M15.7 (exhausts) Flashcards
On a turboprop engine how much thrust is provided by the exhaust system?
Only a small amount
What is the purpose of the muffler?
To reduce noise coming from the exhaust
What is the exhaust tube called?
Exhaust duct or tail pipe
Where would you usually find a long exhaust duct?
Old a/c where engines are installed directly under the wing
What’s the advantage of the common exhaust nozzle?
Gives a higher propulsion efficiency
What is the disadvantage of the common exhaust nozzle?
Increase weight of the engine
What are the 2 exhaust streams? And where do they come from?
Hot gas from primary nozzle
Cold fan air from secondary nozzle
What does the exhaust gas mixer do?
Improves mixing of hot and cold gasses to get a higher proposition
What’s the purpose of the exhaust cone?
Guides the discharge flow and prevents turbulence as well as gas re-ingestion
What must happen to gas flow in the exhaust nozzle?
Must expand fully to give a laminar vortex free and axially oriented gas flow
What is exhaust airflow caused by?
Pressure ratio between turbine discharge and ambient pressure
Increasing engine speed does what to the pressure ratio?
Increases it
What happens if you increase the pressure ratio too much?
It will get to a point where it’s impossible to get more air through the smallest area of the nozzle
What is the maximum pressure ratio?
2:1
What is chocked condition?
The smallest in the area of the nozzle the exhaust gas velocity equals the speed of sound
When would a convergent duct be used?
When there’s a pressure ratio of more then 2:1
Why must convergent dusts be variable?
Because their sensitive to changes in rpm
What type of engines will you find high exhaust gasses?
Turbojet engines and old turbofan engines
Why must high exhaust gasses be avoided?
Because they decrease the proposition efficacy
Engine noise is expressed in what units?
EPNdb
EPNdb?
Effective Perceived Noise deciBel
How is a reduction of internal noise achieved?
By reducing the airflow disruption by optimising the number of blades and vanes in the compressor
What is used in airflow linings to reduce noise and how is it achieved?
Honey comb acoustic liners that convert noise energy into heat energy
What are the 2 types of noise absorbent liner?
Single layer liner
Double layer liner
How can external noises be reduced?
If mixing with the atmosphere is performed in a short region done by increasing the contact area of the exhaust gas stream
