Primary function of exhaust system in jet engines
Accelerates exhaust gases to produce thrust
Primary function of exhaust system in turboprop engines
Guides gases overboard; only small thrust contribution
Primary function of exhaust system in APUs
Discharges gases overboard and reduces noise with mufflers
Main components of exhaust section
Exhaust cone, tailpipe, exhaust nozzle
Function of exhaust cone
Collects turbine gases and converts them into uniform flow
Effect of diverging passage in exhaust cone
Velocity decreases slightly, pressure increases
Exhaust cone structural elements
Outer duct, inner cone, radial hollow struts, tie rods
Purpose of exhaust cone struts
Support inner cone and straighten swirling gases
Purpose of tailpipe
Direct exhaust flow rearwards and safely overboard
Why tailpipes are semi-flexible
To allow thermal expansion and ease installation/maintenance
Purpose of insulation blankets
Reduce heat loss and limit heat radiation to aircraft structure
Insulation blanket construction
Aluminium foil layers separated by fibreglass
Two main exhaust nozzle designs
Converging and converging-diverging (C-D)
When converging nozzles are used
For subsonic exhaust gas velocities
When C-D nozzles are used
When exhaust gases reach or exceed sonic/supersonic velocity
Ducted fan turbofan exhaust
Core and fan airflow mixed into a single nozzle
Unducted fan turbofan exhaust
Separate nozzles for fan and core airflow
Purpose of core airflow nozzle in turbofans
Straighten and accelerate core exhaust
Thrust increase from converging nozzle
Approximately 15–20%
Exhaust thrust contribution in turboprops
About 10–15%
Other name for turboprop exhaust system
Tailpipe
Material of turboprop tailpipe
Simple stainless-steel duct
Cooling air effect in turboprop exhaust
Low pressure draws cooling air into exhaust stream
Characteristic of fixed exhaust nozzles
No moving parts
