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Research Papers

Experimentally Verified Study of Regeneration-Induced Forced Response in Axial Turbines

[+] Author and Article Information
Jens Aschenbruck

Institute of Turbomachinery and Fluid Dynamics,
Leibniz Universitaet Hannover,
Appelstr. 9,
Hannover 30167, Germany
e-mail: aschenbruck@tfd.uni-hannover.de

Joerg R. Seume

Professor
Senior Mem. ASME
Institute of Turbomachinery and Fluid Dynamics,
Leibniz Universitaet Hannover,
Appelstr. 9,
Hannover 30167, Germany
e-mail: seume@tfd.uni-hannover.de

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 25, 2014; final manuscript received August 1, 2014; published online September 30, 2014. Editor: Ronald Bunker.

J. Turbomach 137(3), 031006 (Sep 30, 2014) (10 pages) Paper No: TURBO-14-1177; doi: 10.1115/1.4028350 History: Received July 25, 2014; Revised August 01, 2014

Geometrical variations occur in highly loaded turbine blades due to operation and regeneration. To determine the influence of such regeneration-induced variances of turbine blades on the aerodynamic excitation, a typical stagger angle variation of overhauled turbine blades is applied to stator vanes of an air turbine. This varied turbine stage is numerically and experimentally investigated. For the aerodynamic investigation of the vane wake, computational fluid dynamics (CFD) simulations are conducted. It is shown that the wake is changed due to the stagger angle variation. These results are confirmed by aerodynamic probe measurements in the air turbine. The vibration amplitude of the downstream rotor blades has been determined by a computational forced response analysis using a unidirectional fluid–structure interaction (FSI) approach and is experimentally verified here by tip-timing measurements. The results of the simulations and the measurements both show significantly higher amplitudes at certain operating points (OPs) due to the additional wake excitation. For typical regeneration-induced variations in stagger angle, the vibration amplitude is up to five times higher than in the reference case of uniform upstream stators. Based upon the present results, the influence of these variations and of the vane patterns on the vibration amplitude of the downstream rotor blade can and should be estimated in the regeneration process to minimize the dynamic stresses of the blades.

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References

Figures

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Fig. 1

Five-stage air turbine

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Fig. 2

Campbell diagram and EFs of the rotor blade stage five

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Fig. 3

Five-hole pneumatic probe

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Fig. 9

Comparison of the wakes at OP2 of the reference and the alternating vane at midspan

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Fig. 8

Velocity downstream of the last turbine stage at OP2

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Fig. 7

Relative total pressure downstream of the last turbine stage at OP2

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Fig. 6

Computational mesh of the fifth stage at midspan

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Fig. 5

Position of the tip-timing probes (perspective: upstream)

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Fig. 4

Tip-timing probes installed in the axial air turbine

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Fig. 10

Integrated pressure on the blade from unsteady CFD in time domain and the frequency domain

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Fig. 11

Flow chart of the unidirectional FSI approach using the harmonic response analysis [15]

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Fig. 12

Numerically determined blade vibration amplitudes for two configurations

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Fig. 15

Low scatter of the blade resonance frequencies at OP2

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Fig. 16

Blade vibration amplitude for reference and alternating configuration at OP2

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Fig. 17

Blade vibration amplitude for reference and alternating configuration at OP3

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Fig. 18

Comparison of the simulated and measured blade vibration amplitudes for different OPs

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Fig. 13

Blade vibration amplitude for reference and alternating configuration at OP1

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Fig. 14

High scatter of the blade resonance frequencies at OP1

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Fig. 19

Sensitivity of the vibration amplitude depending on the damping ratio and comparison to the experimental results

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