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Research Papers

Predictions of Unsteady Interactions Between Closely Coupled High Pressure- and Low Pressure-Turbines With Co- and Counterrotation

[+] Author and Article Information
R. E. Gacek

United Technologies, Pratt & Whitney,
East Hartford, CT 06108

Contributed by the International Gas Turbine Institute (IGTI) Division of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received March 21, 2011; final manuscript received January 31, 2013; published online September 13, 2013. Editor: David Wisler.

J. Turbomach 135(6), 061008 (Sep 13, 2013) (9 pages) Paper No: TURBO-11-1048; doi: 10.1115/1.4024635 History: Received March 21, 2011; Revised January 31, 2013

Here, we report on an analytical study of the unsteady aerodynamic interactions of a closely coupled, corotating, high- and low-pressure turbine configuration. The effort was focused on the prediction of unsteady surface pressures imparted on the first blade of the low-pressure turbine (LPT). As a first step, a baseline three-row time-accurate prediction was carried out for the first three rows of the low-pressure turbine (vane-blade-vane). In contrast to the three-row results, a four-row analysis, which included the blade of the high-pressure turbine, revealed that the temporally varying tangential load on the LPT blade was increased in amplitude by a factor of five compared to the three-row case with a shift in primary unsteady energy to unexpected frequencies. In the four-row analysis, a region of unusually high unsteadiness near the tip of the LPT blade was also characterized by an increase in the amplitude of the fluctuating surface pressure by a factor of nearly seven, again, with unexpected attendant frequencies. A model is presented which explains the unexpected frequencies realized in the four-row results and allows the predetermination of these frequencies without the use of computational fluid dynamics. In an effort to better understand the complex interactions between the high- and low-pressure turbines, the first vane of the low-pressure turbine was redesigned, and the remaining airfoils were reoriented, to establish a counterrotating turbine configuration. While substantial reductions in unsteady surface-pressure amplitudes were realized near the tip of the LPT blade with the switch to counterrotation, the amplitude of the temporally varying tangential load on the blade remained notably higher than that from the three-row analysis. The precise physical cause for the high levels of local unsteadiness near the tip of the first LPT blade in the corotating configuration remains unclear.

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References

Figures

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Fig. 1

Cross-sectional schematic of HPT and LPT configurations considered for this study (V: vane, B: blade)

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Fig. 2

Comparison of instantaneous tangential loads on the first LPT blade from the 3- and 4-row time-accurate simulations of the corotating configuration

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Fig. 3

Discrete fourier transform results for the instantaneous tangential load information shown in Fig. 2

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Fig. 4

Time-mean and unsteady surface-pressure loadings on the LPT blade from 3- and 4-row simulations at select span-wise locations

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Fig. 5

Model of interactions between the HPT and LPT airfoils illustrating parceled HPT blade-wake trains entering the LPT blade. Airfoils are not to scale.

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Fig. 6

Illustration of reference frame change which enables the calculation of pertinent frequencies which dominate the unsteady interactions. Airfoils are not to scale.

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Fig. 7

Comparisons of distributions of RMS surface pressures on the suction side of the LPT first blade from 3- and 4-row simulations. Also shown are detailed time traces and DFT results from regions of high (relative to each configuration) unsteadiness.

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Fig. 8

Time-mean total pressure and axial momentum at the exit of the LPT first vane for 3- and 4-row simulations

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Fig. 9

Overview of conversion from a corotation configuration to a counterrotating one. Airfoils are not to scale.

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Fig. 10

Time-mean and unsteady surface-pressure loadings on the LPT blade from co- and counterrotating configurations (both 4 row) at select spanwise locations

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Fig. 11

Time-mean total pressure and axial momentum at the exit of the LPT first vane for co- and counterrotating 4-row simulations

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Fig. 12

Comparisons of distributions of RMS surface pressures on the suction side of the LPT first blade from co- and counterrotating turbine configurations (both 4-row simulations). Also shown are detailed time traces and DFT results from regions of high (relative to each configuration) unsteadiness.

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Fig. 13

Comparison of temporal history of instantaneous tangential loads on the LPT blade from 3- and 4-row corotating simulations, as well as the counterrotating 4-row results

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