Exhaust Systems and Thrust Reversal Flashcards
What is the purpose of the divergent exhaust nozzle?
By use of a cone from the turbine wheel to the exhaust
It reduces gas velocity and increases pressure to accelerate the gas stream away from the turbine.
Supported by turbine rear struts which straighten the gas stream, supports the cone, passages for rear bearing oil, and cooling air.
What is the purpose of the converging exhaust nozzle?
Propelling nozzle
Restores velocity and accelerates gasses to the local speed of sound to gain maximum thrust.
What exhaust ducts do transonic and supersonic aircraft use?
Convergent - divergent duct
What is the purpose of thrust reversal?
To shorten landing distance, reduce wheel braking and tyre and brake wear
What are the different methods of reverse thrust?
Reverse Exhaust Gas Stream
Reverse cold stream air
Explain Clamshell thrust reversers?
A hydraulic actuator deflects large metal plates into the jet efflux. Allowing the reverse of the exhaust gas stream.
Explain the Cascade Thrust reverser?
It directs airflow forward and outward by the application of blocker doors. Is a deflection of blades into the fan airflow to allows reversing the cold stream airflow. Exposing cascade vanes for the air to escape
Explain the aerodynamic blockage door reverse system?
Cold stream blocker doors actuated by an air motor.
When in forward thrust the cascade vanes are covered by the doors.
When reverse thrust is selected the actuation system moves the translating cowl rearwards and folds the blocker doors to blank off the cold stream final nozzle, thus diverting the air through the cascade vanes
Explain the mechanical blockage clamshell system?
It is the clamshell doors or bucketing system.
It is a pneumatically operated system.
It deflects the exhaust gases at the rear of the engine
On selection of reverse thrust doors rotate to uncover the ducts and close the normal gas stream exit. Cascade vanes then direct the gas stream outwards thus allowing the force on the doors to oppose the aircraft forward motion.
Explain the mechanical blockage bucket type door system?
Hydraulically actuated through pushrods to reverse the hot gas stream. When stowed a mechanical lock keeps it in position and when selected to reverse thrust the doors for a convergent-divergent final nozzle for the engine .
What are the main noise source in a jet engine?
Compressor
Exhaust Efflux
Transmission and gearbox
Propellor tip noise
What are noise reduction methods?
Mixing or reducing shear zones
Mixing hot and cold streamflow in the exhaust nozzle
Internal: Insulation of blankets and sandwich honeycomb panels
Which engine is louder the turbojet or turbofan?
The turbojet it has a large shear zone and the turbofan offers more mixing
