The three major aeroelastic issues in the turbomachinery blades of jet engines and power turbines are forced response, nonsynchronous vibrations, and flutter. Flutter primarily affects high-aspect ratio blades found in the fan, fore high-pressure compressor stages, and aft low-pressure turbine (LPT) stages as low natural frequencies and high axial velocities create smaller reduced frequencies. Often with LPT flutter analyses, physical insights are lost in the exhaustive quest for determining whether the aerodynamic damping is positive or negative. This paper underlines some well-known causes of the LPT flutter in addition to one novel catalyst. In particular, an emphasis is placed on revealing how local aerodynamic damping contributions change as a function of unsteady (e.g., mode shape, reduced frequency) and steady (e.g., blade torque, pressure ratio) parameters. To this end, frequency domain Reynolds-averaged Navier–Stokes (RANS) CFD analyses are used as computational wind tunnels to investigate how aerodynamic loading variations affect flutter boundaries. Preliminary results show clear trends between the aerodynamic work influence coefficients and variations in exit Mach number and back pressure, especially for torsional mode shapes affecting the passage throat. Additionally, visualizations of qualitative bifurcations in the unsteady pressure phases around the airfoil shed light on how local damping contributions evolve with steady loading. Final results indicate a sharp drop in aeroelastic stability near specific regions of the pressure ratio, indicating a strong correlation between blade loading and flutter. Passage throat shock behavior is shown to be a controlling factor near the trailing edge, and as with critical reduced frequency, this phenomenon is shown to be highly dependent on the vibratory mode shape.

References

References
1.
Panovsky
,
J.
, and
Kielb
,
R. E.
,
2000
, “
A Design Method to Prevent Low Pressure Turbine Blade Flutter
,”
ASME J. Eng. Gas Turbines Power
,
122
(
1
), pp.
89
98
.
2.
Vogt
,
D.
,
2005
, “
Experimental Investigation of Three-Dimensional Mechanisms in Low-Pressure Turbine Flutter
,”
Ph.D. thesis
, KTH Royal Institute of Technology, Stockholm, Sweden.
3.
Bendiksen
,
O.
, and
Friedmann
,
P.
,
1980
, “
Coupled Bending-Torsion Flutter in Cascades
,”
AIAA J.
,
18
(
2
), pp.
194
201
.
4.
Nowinski
,
M.
, and
Panovsky
,
J.
,
2000
, “
Flutter Mechanisms in Low Pressure Turbine Blades
,”
ASME J. Eng. Gas Turbines Power
,
122
(
1
), pp.
82
88
.
5.
Kirschner
,
A.
,
Pelet
,
C.
, and
Gyamarthy
,
G.
,
1976
, “
Investigation of Blade Flutter in a Subsonic Turbine
,” Revue Française de Mécanique, Numéro Spécial, pp.
97
104
.
6.
Tchernycheva
,
O. V.
,
Fransson
,
T.
,
Kielb
,
R. E.
, and
Barter
,
J.
,
2001
, “
Comparative Analysis of Blade Mode Shape Influence on Flutter of Two-Dimensional Turbine Blades
,” 15th International Symposium on Air Breathing Machines (
ISABE
), Bangalore, India, Sept. 3–7, ISABE Paper No. ISABE-2001-1243.
7.
Waite
,
J. J.
, and
Kielb
,
R. E.
,
2014
, “
Physical Understanding and Sensitivities of Low Pressure Turbine Flutter
,”
ASME J. Eng. Gas Turbines Power
,
137
(
1
), p.
012502
.
8.
Clark
,
S. T.
,
2013
, “
Design for Coupled-Mode Flutter and Non-Synchronous Vibration in Turbomachinery
,”
Ph.D. thesis
, Duke University, Department of Mechanical Engineering and Materials Science, Durham, NC.
9.
Kielb
,
R. E.
,
2001
, “
CFD for Turbomachinery Unsteady Flows—An Aeroelastic Design Perspective
,”
AIAA
Paper No. 2001-0429.
10.
Carta
,
F. O.
, and
Hilaire
,
A. O. St.
,
1980
, “
Effect of Interblade Phase Angle and Incidence Angle on Cascade Pitching Stability
,”
ASME J. Eng. Gas Turbines Power
,
102
(
2
), pp.
391
396
.
11.
Széchényi
,
E.
,
1985
, “
Fan Blade Flutter: Single Blade Instability or Blade to Blade Coupling?
,”
ASME
Paper No. 85-GT-216.
12.
Cardinale
,
V. M.
,
Bankhead
,
H. R.
, and
McKay
,
R. A.
,
1981
, “
Experimental Verification of Turboblading Aeromechanics
,”
56th Symposium of the AGARD Propulsion and Energetics Panel
, Turin, Italy, Sept. 29–Oct. 3.
13.
Zweifel
,
O.
,
1945
, “
The Spacing of Turbomachine Blading, Especially With Large Angular Deflection
,”
Brown Boveri Rev.
,
32
(
12
), pp.
436
444
.
14.
Meingast
,
M.
,
Kielb
,
R. E.
, and
Thomas
,
J. P.
,
2009
, “
Preliminary Flutter Design Method for Supersonic Low Pressure Turbines
,”
ASME
Paper No. GT2009-59177.
15.
Vega
,
A.
, and
Corral
,
R.
,
2013
, “
Physics of Vibrating Airfoils at Low Reduced Frequency
,”
ASME
Paper No. GT2013-94906.
16.
Bölcs
,
A.
, and
Fransson
,
T. H.
,
1986
, “
Aeroelasticity in Turbomachines Comparison of Theoretical and Experimental Cascade Results
,”
Communication du Laboratoire de Thermique Appliquée et de Turbomachines
,
EPFL
, Lausanne, Switzerland, No. 13.
17.
Fransson
,
T. H.
, and
Verdon
,
J. M.
,
1991
, “Updated Report on Standard Configurations for Unsteady Flow Through Vibrating Axial-Flow Turbomachine Cascades,”
KTH
Royal Institute of Technology, Stockholm, Sweden, Technical Report No. 1.
18.
Ekici
,
K.
,
Kielb
,
R. E.
, and
Hall
,
K. C.
,
2010
, “
Forced Response and Analysis of Aerodynamically Asymmetric Cascades
,”
AIAA
Paper No. 2010-6535.
19.
Hall
,
K. C.
,
Thomas
,
J. P.
, and
Clark
,
W. S.
,
2002
, “
Computation of Unsteady Nonlinear Flows in Cascades Using a Harmonic Balance Technique
,”
AIAA J.
,
40
(
5
), pp.
879
886
.
20.
Whitehead
,
D. S.
,
1966
, “
Effect of Mistuning on the Vibration of Turbomachine Blades Induced by Wakes
,”
J. Mech. Eng. Sci.
,
8
(
1
), pp.
15
21
.
21.
Kielb
,
R. E.
,
Hall
,
K. C.
, and
Miyakozawa
,
T.
,
2007
, “
The Effect of Unsteady Aerodynamic Asymmetric Perturbations on Flutter
,”
ASME
Paper No. GT2013-94906.
22.
Crawley
,
E. F.
,
1988
, “
Aeroelastic Formulation for Tuned and Mistuned Rotors
,”
AGARD Manual on Aeroelasticity in Axial-Flow Turbomachines, AGARD-AG-298
, Vol.
2
, pp.
19-1
19-24
.
23.
Shapiro
,
A. H.
,
1953
,
The Dynamics and Thermodynamics of Compressible Fluid Flow
,
The Ronald Press Company
, New York.
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