Research Papers

A Thermodynamic Model to Quantify the Impact of Cooling Improvements on Gas Turbine Efficiency

[+] Author and Article Information
Selcuk Can Uysal, Eric Liese

National Energy Technology Laboratories,
Morgantown, WV 26505

Andrew C. Nix

Mechanical and Aerospace Engineering Department,
West Virginia University,
Morgantown, WV 26505

James Black

National Energy Technology Laboratories,
Pittsburgh, PA 15236

1This work was done under the U.S. Department of Energy (DoE) Graduate Research Program at the National Energy Technology Laboratory (NETL), managed by the Oak Ridge Institute for Science and Education (ORISE). Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received November 14, 2017; final manuscript received November 20, 2017; published online December 20, 2017. Editor: Kenneth Hall.

J. Turbomach 140(3), 031007 (Dec 20, 2017) (11 pages) Paper No: TURBO-17-1213; doi: 10.1115/1.4038614 History: Received November 14, 2017; Revised November 20, 2017

Cooling of turbine hot-gas-path components can increase engine efficiency, reduce emissions, and extend engine life. As cooling technologies evolved, numerous blade cooling geometries have been and continue to be proposed by researchers and engine builders for internal and external blade and vane cooling. However, the impact of these improved cooling configurations on overall engine performance is the ultimate metric. There is no assurance that obtaining higher cooling performance for an individual cooling technique will result in better turbine performance because of the introduction of additional second law losses, e.g., exergy loss from blade heat transfer, cooling air friction losses, and fluid mixing, and thus, the higher cooling performance might not always be the best solution to improve efficiency. To quantify the effect of different internal and external blade cooling techniques and their combinations on engine performance, a cooled engine model has been developed for industrial gas turbines and aero-engines using MATLAB Simulink. The model has the flexibility to be used for both engine types and consists of uncooled on-design, turbomachinery design, and a cooled off-design analysis in order to evaluate the engine performance parameters by using operating conditions, polytropic efficiencies, material information, and cooling system information. The cooling analysis algorithm involves a second law analysis to calculate losses from the cooling technique applied. The effects of variations in engine parameters such as turbine inlet temperature, by-pass ratio, and operating temperature are studied. The impact of variations in metal Biot number, thermal barrier coating (TBC) Biot number, film cooling effectiveness, internal cooling effectiveness, and maximum allowable blade temperature on engine performance parameters are analyzed. Possible design recommendations based on these variations, and direction of use of this tool for new cooling design validation, are presented.

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Fig. 1

Cooled turbine stage components used in the model shown with hot and cold side gas flows

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Fig. 2

Schematic of the model for entropy generation calculations

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Fig. 3

The heat transfer model used in this study shown with associated entropy terms for a blade having internal and external cooling (film cooling) with a TBC layer

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Fig. 4

Cooling analysis model flowchart including the submodels

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Fig. 5

Stator entropy rise calculated for each source term and compared with results from Young and Wilcock [7]

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Fig. 6

Flowchart for the cooled engine models

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Fig. 7

Flowchart of the cooled off-design section

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Fig. 8

The effect of changing engine by-pass ratio is compared for thrust and thrust-specific fuel consumption

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Fig. 9

The effect of changing the turbine inlet temperature is compared for thrust and propulsive efficiency

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Fig. 10

The effect of changing the turbine inlet temperature is compared for thermal efficiency and power-specific fuel consumption

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Fig. 11

The effect of changing the ambient temperature is compared for shaft power delivered and thermal efficiency

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Fig. 12

Sensitivity of thermal efficiency of engine on selected cooling parameters

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Fig. 13

Sensitivity of shaft power delivered on selected cooling parameters

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Fig. 14

Sensitivity of total coolant flowrates on selected cooling parameters



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