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Engine noise suppressed

Engine noise suppressed(Basic)

 Engine noise suppressed(Basic)

To understand the problem of engine noise suppression, it is necessary to have a working knowledge of the noise sources and their relative importance. The significant sources originate in the fan or compressor, the turbine, and the exhaust jet or
jets. These noise sources obey different laws and mechanisms of generation, but all increase, to a varying degree, with greater relative airflow velocity. Exhaust jet noise varies by a larger factor than the compressor or turbine noise, therefore a reduction in
exhaust jet velocity has a stronger influence than an equivalent reduction in compressor and turbine blade speeds. Jet exhaust noise is caused by the violent and hence extremely turbulent mixing of the exhaust gases with the atmosphere and is influenced by the shearing action caused by the relative speed
between the exhaust jet and the atmosphere. The small eddies created near the exhaust duct cause high-frequency noise but downstream of the exhaust jet the larger eddies create low-frequency noise. Additionally, when the exhaust jet velocity exceeds the local speed of sound, a regular shock pattern is formed
 within the exhaust jet core. This produces a discrete (single frequency) tone and selective amplification of the mixing noise.

CREDIT BY Andrew naidu
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