Mechanisms and the Role of the Precessing Vortex Core (PVC) in Swirl Combustion Systems
,”
Progr. Energy Combust. Sci.
,
32
(
2
), pp.
93
161
.10.1016/j.pecs.2005.10.002
8.
Giauque
,
A.
,
Selle
,
L.
,
Gicquel
,
L.
,
Poinsot
,
T.
,
Buechner
,
H.
,
Kaufmann
,
P.
, and
Krebs
,
W.
,
2005
, “
System Identification of a Large-Scale Swirled Partially Premixed Combustor Using LES and Measurements
,”
J. Turbulence
,
6
, p.
21
.10.1080/14685240512331391985
9.
Roux
,
S.
,
Lartigue
,
G.
,
Poinsot
,
T.
,
Meier
,
U.
, and
Bérat
,
C.
,
2005
, “
Studies of Mean and Unsteady Flow in a Swirled Combustor Using Experiments, Acoustic Analysis, and Large Eddy Simulations
,”
Combust. Flame
,
141
(
1–2
), pp.
40
54
.10.1016/j.combustflame.2004.12.007
10.
Liang
,
H.
, and
Maxworthy
,
T.
,
2005
, “
An Experimental Investigation of Swirling Jets
,”
J. Fluid Mech.
,
525
, pp.
115
159
.10.1017/S0022112004002629
11.
Oberleithner
,
K.
,
Sieber
,
M.
,
Nayeri
,
C. N.
,
Paschereit
,
C. O.
,
Petz
,
C.
,
Hege
,
H.-C.
,
Noack
,
B. R.
, and
Wygnanski
,
I.
,
2011
, “
Three-Dimensional Coherent Structures in a Swirling Jet Undergoing Vortex Breakdown: Stability Analysis and Empirical Mode Construction
,”
J. Fluid Mech.
,
679
, pp.
383
414
.10.1017/jfm.2011.141
12.
Oberleithner
,
K.
,
Paschereit
,
C. O.
,
Seele
,
R.
, and
Wygnanski
,
I.
,
2012
, “
Formation of Turbulent Vortex Breakdown: Intermittency, Criticality, and Global Instability
,”
AIAA J.
,
50
, pp.
1437
1452
.10.2514/1.J050642
13.
Ruith
,
M. R.
,
Chen
,
P.
,
Meiburg
,
E.
, and
Maxworthy
,
T.
,
2003
, “
Three-Dimensional Vortex Breakdown in Swirling Jets and Wakes: Direct Numerical Simulation
,”
J. Fluid Mech.
,
486
, pp.
331
378
.10.1017/S0022112003004749
14.
Gallaire
,
F.
,
Ruith
,
M.
,
Meiburg
,
E.
,
Chomaz
,
J.-M.
, and
Huerre
,
P.
,
2006
, “
Spiral Vortex Breakdown As a Global Mode
,”
J. Fluid Mech.
,
549
, pp.
71
80
.10.1017/S0022112005007834
15.
Monkewitz
,
P. A.
,
Bechert
,
D. W.
,
Barsikow
,
B.
, and
Lehmann
,
B.
,
1990
, “
Self-Excited Oscillations and Mixing in a Heated Round Jet
,”
J. Fluid Mech.
,
213
, pp.
611
639
.10.1017/S0022112090002476
16.
Gaster
,
M.
,
Kit
,
E.
, and
Wygnanski
,
I.
,
1985
, “
Large-Scale Structures in a Forced Turbulent Mixing Layer
,”
J. Fluid Mech.
,
150
, pp.
23
39
.10.1017/S0022112085000027
17.
Noack
,
B. R.
,
Afanasiev
,
K.
,
Morzyński
,
M.
,
Tadmor
,
G.
, and
Thiele
,
F.
,
2003
, “
A Hierarchy of Low-Dimensional Models for the Transient and Post-Transient Cylinder Wake
,”
J. Fluid Mech.
,
497
, 335–363.10.1017/S0022112003006694
18.
Pier
,
B.
,
2002
, “
On the Frequency Selection of Finite-Amplitude Vortex Shedding in the Cylinder Wake
,”
J. Fluid Mech.
,
458
, pp.
407
417
.10.1017/S0022112002008054
19.
Barkley
,
D.
,
2006
, “
Linear Analysis of the Cylinder Wake Mean Flow
,”
EPL (Europhys. Lett.)
,
75
, pp.
750
756
.10.1209/epl/i2006-10168-7
20.
Lesshafft
,
L.
, and
Marquet
,
O.
,
2010
, “
Optimal Velocity and Density Profiles for the Onset of Absolute Instability in Jets
,”
J. Fluid Mech.
,
662
, pp.
398
408
.10.1017/S0022112010004246
21.
Oberleithner
,
K.
,
Schimek
,
S.
, and
Paschereit
,
C. O.
,
2012
, “
On the Impact of Shear Flow Instabilities on Global Heat Release Rate Fluctuations: Linear Stability Analysis of an Isothermal and a Reacting Swirling Jet
,”
ASME
Paper No. GT2012-69774.10.1115/GT2012-69774
22.
