Discrepancies between rig tests and numerical predictions of the flutter boundary for fan blades are usually attributed to the deficiency of computational fluid dynamics (CFD) models for resolving flow at off-design conditions. However, as will be demonstrated in this paper, there are a number of other factors, which can influence the flutter stability of fan blades and lead to differences between measurements and numerical predictions. This research was initiated as a result of inconsistencies between the flutter predictions of two rig fan blades. The numerical results agreed well with rig test data in terms of flutter speed and nodal diameter (ND) for both fans. However, they predicted a significantly higher flutter margin for one of the fans, while measured flutter margins were similar for both blades. A new set of flutter computations including the whole low-pressure system was therefore performed. The new set of computations considered the effects of the acoustic liner and mistuning for both blades. The results of this work indicate that the previous discrepancies between CFD and tests were caused by, first, differences in the effectiveness of the acoustic liner in attenuating the pressure wave created by the blade vibration and second, differences in the level of unintentional mistuning of the two fan blades. In the second part of this research, the effects of blade mis-staggering and inlet temperature on aerodynamic damping were investigated. The data presented in this paper clearly show that manufacturing and environmental uncertainties can play an important role in the flutter stability of a fan blade. They demonstrate that aeroelastic similarity is not necessarily achieved if only aerodynamic properties and the traditional aeroelastic parameters, reduced frequency and mass ratio, are maintained. This emphasizes the importance of engine-representative models, in addition to accurate and validated CFD codes, for the reliable prediction of the flutter boundary.

References

References
1.
Lane
,
F.
,
1956
, “
System Mode Shapes in the Flutter of Compressor Blade Rows
,”
J. Aeronaut. Sci.
,
23
(
1
), pp.
54
66
.
2.
Carta
,
F. O.
,
1967
, “
Coupled Blade-Disk-Shroud Flutter Instabilities in Turbojet Engine Rotors
,”
J. Eng. Power
,
89
(
3
), pp.
419
426
.
3.
Jeffers
,
J.
, and
Meece
,
C.
,
1975
, “
F100 Fan Stall Flutter Problem Review and Solution
,”
J. Aircr.
,
12
(
4
), pp.
350
357
.
4.
Chi
,
R.
, and
Srinivasan
,
A.
,
1985
, “
Some Recent Advances in the Understanding and Prediction of Turbomachine Subsonic Stall Flutter
,”
ASME J. Eng. Gas Turbines Power
,
107
(
2
), pp.
408
417
.
5.
Marshall
,
J.
, and
Imregun
,
M.
,
1996
, “
A Review of Aeroelasticity Methods With Emphasis on Turbomachinery Applications
,”
J. Fluids Struct.
,
10
(
3
), pp.
237
267
.
6.
Srinivasan
,
A. V.
,
1997
, “
Flutter and Resonant Vibration Characteristics of Engine Blades
,”
ASME J. Eng. Gas Turbines Power
,
119
(
4
), pp.
742
775
.
7.
Khalak
,
A.
,
2002
, “
A Framework for Flutter Clearance of Aeroengine Blades
,”
ASME J. Eng. Gas Turbines Power
,
124
(
4
), pp.
1003
1010
.
8.
Isomura
,
K.
, and
Giles
,
M.
,
1998
, “
A Numerical Study of Flutter in a Transonic Fan
,”
ASME J. Turbomach.
,
120
(
3
), pp.
500
507
.
9.
di Mare
,
L.
,
Vadati
,
M.
,
Mueck
,
B.
,
Smith
,
N. H.
, and
Birch
,
N.
,
2009
, “
Aeroelastic Instability of Fan Blades at High Altitudes
,”
ASME
Paper No. GT2009-60091.
10.
Vahdati
,
M.
, and
Cumpsty
,
N.
,
2015
, “
Aeroelastic Instability in Transonic Fans
,”
ASME J. Eng. Gas Turbines Power
,
138
(
2
), p.
022604
.
11.
Panovsky
,
J.
, and
Kielb
,
R. E.
,
1998
, “
A Design Method to Prevent Low Pressure Turbine Blade Flutter
,”
ASME
Paper No. 98-GT-575.
12.
Sayma
,
A. I.
,
Vahdati
,
M.
, and
Imregun
,
M.
,
2000
, “
An Integrated Non Linear Approach for Turbomachinery Forced Response Prediction—Part 1: Formulation
,”
J. Fluids Struct.
,
14
(
1
), pp.
87
101
.
13.
Lee
,
K.-B.
,
Wilson
,
M.
, and
Vahdati
,
M.
,
2016
, “
Numerical Study on Aeroelastic Instability for a Low Speed Fan
,”
ASME
Paper No. GT2016-56462.
14.
Salles
,
L.
, and
Vahdati
,
M.
,
2016
, “
Comparison of Two Numerical Algorithms for Computing the Effects of Mistuning of Fan Flutter
,”
ASME
Paper No. GT2016-57324.
15.
Vahdati
,
M.
,
Smith
,
N.
, and
Zhao
,
F.
,
2015
, “
Influence of Intake on Fan Blade Flutter
,”
ASME J. Turbomach.
,
137
(
8
), p.
081002
.
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