Research Papers

Investigations of Flutter and Aerodynamic Damping of a Turbine Blade: Experimental Characterization

[+] Author and Article Information
Charles E. Seeley

GE Global Research
Niskayuna, NY 12309
e-mail: seeley@ge.com

Christian Wakelam

GE Global Research
Munich 85748, Germany
e-mail: christian.wakelam@ge.com

Xuefeng Zhang

GE Global Research
Niskayuna, NY 12309
e-mail: xue.zhang@ge.com

Douglas Hofer

GE Global Research
Niskayuna, NY 12309
e-mail: douglas.hofer@ge.com

Wei-Min Ren

GE Global Research
Niskayuna, NY 12309
e-mail: weimin.ren@ge.com

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received October 6, 2016; final manuscript received January 6, 2017; published online April 4, 2017. Editor: Kenneth Hall.

J. Turbomach 139(8), 081011 (Apr 04, 2017) (7 pages) Paper No: TURBO-16-1273; doi: 10.1115/1.4035840 History: Received October 06, 2016; Revised January 06, 2017

Flutter is a self-excited and self-sustained aero-elastic instability, caused by the positive feedback between structural vibration and aerodynamic forces. A two-passage linear turbine cascade was designed, built, and tested to better understand the phenomena and collect data to validate numerical models. The cascade featured a center airfoil that had its pitch axis as a degree-of-freedom to enable coupling between the air flow and mechanical response in a controlled manner. The airfoil was designed to be excited about its pitch axis using an electromagnetic actuation system over a range of frequencies and amplitudes. The excitation force was measured with load cells, and the airfoil motion was measured with accelerometers. Extraordinary effort was taken to minimize the mechanical damping so that the damping effects of the airflow over the airfoil, that were of primary interest, would be observable. Assembling the cascade required specialized alignment procedures due to the tight clearances and large motion. The aerodynamic damping effects were determined by observing changes in the mechanical frequency response of the system. Detailed aerodynamic and mechanical measurements were conducted within a wide range of Mach numbers (Ma) from Ma = 0.10 to 1.20. Experimental results indicated that the aerodynamic damping increased from Ma = 0.10 to 0.65, dropped suddenly, and was then constant from Ma = 0.80 to 1.20. A flutter condition was identified in the interval between Ma = 0.65 and Ma = 0.80. The aerodynamic damping was also found to be independent of displacement amplitude within the tested range, giving credence to linear numerical approaches.

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Fig. 1

Flutter rig overview. Airflow is right to left in this cut view.

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Fig. 2

Actuation system enables the controlled mechanical excitation of the airfoil about its pitch axis

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Fig. 3

Flutter rig close-up showing coil and load cell as part of the actuation system

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Fig. 4

Stationary instrumentation in SS insert

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Fig. 5

Instrumentation, controls, and data acquisition

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Fig. 6

Damping determined from airfoil frequency response

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Fig. 7

Actuation system on bench top for shakedown. Patches of reflective tape show measurement points by laser vibrometer.

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Fig. 8

Measured airfoil mode shape was purely rigid body torsional as required as indicated by displacement contours

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Fig. 9

Analytical fit to experimental frequency response function

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Fig. 10

Damping with air OFF (mechanical damping only, no aerodynamic damping) nearly constant over a range of displacement amplitude

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Fig. 11

Aerodynamic damping nearly constant over a range of displacement amplitude for 0.10 < Ma < 0.51. Ma = 0.65 is an exception because it is near the flutter condition at Ma = 0.70.

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Fig. 12

Aerodynamic damping nearly constant over a range of displacement amplitude for 0.80 < Ma < 1.20

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Fig. 13

Aerodynamic work as a function of Mach number




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