Hussain
,
A. K. M. F.
, and
Reynolds
,
W. C.
,
1970
, “
The Mechanics of an Organized Wave in Turbulent Shear Flow
,”
J. Fluid Mech.
,
41
, pp.
241
258
.10.1017/S0022112070000605
23.
Lesshafft
,
L.
,
2006
, “
Nonlinear Global Modes and Sound Generation in Hot Jets
,” Ph.D. thesis, Ecole Polytechnique, Palaiseau, France.
24.
Michalke
,
A.
,
1965
, “
On Spatially Growing Disturbances in an Inviscid Shear Layer
,”
J. Fluid Mech.
,
23
, pp.
521
544
.10.1017/S0022112065001520
25.
Juniper
,
M. P.
,
Tammisola
,
O.
, and
Lundell
,
F.
,
2011
, “
The Local and Global Stability of Confined Planar Wakes at Intermediate Reynolds Number
,”
J. Fluid Mech.
,
686
, pp.
218
238
.10.1017/jfm.2011.324
26.
Provansal
,
M.
,
Mathis
,
C.
, and
Boyer
,
L.
,
1987
, “
Benard-von Karman Instability: Transient and Forced Regimes
,”
J. Fluid Mech.
,
182
, pp.
1
22
.10.1017/S0022112087002222
27.
Monkewitz
,
P. A.
,
1988
, “
The Absolute and Convective Nature of Instability in Two-Dimensional Wakes at Low Reynolds Numbers
,”
Phys. Fluids
,
31
, pp.
999
1006
.10.1063/1.866720
28.
Huerre
,
P.
, and
Monkewitz
,
P. A.
,
1990
, “
Local and Global Instabilities in Spatially Developing Flows
,”
Annu. Rev. Fluid Mech.
,
22
, pp.
473
537
.10.1146/annurev.fl.22.010190.002353
29.
Briggs
,
R., J.
,
1964
,
Electron-Stream Interaction With Plasmas
,
MIT Press
,
Cambridge, MA
.
30.
Sipp
,
D.
, and
Lebedev
,
A.
,
2007
, “
Global Stability of Base and Mean Flows: A General Approach and Its Applications to Cylinder and Open Cavity Flows
,”
J. Fluid Mech.
,
593
, pp.
333
358
.10.1017/S0022112007008907
31.
Theofilis
,
V.
,
2011
, “
Global Linear Instability
,”
Annu. Rev. Fluid Mech.
,
43
, pp.
319
352
.10.1146/annurev-fluid-122109-160705
32.
Chomaz
,
J.
,
Huerre
,
P.
, and
Redekopp
,
L. G.
,
1991
, “
A Frequency Selection Criterion in Spatially Developing Flows
,”
Studies Appl. Math.
,
84
, pp.
119–144
.
33.
Rees
,
S. R.
,
2009
, “
Hydrodynamic Instability of Confined Jets & Wakes and Implications for Gas Turbine Fuel Injectors
,” Ph.D. thesis, University of Cambridge, Cambridge, UK.
34.
Leuckel
,
W.
,
1967
, “
Swirl Intensities, Swirl Types and Energy Losses of Different Swirl Generating Devices
,” Tech. Rep., Doc. No. G02/a/16, International Flame Research Foundation, Ijmuiden, The Netherlands.
35.
Voigt
,
P.
,
Schodl
,
R.
, and
Griebel
,
P.
,
1997
, “
Using the Laser Light Sheet Technique in Combustion Research
,”
Proc. 90th Symp. of AGARD-PEP on Advanced Non-Intrusive Instrumentation for Propulsion Engines, Brussels, Belgium, October 20–24
.
36.
Findeisen
,
J.
,
Gnirß
,
M.
,
Damaschke
,
N.
,
Schiffer
,
H.-P.
, and
Tropea
,
C.
,
2005
, “
2D—Concentration Measurements Based on Mie Scattering Using a Commercial PIV System
,”
6th International Symposium on Particle Image Velocimetry, Pasadena
,
CA
, September 21–23, PIV''05 Paper.
37.
Roehle
,
I.
,
Schodl
,
R.
,
Voigt
,
P.
, and
Willert
,
C.
,
2000
, “
Recent Developments and Applications of Quantitative Laser Light Sheet Measuring Techniques in Turbomachinery Components
,”
Measure. Sci. Technol.
,
11
(
7
), pp.
1023
1035
.10.1088/0957-0233/11/7/317
38.
Berkooz
,
G.
,
Holmes
,
P.
, and
Lumley
,
J. L.
,
1993
, “
The Proper Orthogonal Decomposition in the Analysis of Turbulent Flows
,”
Annu. Rev. Fluid Mech.
,
25
, pp.
539
575
.10.1146/annurev.fl.25.010193.002543
39.
Monkewitz
,
P. A.
, and
Sohn
,
K. D.
,
1988
, “
Absolute Instability in Hot Jets
,”
AIAA J.
,
26
, pp.
911
916
.10.2514/3.9990
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