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Static gas temperature decrease when flowing at a subsonic speed through a jet engine exhaust nozzle because the:
  • A
    ambient air cools the exhaust casing.
  • B
    static pressure increases when passing the nozzle.
  • C
    exhaust nozzle is convergent.
  • D
    velocity of the gas stream decreases.
The propelling nozzle directs the exhaust gas aft and regulates the gas stream flow. It must be designed to obtain the correct balance of pressure and velocity to prevent flow separation. That’s why most of the time it is converging so that it can induce a decrease in pressure and temperature and an increase in exhaust gases velocity (kinetic energy) resulting in a higher thrust. The acceleration of the flow by the propelling nozzle can somehow disturb the airflow, so it is positioned at a distance from the jet pipe where the disturbances won’t cause flow separation.
 

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