Aircraft Turbine Engine Sound and Vibrations Reduction for Increased Cabin Comfort

Aircraft in the field of commercial flights and military applications must meet high quality standards in order to enhance the quality of flight for civilian or stealth operation in Air Force applications. Gas turbines used in aircraft generate high levels of noise, urging designers to develop sound absorbing materials while meeting strict regulations such as fire resistance and lightness of the materials. The aerospace gas turbine in the Aero-engine laboratory in the Mechanical Engineering Dept. was used in this research to study the sound and vibrations during steady operation. Sample sound insulating materials were introduced to determine their absorbing capacity. The green materials used for testing were cotton based, recycled cottons composite, and fiberglass with aluminized quilted coating. The materials were all rated under Class A ASTM E84 Flammability Test Rating. A state-of-the-art Brüel & Kjær microphone was used to measure the sounds and the Pulse software was used to process the data. The frequency was set to 3700 Hz and the sound without insulation, with the cotton based insulation, with the recycled cotton composite, and with fiberglass were 94 dB, 81 dB, 78 dB and 64 dB, respectively. The aero-turbine was instrumented with the Bruel & Kjaer microphone and accelerometers to measure the sound and vibrations during a steady operation at 70,000RPM, fueled with Jet A. The measured data were processed in the Pulse software using Fast Fourier Transform (FFT). The sound level peaked at 127 dB at 8000 Hz, and the vibration acceleration peaked at 1,000 m/s2 at 13 kHz. High sound energy levels occurred at 3 kHz, 8 kHz, and 13 kHz. The vibration data also spiked at 3 kHz, 8 kHz and 13 kHz, indicating a strong correlation between sound and vibration. Further research will investigate sound absorption characteristics of the materials during the gas turbine operation, as the gas turbine generates high sound levels at several frequencies. All of the high sound energy levels appear well inside the range of human hearing prompting the need for proper absorption. This research can help us understand the effects of sound dampening better ultimately reducing excessive noise protecting the hearing of the people in close proximity while drastically reducing the noise pollution absorbed by the community