Gas-Turbine Heat Transfer – Issues and Challenges
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Wednesday, December 3, 2014 - 11:30am to 1:00pm
Professor Tom I-P. Shih
The efficiency and service life of a gas-turbine engine is strongly affected by its turbine component, where the thermal energy contained in the high-pressure and high-temperature gas is converted into mechanical energy. The most effective way to improve the efficiency of the turbine component is to raise the temperature of the gas that enters it, which could be as high as the adiabatic flame temperature from the combustion of fuel and oxidizer. Advances in two areas have enabled the steady increase in the turbine inlet temperature over the past few decades. One is the development of high-temperature-resistant materials, and the other is the development of innovative cooling technologies. With cooling, the material’s temperature can be maintained below the maximum allowable even though the temperature of the gas in the turbine’s hot-gas path far exceeds it. Since cooling requires work, efficiency demands effective cooling with the minimum amount of cooling flow.
Considerable efforts have been made for decades to quantify heat transfer for a wide variety of geometries and to develop efficient and effective cooling designs. With these and other efforts, great progress has been made as evidenced by the impressive advances in the efficiency and the service life of gas turbines over the years. Every advance has required a significant leap in understanding and insight. Computational fluid dynamics and heat transfer (CFD/HT) offers the potential to provide the leap in understanding and insight that are needed to make the next advance in cooling. However, there are issues that affect the reliability of CFD/HT in predicting the flow and the heat transfer with the accuracy that is needed to make the next advance. This is because CFD/HT, like any tool, whether mathematical or experimental, has inherent sources of errors.
This talk gives an overview of turbine cooling and addresses some issues and challenges that affect the reliability of CFD/HT in the design and analysis of turbine-cooling strategies. In particular, examples are given on validation of CFD/HT to illustrate capabilities and limitations of well-known turbulence models via steady & unsteady RANS and to show problems where LES is needed. Since the integrity of the validation process depends on the integrity of the experimental data, uncertainties associated with steady and unsteady measurements of the heat transfer are discussed and some solutions proposed. Results are also presented to show the challenges of cooling turbine material when heating loads increase suddenly and the effects of averaging the heat-transfer coefficient from CFD/HT or experimental measurements on the predicted cooling requirement.
Tom Shih is Professor and Head of the School of Aeronautics and Astronautics at Purdue University. Previously, he was a faculty member at Iowa State University (2003-09), Michigan State University (1998-2003), Carnegie Mellon University (1988-98), and the University of Florida (1983-88). He started his undergraduate education at West Virginia University, but completed his BS degree at the National Cheng Kung University in Taiwan. His MS and PhD degrees are from The University of Michigan in Ann Arbor. He is a Fellow of ASME and AIAA. His research interests are in CFD/HT, turbine cooling, aircraft icing, and control of shock-wave/boundary-layer interactions.