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Research Papers

Investigation of Turbine Shroud Distortions on the Aerodynamics of a One and One-Half Stage High-Pressure Turbine

[+] Author and Article Information
Eric A. Crosh, Charles W. Haldeman, Michael G. Dunn

Gas Turbine Laboratory, Ohio State University, 2300 West Case Rd., Columbus, OH 43235

D. Graham Holmes, Brian E. Mitchell

 GE Global Research Center, One research Circle, Niskayuna, NY 12309

J. Turbomach 133(3), 031002 (Nov 11, 2010) (12 pages) doi:10.1115/1.4001176 History: Received July 22, 2009; Revised July 26, 2009; Published November 11, 2010; Online November 11, 2010

As part of a proactive effort to investigate the ability of computational fluid dynamics tools to predict time-accurate surface-pressure histories, a combined experimental/computational investigation was performed, examining the effect of rotor shroud (casing) out-of-roundness on the unsteady pressure loading for the blade row of a full-stage turbine. The casing out-of-roundness was idealized by designing a casing ring with a sinusoidal variation. This casing ring was used to replace a flat casing for an existing turbine, and direct comparisons were made between the time-accurate pressure measurements and predictions obtained using the flat and “wavy” casings. For both casing configurations, predictions of the unsteady pressure loading for many locations on the blade and vane were obtained using Numeca’s FINE/TURBO code and General Electric’s turbine and compressor analysis (TACOMA) code. This paper will concentrate on the results obtained for the wavy casing, but the results for the flat casing are presented as a baseline case. The time-accurate surface-pressure measurements were acquired for the vane and blade of a modern, 3D, 1 and 1/2 stage high-pressure turbine operating at the design corrected speed and stage pressure ratio. The research program utilized an uncooled turbine stage for which all three airfoil rows are heavily instrumented at multiple spans to develop a full data set. The vane-blade-vane count for this machine is 38-72-38. The number of waves in the distorted shroud “wavy wall” is approximately 1.5 times the number of vanes. The resulting changes in the aerodynamic surface-pressure measurements were measurable at all blade spanwise locations. Variations in the time-averaged surface pressure of up to 5% of the flat casing values were observed. In addition, the frequency content of the time-resolved blade data for the wavy casing changed substantially from that measured using the flat casing, with changes in both amplitudes and frequencies. Imposing the casing irregularity changed the fundamental physics of the problem from a single frequency and its harmonics to a multifrequency problem with mixed harmonics. The unsteady effects of this type of problem can be addressed using the harmonic method within Numeca’s FINE/TURBO code, which is designed to handle multiple blade passing frequencies and harmonics for one blade row. A more traditional approach is included in this paper by employing the TACOMA code in a linearized mode that produces results for a single frequency. These results show that casing irregularity can have a significant influence on the blade surface-pressure characteristics. Further, it is demonstrated that the FINE/TURBO code experienced difficulty in predicting the unsteady pressure signal attributed to the wavy casing configuration, while at the same time, in capturing the unsteady signal attributed to the vane passing due to limitations in the current methodology.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Flow path from the upstream to the downstream rakes

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Figure 2

Photograph of the wavy casing

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Figure 3

Visualization of the solid boundaries showing the O- and H-blocks

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Figure 4

Static pressure fluctuation for the flat casing on the blade at 50% span and 10% wetted distance (suction surface)

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Figure 5

Static pressure fluctuation for the flat casing on the blade at 50% span and −20% wetted distance (pressure surface)

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Figure 6

HPV time-averaged data and predictions: 15%, 50%, and 90% spans

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Figure 7

HPB time-averaged data and predictions: 15%, 50%, and 90% spans

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Figure 8

Normalized pressure for the HPB at 90% span and −40% wetted distance on the pressure surface

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Figure 9

FFT for the HPB at 90% span and −40% wetted distance

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Figure 10

Normalized surface pressure for HPB at 15% span and 10% wetted distance on the suction surface

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Figure 11

FFT for HPB at 15% span and 10% wetted distance on the suction surface

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Figure 12

Normalized surface pressure on HPB at 50% span and 10% wetted distance on the suction surface

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Figure 13

FFT for HPB at 50% span and 10% wetted distance on the suction surface

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Figure 14

HPB 90% span at 20% wetted distance flat and wavy casing data

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Figure 15

FFT of HPB pressure data for 15% span at 30% wetted distance on suction surface for flat and wavy casings

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Figure 16

HPB 90% span TACOMA predictions and experimental data for the wavy casing at the fundamental shroud sine wave passing frequency

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Figure 17

Normalized pressure envelope amplitude at 15%, 50%, and 90% spans on the high-pressure blade

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Figure 18

Amplitude of the normalized pressure at 15%, 50%, and 90% spans on the high-pressure blade at the fundamental vane passing frequency

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Figure 19

Amplitude of the normalized pressure at 15%, 50%, and 90% spans on the high-pressure blade at the fundamental wave passing frequency

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