Aerospace Engineering Seminar
Gas turbines, a trillion-dollar industry, are widely used for propulsion and electric-power generation. Though tremendous advances have been made since its invention in the 1930's with Frank Whittle's and Hans von Ohain's patents, there are still huge opportunities for further advances in efficiency. One of the most effective ways to improve efficiency that has been exploited for decades and still available today is to enable higher gas temperatures to enter its turbine component, which could be as high as the adiabatic flame temperature from the combustion of fuel and air in the combustor. Though the turbine's inlet temperatures have steadily increased over the years, they are still below the maximum possible and hence the opportunity. The challenge is that the current inlet temperatures already far exceed, by hundreds of degrees Celsius, the maximum temperature at which even the best turbine materials (e.g., Ni-based super alloys) lose strength and durability. Currently, 15 to 30% of the air entering the compressor are used to cool materials that come in contact with the hot gases in the turbine component – air that could be used to generate thrust or power. Thus, reducing the amount of cooling flow needed is another opportunity to improve efficiency. To further increase the turbine's inlet temperature or reduce the cooling flow needed will require a leap beyond existing materials as well as our understanding of cooling science and engineering. This talk provides an overview on turbine cooling and some of the challenges and opportunities that could enable a leap forward. Some questions to be discussed include: How universal is Newton's law of cooling in quantifying heat transfer in extreme environments? How does one define or measure the bulk temperature in complicated configurations? Could transient methods be used to measure the heat-transfer coefficient in complicated configurations as is commonly done? How does one scale measurements made under laboratory condition to engine conditions? What are the uncertainties on verification and validation for RANS and LES simulations of turbine cooling?