Abstract

This paper describes the identification and prediction of a new class of nonsynchronous vibration (NSV) problem encountered during the development of an advanced design composite fan stator for an aircraft engine application. Variable exhaust nozzle testing on an instrumented engine is used to map out the NSV boundary, with both choke- and stall-side instability zones present that converge toward the nominal fan operating line and place a limit on the high-speed operating range. Time-accurate three-dimensional viscous CFD analyses are used to demonstrate that the NSV instability is being driven by dynamic stalling of the fan stator due to unsteady shock-boundary layer interaction. The effects of downstream struts in the front frame of the engine are found to exasperate the problem, with the two fat service struts in the bypass duct generating significant spatial variations in the stator flow field. Strain gage measurements indicate that the stator vanes experiencing the highest vibratory strains correspond to the low static pressure regions of the fan stator assembly located approximately 90 degrees away from the two fat struts. The CFD analyses confirm the low static pressure sectors of the stator assembly are the passages in which the flow-induced NSV instability is initiated due to localized choking phenomena. The CFD predictions of the instability frequency are in reasonable agreement with the strain gage data, with the strain gage data indicating that the NSV response occurs at a frequency approximately 25% below the frequency of the fundamental bending mode. The flow patterns predicted by the CFD analyses are also correlated with the results of an engine flow visualization test to demonstrate the complex nature of the flow field.

Issue Section:
Technical Papers
Keywords:
vibrations, confined flow, boundary layers, flow instability, nozzles, stators, flow visualisation, computational fluid dynamics, aerodynamics, pipe flow, aerospace engines
Topics:
Flow (Dynamics), Pressure, Stators, Vibration, Computational fluid dynamics, Composite materials, Strain gages, Engines
1.
Schlichting, H., 1987, Boundary-Layer Theory, Seventh Edition, McGraw-Hill, New York, Chap. 2.
2.
Skop
,
R. A.
, and
Griffin
,
O. M.
,
1973
, “
A Model for the Vortex-Excited Resonant Response of Bluff Cylinders
,”
J. Sound Vib.
,
27
(
2
), pp.
225
–
233
.
3.
Blevins
,
R. D.
, and
Burton
,
T. E.
,
1976
, “
Fluid Forces Induced by Vortex Shedding
,”
ASME J. Fluids Eng.
,
98
(
2
), pp.
19
–
26
.
4.
Zaman
,
K. B. M. Q.
,
McKinzie
,
D. J.
, and
Rumsey
,
C. L.
,
1989
, “
A Natural Low-Frequency Oscillation of the Flow Over an Airfoil Near Stalling Conditions
,”
J. Fluid Mech.
,
202
, pp.
403
–
442
.
5.
Rumsey, C. L., Thomas, J. L., Warren, G. P., and Liu, G. C., 1986, “Upwind Navier-Stokes Solutions for Separated Periodic Flows,” AIAA Paper No. 86-0247.
6.
Rumsey, C. L., 1987, “A Computational Analysis of Flow Separation Over Five Different Airfoil Geometries at High Angles-of-Attack,” AIAA Paper No. 87-0188.
7.
Camp
,
T. R.
,
1999
, “
A Study of Acoustic Resonance in a Low-Speed Multistage Compressor
,”
ASME J. Turbomach.
,
121
(
1
), pp.
36
–
43
.
8.
Mailach, R., Sauer, H., and Vogeler, K., 2001, “The Periodical Interaction of the Tip Clearance Flow in the Blade Rows of Axial Compressors,” ASME Paper No. 2001-GT-0299.
9.
Lenglin, G., and Tan, C. S., 2002, “Characteristics of Wake- and Tip-Vortex-Induced Unsteady Blade Response in Multistage Compressor Environment,” 7th National Turbine Engine High Cycle Fatigue (HCF) Conference, W. Palm Beach, FL, May 2002.
10.
Kielb, R. E., Thomas, J. P., Barter, J. W., and Hall, K. C., 2003, “Blade Excitation by Aerodynamic Instabilities – A Compressor Blade Study,” ASME Paper No. GT2003-38634.
11.
Shabbir, A., and Zhu, J., 1996, “Assessment of Three Turbulence Models in a Compressor Rotor,” ASME Paper No. 96-GT-198.
12.
Sanders
,
A. J.
,
Hassan
,
K. K.
, and
Rabe
,
D. C.
,
2004
, “
An Experimental and Numerical Study of Stall Flutter in a Transonic Low-Aspect Ratio Fan Blisk
,”
ASME J. Turbomach
126
(
1
), pp.
166
–
174
.
13.
Bakhle, M. A., Srivastava, R., and Keith, Jr., T. G., 1997, “A 3D Euler/Navier-Stokes Aeroelastic Code for Propulsion Applications,” AIAA Paper No. 97-2749.
14.
Bakhle, M. A., Srivastava, R., and Keith Jr., T. G., 1998, “Aeroelastic Calculations Based on Three-Dimensional Euler Analysis,” AIAA Paper No. 98-3295.
15.
Chen, J. P., and Whitfield, D. L., 1993, “Navier-Stokes Calculations for the Unsteady Flowfield of Turbomachinery,” AIAA Paper No. 93-0676.
16.
Srivastava, R., Bakhle, M. A., and Keith, Jr., T. G., 1999, “Phase-Lagged Boundary Condition Methods for Aeroelastic Analysis of Turbomachines—A Comparative Study,” ASME Paper No. 99-GT-19.
17.
Hall, E. J., and Delaney, R. A., 1995, Investigation of Advanced Counterrotation Blade Configuration Concepts for High Speed Turboprop Systems: Task VII—ADPAC Users Manual, NASA CR 195472.
18.
Cumpsty, N. A., 1989, Compressor Aerodynamics, Longman Group, UK, Chap. 9.
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