As demand grows for increased gas turbine efficiency, engine manufacturers are challenged with creating designs that operate at higher temperatures. But that becomes a significant challenge as temperatures approach the melting point of some engine component material. A well-established method for maintaining turbine blade temperatures at acceptable levels is to employ “film-cooling,” a technique in which cooler, compressor-discharge air is detoured around the combustor then ejected from precisely-machined holes placed over the surface of the turbine airfoil. Excessive use of compressor air for turbine film cooling can, however, reduce engine efficiency.
Historically, film-cooling-hole-placement on turbine airfoils has been optimised by elaborate experiments, sometimes necessitating engine testing. For decades, research engineers have been developing computer simulations of film cooling geometries with the ambition of reducing – if not eliminating – the need for expensive, time-consuming rig testing.
Stanford, with support from Honeywell and ANSYS, is performing a new type of testing with 3-D magnetic resonance velocimetry to measure the velocity and concentration field in a test section. These methods measure the turbulent interaction of crossflow jets with the main flow, for a variety of jet configurations and orientations. These data sets provide an important benchmark against which the large available range of ANSYS turbulence models and computational methods can be compared. The objective is to develop validated models, methods and best practices for prediction of film cooling.
“This is the first time that an engineering software company has supported an extensive test series like this, and it illustrates the commitment of ANSYS to the continued upgrade of the turbulence models in ANSYS computational fluid dynamics solutions,” said John K. Eaton, the Charles Lee Powell Foundation professor in Stanford’s School of Engineering. “Our combined efforts are aimed at validating the turbulent mixing models in these tools over entire complex flow fields, something that has never been done before. Conducting this testing over a wide range of film cooling conditions provides a comprehensive test of the predictive capability.”
“At 30,000 feet in the air, there’s little margin for error,” said Brad Hutchinson, global industry director for industrial equipment and rotating machinery at ANSYS. “By always focusing on solving the most complex problems – like the thin film cooling challenge Honeywell and Stanford are addressing – ANSYS ensures that our customers are armed with the tools that will help them to create new products.”