Conjugate Heat Transfer Approach to Gas Turbine Engine Modeling

Abstract There is an increasing pressure on the aviation industry to rein in its emissions in light of the global climate change. The sector is ripe for introducing innovations to power the next generation of aircrafts. The hot-gas-path components in gas turbine engines remain a key area for further innovations to drive up efficiency. Since the total work derived from the turbine is a function of the turbine entry temperature (TET), the past few decades have seen a steady growth in TETs. This has been possible by the use of single crystal blades, thermal barrier coatings (TBC) and improved cooling mechanisms. The present form of turbine blades is the result of decades of constant innovation. Modeling the flow of heat through this multi-material, multi-layered feat of engineering has usually been restricted to conductive and convective mode of heat transfer. However, with rising TETs, the fraction of heat transferred via radiation will increase exponentially. The present study is the result of an effort to develop a comprehensive conjugate heat transfer model incorporating the effects of conductive, convective, and radiative heat transfer. Thermal radiation, which has been largely ignored in past conjugate heat transfer approaches, will be a key element in the design of future turbine blades and other hot-gas-path components. The model evaluated the variation in thermal barrier coating thickness, conductivities, effectiveness of internal cooling mechanisms, etc., to build a robust map of the temperature distribution across the turbine blade at TETs as high as 2300 K. Results showed that the inclusion of radiation in the model has a large impact on the temperature distribution within the blade. The effects vary from the dominance of radiative heat transfer to the blade at elevated temperatures to radiative cooling from the emissive blade surface at lower operating temperatures. Moreover, the findings indicate the inability of current convective and conductive cooling mechanisms to counter higher TETs. Therefore, novel low-conductivity coatings and cooling mechanisms were modeled and have been found to outperform the state-of-the-art by as much as 200 K, for a comparable value of thickness. Therefore, approaches combining conduction, convection and radiation must be used to develop the next generation of blades, leading to more efficient, reliable and environment-friendly gas turbines.