64.14 Turbine Engine Exhaust Section

64.14.2 State the function of the exhaust section.

The exhaust section directs the gases leaving the turbine safely out of the engine.

Its main functions are to:

• provide a smooth flow path for the exhaust gases;
• discharge the gases with minimum restriction and back pressure;
• direct the hot gases away from the engine, airframe and occupants; and
• in engines where exhaust thrust is required, accelerate the gases to produce thrust.

In a turbojet or turbofan engine, the exhaust system contributes significantly to thrust production.

In a turboshaft engine, most of the gas energy has already been extracted by the turbine to produce shaft power, so the exhaust normally produces little useful thrust.

64.14.4 Describe the exhaust gas flow through convergent and divergent passages.

The effect of a convergent or divergent passage depends on whether the gas flow is subsonic or supersonic.

For subsonic gas flow:

• a convergent passage causes the gas velocity to increase and its static pressure to decrease;
• a divergent passage causes the gas velocity to decrease and its static pressure to increase.