“Rumble” is a self-excited combustion instability, usually occurring at the start-up of aero-engines with fuel-spray atomizers at sub-idle and idle conditions, and exhibiting low limit frequencies in the range of 50Hzto150Hz. Entropy waves at the (nearly) choked combustor outlet are supposed to be the key feedback mechanism for the observed self-excited pressure oscillations. The experimental study presented here aims at clarifying the role of entropy waves in the occurrence of rumble. A generic air-blast atomizer with a design prone to self-excitation has been incorporated into a thermoacoustic combustor test rig with variable outlet conditions. The thermoacoustic response of the flame was characterized by recording the OH* chemiluminescence, the dynamic pressures, the dynamic temperatures, and by applying PIV. The measurements have shown the occurrence of periodic hot spots traveling with the mean flow with considerable dispersion. Measurements have been conducted with an open-ended resonance tube in order to eliminate the impact of entropy waves on the mechanism of self-excitation. The oscillation obtained, comparable in amplitude and frequency, proved that self-excitation primarily depends on convective time delays of the droplets in the primary zone and thus on the atomization characteristics of the nozzle.

1.
Keller
,
J. J.
, 1975, “
Thermoacoustic Oscillations in Combustion Chambers of Gas Turbines
,”
AIAA J.
0001-1452,
33
, pp.
2280
2287
.
2.
Lieuwen
,
T.
,
Torres
,
H.
,
Johnson
,
C.
, and
Zinn
,
B. T.
, 1999, “
A Mechanism of Combustion Instability in Lean Premixed Gas Turbine Combustors
,” ASME Paper No. 99-G-3.
3.
Marble
,
F. E.
, and
Candel
,
S. M.
, 1977, “
Acoustic Disturbance from Gas Non-Uniformities Convected Through a Nozzle
,”
J. Sound Vib.
0022-460X,
55
, pp.
225
243
.
4.
Polifke
,
W.
,
Paschereit
,
C. O.
, and
Döbbeling
,
K.
, 2001, “
Constructive and Destructive Interference of Acoustic and Entropy Waves in a Premixed Combustor With a Choked Exit
,”
Int. J. Acoust. Vib.
1027-5851,
6
, pp.
135
146
.
5.
Konrad
,
W.
,
Brehm
,
N.
,
Kameier
,
F.
,
Freeman
,
C.
, and
Day
,
I. J.
, 1998, “
Combustion Instability Investigations on the BR710 Jet Engine
,”
J. Eng. Gas Turbines Power
0742-4795,
120
, pp.
34
40
.
6.
Zhu
,
M.
,
Dowling
,
A. P.
, and
Bray
,
K. N. C.
, 2000, “
Self-Excited Oscillations in Combustors With Spray Atomizers
,” ASME Paper No. 2000-GT-0108.
7.
Sattelmayer
,
T.
, 2003, “
Influence of the Combustor Aerodynamics on Combustion Instabilities From Equivalence Ratio Fluctuations
,”
J. Eng. Gas Turbines Power
0742-4795,
125
, pp.
11
19
.
8.
Eckstein
,
J.
,
Freitag
,
E.
,
Hirsch
,
C.
,
Sattelmayer
,
T.
,
von der Bank
,
R.
, and
Schilling
,
T.
, 2005, “
Forced Low-Frequency Spray Characteristics of a Generic Airblast Swirl Diffusion Burner
,”
J. Eng. Gas Turbines Power
0742-4795,
127
, pp.
301
306
.
9.
Heilos
,
A.
, 2002, “
Spektrale Analyse der thermischen Strahlungswechselwirkung in Kohlenwasserstoffflammen
,” Berichte aus der Energietechnik, Shaker, 2002.
10.
Turns
,
S.
, 2000, “
An Introduction to Combustion: Concepts and Applications
,”
McGraw-Hill Series in Mechanical Engineering
,
2nd ed.
,
McGraw-Hill
, New York.
11.
Sujith
,
R. I.
,
Waldherr
,
G. A.
,
Jagoda
,
J. I.
, and
Zinn
,
B. T.
, 2000, “
Experimental Investigation of the Evaporation of Droplets in Axial Acoustic Fields
,”
J. Propul. Power
0748-4658,
16
, pp.
278
285
.
You do not currently have access to this content.