A mechanic studies the exhaust section of a turbojet engine located immediately aft of the last turbine stage. What is the primary function of the exhaust cone (tailcone) in this location?
- ATo accelerate exhaust gas velocity through a converging passage before it exits the engine
- BTo streamline and diffuse the gas flow around the rear bearing support while converting some velocity energy into pressure energy before final exhaust
- CTo mix bypass duct air with core exhaust gas for noise reduction
- DTo provide a mounting location for the thrust reverser actuation system
Show answer & explanationAnswer & explanation
Correct answer: B. To streamline and diffuse the gas flow around the rear bearing support while converting some velocity energy into pressure energy before final exhaust
The exhaust cone (tailcone) fairs over the rear bearing support strut assembly and provides an increasing flow area behind the last turbine stage. This diffuses the gas flow, converting a portion of the high-velocity, lower-pressure gas exiting the turbine into increased pressure before it enters the exhaust nozzle, improving the efficiency of the final expansion through the nozzle.
Why the other options are wrong
- A. Convergence occurs in the exhaust nozzle downstream, not in the diverging tailcone section.
- C. Mixing bypass and core air is the function of a mixer/lobed nozzle, not the tailcone.
- D. Thrust reverser mounting is typically on the fan case/cowl structure, not the tailcone.
Exhaust Cone (Tailcone)
A diverging fairing located aft of the last turbine stage that streamlines gas flow around the rear bearing support and diffuses velocity into pressure before the exhaust nozzle.
- Covers/fairs the rear bearing support strut
- Provides increasing flow area (diffuser) behind turbine
- Aids pressure recovery prior to nozzle expansion
Memory trick: The tailcone is a smooth umbrella diffusing flow around the bearing strut.