Reduction of Aircraft Gas Turbine Noise with New Synthetic Fuels and Sound Insulation Materials

The need to reduce the sound and vibration characteristics in the aerospace industry is continuously increasing because of the need to meet FAA regulations, to reduce noise pollution, and to improve customer satisfaction. To improve customer satisfaction, aircraft and engine manufacturers must work to control sound and vibration levels so that passengers do not experience discomfort during a flight. Sound and vibration characteristics of a fixed-wing aircraft with jet engines are composed of complex-frequency contents that challenge engineers in the development of quiet engine designs, aerodynamic bodies, and advanced sound-and vibration-attenuating materials. One of the noisiest parts of an aircraft, the gas turbine, was analyzed in this research. In Part 1 of this project, the use of alternative fuels in a gas turbine engine was investigated to determine whether those fuels have negative effects on sound and vibration levels. Three types of fuels were used: Jet A as the reference fuel, natural gas-derived S-8, and coal-derived isoparaffinic kerosene (IPK). The alternative fuels, S-8 and IPK, are Fischer-Tropsch process fuels. Overall sound and vibration characteristics of the alternative fuels presented a similar pattern across the frequency spectrum to those of the reference fuel, with the alternative fuels being slightly quieter. In Part 2, the sound path was treated by introducing sound-absorbing materials and investigating their acoustic performance. A melamine-based foam and soy-based foam were used in this research. Melamine is very lightweight, has excellent thermal endurance, and is hydrophobic. The soy-based foam was selected for its potential application in the aerospace industry to work toward a greener aircraft, in an effort to promote environmental sustainability. The soy-based material reduced the sound level by more than 20 dB(A) and presented better performance than the melamine at high frequencies.