Examples of Success
The successes in the AGTSR program are too numerous to re-count. The following examples are offered to exemplify the work car-ried out in the three program areas.
Combustion
Instability Control for Low Emissions Combustors—Georgia Tech. Gas turbine design today in-corporates lean pre-mix combustion to reduce NO emissions. Effective
x
mixing of the high volume of air with the fuel for lean combustion is dif-ficult and often leads to combustion instability that can cause vibration and damage, or turbine shutdown. Georgia Tech developed an auto-matic means to actively detect the onset of combustion instabilities, identify combustion characteristics, and “instantaneously” attenuate the unstable mode. Georgia Tech first fabricated a low-NOx gas turbine simulator to develop the Active Con-trol System. Siemens Westinghouse carried out successful verification testing on a full-scale 3-MW gas turbine combustor. The observed four-fold reduction in amplitudes of combustion pressure oscillations represents a major milestone in the implementation of active combus-tion control. Two patents have been issued on the Georgia Tech technol-ogy, a third is pending, and the tech-nology is being transferred to industry. NASA has purchased an Active Control System for testing.
Computer Code Improve-ments for Low Emission Combus-tor Design—Cornell University. It is crucial for low emission turbine combustor design codes to accu-rately predict NOx and CO emis-sions. To date, computer codes used
Active Control System identifies combustion instabilities and instantaneously
attenuates the unstable mode
for combustor emission design have either impractically long run times, or have unacceptable computational inaccuracies. Cornell University has improved significantly upon an in situ adaptive tabulation (ISAT) al-gorithm, which reduces computer computation times for combustion chemistry by a factor of 40. In con-trolled piloted jet flame validation tests, the improved ISAT accurately predicted NOx and CO levels, as well as local extinction and re-ignition. At least one gas turbine manufac-turer has already incorporated the improved ISAT algorithm into their combustor design system.
Aerodynamics and Heat Transfer
Advanced Component Cool-ing for Improved Turbine Perfor-mance—Clemson University. Materials and air cooling tech-niques—used in the past to enable high turbine inlet temperatures and resulting performance benefits—are approaching limits of diminishing returns. Accordingly, General Elec-tric and Siemens Westinghouse are using steam cooling for their very high temperature ATS turbines. Clemson University has conducted experiments in four test configura-tions to show that steam cooling per-formance is substantially improved by adding small quantities of water mist. Depending on the test con-figuration, an addition of 1 percent (by weight) of mist typically en-hanced cooling heat transfer by 50– 100 percent, and in best cases, by as much as 700 percent. By quanti-fying the potential benefits and de-fining key parameters, Clemson has provided the scientific underpin-ning to support development of a next generation closed-loop cooling system.
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