The noise of jet airplanes in flight comes from two components: noise from powertrains and aerodynamic noise.
THE NOISE OF POWERTRAINS
Noise from the rotating parts of the engine (upstream and downstream blowers, compressor and turbine),
It’s about : jet noise (combustion noise and internal noise)
The jet noise is caused by the generation of strong turbulence in the area where the hot high pressure gases ejected from the engine nozzle mix with the ambient air.
AERODYNAMIC NOISE
Aerodynamic noise is caused by the aerodynamic turbulence created around the aircraft. The noise of flaps, slats and landing gear are examples.
Given the progress made on the engines, this source of noise becomes as important, or even greater than the noise of the engine for the landing phases with a large development of the flaps.
The noise produced by aircraft when they are parked (engine tests) or when they are taxiing on the ground can also be a source of noise pollution for those living near aerodromes.
Author – Mfongan Pascal
Electronic Engineer for Aviation Safety Systems