Exhaust Noise Suppression 🔕

Question 1

Sources of noise

Answer 1

Fan
Compressor
Turbine
Combustion
Exhaust

Question 2

What is exhaust noise caused by and how can it be reduced

Answer 2

It’s the noise of friction from expelled air hitting still air.
It’s reduced by lowering jet exhaust velocity or by accelerating the mixing rate by using corrugate, lobe type or chevron nozzles

Question 3

What do convergent divergent nozzles do

Answer 3

Accelerates gases to supersonic speed

Question 4

What does a corrugated nozzle do

Answer 4

Allows free stream air to flow down the corrugating then mix with the hot air

Question 5

Lobe type nozzle function

Answer 5

Breaks the hot gas stream into smaller streams therefore increasing its mixing rate and spreading it over a greater area

Question 6

High frequency sound is produced by

Answer 6

Small eddies

Question 7

Low frequency sound is produced by

Answer 7

Large eddies

Question 8

Which is more loud to humans. Low or high frequency

Answer 8

Low frequency

Question 9

Chevron nozzle function

Answer 9

Has sawtoothed trailing edges of the engine which smoothes the mixing of hot exhaust with the atmosphere

Question 10

Acoustic liners are able to quieten what and are made of

Answer 10

Quieten the
inlet
Fan duct
Tips of rotors
They are made with porous or felt metal with a honeycomb structure