A grant from the Air Force Office of Science Research will help researchers improve the design of jet engine turbine blades.
The collaborative project takes advantage of a unique resource at the Department of Energy’s Idaho National Engineering and Environmental Laboratory. University of Idaho researchers will use the INEEL’s Matched Index of Refraction Flow System (MIR) to investigate how air flows around the blades. The INEEL facility is the largest MIR system in the world.
The researchers plan to study disturbances in flow around a quartz model that simulates a turbine blade’s surface. But instead of relying on a supercomputer or wind tunnel to study flow, they will use baby oil and lasers.
The MIR facility takes advantage of a simple light trick. Keeping the oil at 86 degrees means that light, such as a laser beam, passes through the baby oil and the quartz with the same resistance. For example, light traveling through air angles its path upon entering water. That’s why objects underneath water appear distorted and offset. But light passes through the oil-quartz boundary without distortion, permitting the researchers to view flow around (and inside) complicated structures.
Lasers allow the researchers to measure fluid flow very close to a model’s surface. “The laser light reflects off dust particles in the oil,” explains INEEL researcher Don McEligot, a technical leader in Experimental Thermal Science. In wind tunnels, sensors attached to an object measure changes in fluid flow and often interfere with those measurements. But at the MIR facility, computer-controlled sensors outside the oil chamber pick up laser light reflections, and a computer recreates the flow pattern.
The goal is to model “realistic roughness.” Turbine blades twirl behind the combustion chamber in a jet engine, converting the superheated, super-fast exhaust into propulsion. Over time, the blades lose their original smooth surface due to normal wear and tear. “They get deposits on them and cracks will form, eventually making a surface that looks like the surface of a golf ball,” says Ralph Budwig, chair of the Department of Mechanical Engineering at the University of Idaho in Moscow. Perturbations in air flowing around the blades can decrease an engine’s performance, and the pits and divots of realistic roughness produce such disturbances.
“It’s difficult to characterize realistic roughness with mathematical equations,” says Budwig, who specializes in developing techniques to measure velocity, temperature, and other conditions in fluid flows. Unlike the regular hills and valleys of a piece of sandpaper, the roughness on a turbine blade is random. Realistic roughness is as difficult to predict as random systems like the weather.
The MIR facility will allow University of Idaho doctoral student Hugh McIlroy to make detailed measurements of how roughness creates variations in flow. “The results of the research will improve performance and reduce maintenance costs,” says McIlroy. This includes ways to determine the best time to replace the blades.
The team will also examine the blade’s heat transfer properties. The air streaming out of a jet engine’s combustion chamber is hotter than the blade’s melting temperature, so turbine blades must be cooled internally. Understanding how the surface roughness affects the blade’s ability to resist these high-temperature gases is a step towards improved performance. “We’re among the first to use fluid flow to understand the effects of realistic roughness,” says UI's Budwig.
The grant is part of a Department of Defense program to encourage competitive research in less-populated states. Currently, 17 states are eligible for the program, known as the Department of Defense Experimental Program to Stimulate Competitive Research, or DEPSCoR. Budwig will receive approximately $315,000 over three years, part of which funds Mackelroy’s dissertation research.
The INEEL is a science-based, applied engineering national laboratory dedicated to supporting the U.S. Department of Energy's missions in environment, energy, science and national defense. The INEEL is operated for the DOE by Bechtel BWXT Idaho, LLC, in partnership with the Inland Northwest Research Alliance.
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Editor’s note: For more information on the DEPSCoR programs, visit http://www.aro.army.mil/research/dep01baa.htm
For more information on the Matched Index of Refraction facility, visit http://inelext1.inel.gov/science/feature.nsf/ineel/mir.
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