The Central Research Institute of Electric Power Industry (CRIEPI) in Japan recently completed simulations using FLUENT for the heat transfer analysis in a gas turbine. Difficulty in obtaining experimental measurements in gas turbines makes CFD a very attractive tool for establishing standards for gas turbine hot parts life assessment. However, researchers needed to confirm that CFD simulations could provide an accurate analysis before results could be used reliably for actual gas turbine operation and maintenance.

The first stage turbine blade of a 1100°C class gas turbine used by electric power companies in Japan was used in this study. It has multiple-hole-type inner cooling passages. Validation work began by comparing experimental data obtained at the blade mid-span with results from two-dimensional simulations.

Pathlines on the suction side of the blade (left) show a passage vortex at the blade root and tip. On the pressure side (right) a leakage vortex is observed.

Comparisons with measurements of static pressure and Nusselt number at the blade surface showed excellent agreement. Next, a three-dimensional conjugate heat transfer analysis of the complete turbine blade was performed. The RNG k-e turbulence closure and rotating reference frame models were used in this study. On the suction side of the blade, pathlines showed a passage vortex at the blade root and around the blade tip. Also, a leakage vortex was observed at the blade tip. The effects of the leakage vortex on the pressure-side flow field were clearly seen. These predicted flow patterns are in good agreement with the reported qualitative observations. Moreover, the predicted blade surface temperature variations agree very well with the observed surface color pattern.

Rotor blade surface color pattern of the actual gas turbine and simulated temperature contours with FLUENT.

These results give the CRIEPI researchers sufficient confidence to expand their use of CFD for gas turbine thermal analysis. Sensitivity analyses have been carried out with different turbine inlet temperature profiles and cooling air flow rates to investigate the influences of these factors on blade temperature. These results will help CRIEPI researchers to address problems of gas turbine operation and maintenance in the future.

The calculations showed excellent agreement with experimental data.

References:

1. Trans ASME, J. Eng. Gas Turbines & Power (1986). 108, 277-284
2. Trans ASME, J.Turbomachinery (1989). 111, 1-7
3. Trans ASME, J. Eng. Gas Turbines & Power (1985). 107, 1022-1030

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