Gas turbine engines for aircraft and power plants work more efficiently and burn less fuel when they run at temperatures high enough to melt metal.
Hu and Johnson, working behind the university's big wind tunnel, are developing new technologies to accurately test and improve engine cooling strategies. Their current focus is to improve the turbine blades spun by the engine's exhaust. Those blades at the back of the engine drive front blades that force compressed air into the combustion chamber.
"Right now, the current state of the art for engine combustion is about 3,000 degrees Fahrenheit," said Hu, an
One technology is to build hollow turbine blades and blow coolant through an arrangement of holes in the blades. The holes create a cooling film between the hot exhaust gases and the turbine blades, allowing the blades to keep their shape and strength.
But now, as manufacturers experiment with biofuels and efficiency improvements, Hu said combustion temperatures are heading higher and higher. And so it's getting more and more important for engineers to research and develop heat-resistant materials and cooling technologies. Better cooling can mean fuel savings, longer-lasting parts and significant cuts in operating costs.
For the past 19 months, Hu and Johnson, an
Rather than trying to replicate the high temperatures inside a jet engine, the engineers have developed new technologies and room-temperature tests to study the effectiveness of cooling hole shapes, arrangements and the cooling film they create over a turbine blade.
They've built an experimental rig that places a model turbine blade at the bottom of a wind tunnel's test section. Jets of pure nitrogen or carbon dioxide are blown through the model blade's cooling holes. The main stream of the wind tunnel blows oxygen-rich air above the test blade. Using oxygen-sensitive paint on the model blade, an ultraviolet light source and a digital camera, Hu and Johnson can see if the cooling film keeps oxygen molecules from the main stream off the model blade.
"If we find an oxygen molecule on the model blade, we know that the cooling stream didn't create a barrier," Hu said.
So far, the
They've also been using an advanced flow diagnostic technique called particle image velocimetry – seeding the test flows with tiny particles that can be photographed with a laser and camera – to record and measure what happens when gases blow out of the cooling holes.
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