15.7 Exhaust Flashcards
In general, what does the exhaust system do?
Guides the exhaust gases from the rear of the turbine into the atmosphere but the main task of the exhaust depends on the gas turbine engine
What is the main task of an exhaust on a jet engine?
To accelerate the airflow coming from the turbine to efficiently generate thrust
What is the main task of an exhaust turbo prop engine?
To safely guide the exhaust gases overboard
What is the main task of an exhaust on the APU?
To safely guide the exhaust gases overboard
What are the components of the exhaust section?
Cone, tailpipe and the exhaust nozzle
What does the exhaust cone do?
Collect the exhaust gases from the turbine section and gradually converts them into a solid flow of gases
What is a function of radial struts?
Support the inner cone and perform the important function of straightening the swirling exhaust gases
What is a small hole at the tip of the cone for?
This hole allows cooling air to be circulated from the aft end of the cone, where the pressure of the gases is relatively high, into the interior of the cone and consequently against the face of the turbine wheel
What is a bellow arrangement for?
Allowing movement in installation maintenance and thermal expansion which eliminate stress and warping
Two most common methods for protecting fuselage structure
Insulation blankets and shrouds
What are the two exhaust nozzle designs?
Converging design for subsonic gas velocities
Converging-diverging design for supersonic gas velocities
What are some features of insulation blankets?
Although these blankets protect the fuselage from heat radiation, they are used primarily to reduce heat loss from the exhaust system
What features do ducted fan engines have?
Ducted fan engines take the fan airflow and direct it through closed ducts along the engine. From there, it flows into a common exhaust nozzle. The core exhaust flow and the fan flow mix and flow from the engine through this mixed nozzle
What features do unducted fan engines have?
The unducted fan has two nozzles, one for the fan airflow and one for the core airflow. These both flow to ambient air separately from each other and have separate nozzles
How do the exhaust gases increase in velocity before they are discharged from the exhaust nozzle?
A converging nozzle
How much does the converging duct increase the thrust produced by?
15% - 20%
How much thrust does a turboprop plane nozzle provide?
Turboprop exhaust nozzles provide small amounts of thrust (10-15%) but are mainly used to discharge the exhaust gases from the aircraft
What are the two nozzle opening types?
Fixed, moveable
What are the fixed type features?
Simple, no moving parts
What is good about the fixed type exhaust nozzle?
The fixed type is the simplest of the two exhaust nozzles because there are no moving parts
What does a variable exhaust nozzle do?
A variable area exhaust nozzle is used when an augmenter or afterburner is used due to the increased mass of flow when the afterburner is activated
What does a convergent exhaust duct do?
The gas velocity is increased providing increased thrust
When is a convergent-divergent used?
Whenever the engine pressure ratio is high enough to produce exhaust gas velocities which might exceed Mach 1
What is the advantages of convergent-divergent ducts?
The advantage of a convergent-divergent nozzle is at high Mach numbers because of the resulting higher pressure ratio across the engine exhaust nozzle
What are the three noise sources?
Engineer intake, vibration from engine housing, engine exhaust
How is noise created within the jet engine?
Mixing of the exhaust gases with the atmosphere
Why do noise levels vary in an exhaust?
Very with engine frost and are proportional to the amount of work done
A large engine with a greater mass of air is what at the same thrust levels?
Quieter
What is the typical noise suppressor in current use?
Corrugated perimeter type or multi tube type
What does the acoustic linings surrounding the engine do?
Noise absorbing lining materials convert acoustic energy into heat
What did these acoustic lining skins normally consist of?
Porous skin supported by a honeycomb backing
When are thrust reverses used?
During landing on a wet, icy or snow covered runway
How do you thrust reverses work?
By producing the brake force by deflecting the exhaust grid in the opposite direction
Why can thrust reverses only be used on the ground?
Because a very dangerous aerodynamic changes that would cause a catastrophic situation
Where are clamshell type reverses used?
Older jet engines with a low bypass ratio
How do camshell type reverses work?
When they rotate to the reverse thrust position, they block off the normal flow path
Where are bucket type reverses found?
Old aircraft hydro operated also have low bypass ratio
Where are fan reverses found?
On turbofan engines with a high bass ratio
How are fan reverses operated?
Even pneumatically operate by drive movers or hydraulically operated by actuators in the engine cowling
How do pivoting door reversers work and how is it activated?
The pivoting-type reverser doors are hydraulically activated. They are flush with the engine cowling when the reverser is stowed and they close off the fan discharge airflow when they are deployed. This position deflects the fan airflow in a forward direction
What is thrust vectoring used for?
Military use thrust vectoring for manoeuvering in flight to change direction
Why can the engine compressor stall due to thrust reversers?
The engine compressor can stall because the airflow through the engine is disturbed by the deployed thrust reverser
When are reverse flow thrusters most effective?
At high speed shortly after touchdown
How do thrust reversers prevent FOD build up on critical parts of then engine?
Angle there airflow in ways away form critical parts of the engine and plane
