Gas turbines are widely used to produce power for a number of industrial applications. They emit extreme levels of noise due to the high horsepower output and high speed rotating blades. The major sources of noise are intake, exhaust and casing.
Intake noise is created by the interaction of the axial air compressor blades and stator, and is a function of pressure increase, number of blades and tip speed. The overall level of the intake noise is less than that produced by the exhaust, but its high frequency content sounds much louder than the higher amplitude, lower frequency exhaust noise. Exhaust noise has increased amplitude and is shifted to lower frequencies due to the combustion process. Casing noise is generated by the high speed misaligned mechanical components within the turbine housing radiating to the outer casing.
Turbines typically have inlet and exhaust sound power levels ranging from 120 dB to over 155 dB. The inlet and exhaust noises are principally aerodynamic sources. High aerodynamic turbulence and combustion noises are present in the exhaust that is principally broadband in nature. Parallel baffle silencers are traditionally used in the exhaust to address such noise. The performance reported for such silencers is often misleading as the gas in the exhaust is at an elevated temperature and the noise absorption performance of mineral wool is compromised in such conditions.