Engines 2: Gas Turbine & Reciprocating Engines Flashcards
What is the purpose of an inlet duct?
To provide the proper amount of high pressure, turbulent-free air to the compressor
What are the two basic inlet designs?
Single entrance
Divided entrance
What shape is a subsonic inlet?
Divergent
What shape is a supersonic inlet?
Convergent-Divergent
The convergent shape initially reduces the airflow velocity to subsonic speeds (and increases pressure) and then the divergent shape increases pressure
What is the purpose of the compressor section?
- Supply high pressure air to the combustion chamber to satisfy combustion
Why doesn’t the Bernoulli Principle apply to the compressor section?
The compressor section is not a closed system so both airflow velocity and pressure increases
What are the three types of compressors?
Centrifugal
Axial
Axial-centrifugal
What are the three main parts to a centrifugal compressor? What does each part do?
Impeller - increase velocity, pressure, and total pressure
Diffuser - decreases velocity and increases pressure
Manifold - routes the air to the burner section
What are the two main parts to an axial compressor?
Rotors
Stators
What is the purpose of the burner section?
To ensure the proper mixing of air and fuel for good combustion
How is air entering the burner section (from the compressor) split up (percentages)?
Primary Air - 25%
Secondary Air - 75%
What is primary air used for?
To mix fuel and air for combustion
What is secondary air used for?
Cooling
Afterburning
Control of the flames
What is engine creep?
The elongation and deformation of turbine blades due to repeated heating over long periods of time
How can engine creep be minimized?
The “fir tree” method
The turbine blades are attached to the shaft in a fir tree shape that allows for expansion when heated
What is the purpose of the exhaust section?
To direct the flow of gases rearward to create high exit velocity and minimize turbulence
What are the main parts of the exhaust section?
Exhaust outer duct
Exhaust inner cone
Radial hollow struts (about 3 - 4)
What are the two types of exhaust nozzles?
Convergent
Variable exhaust nozzle
Remember, nozzles always increase velocity and that is the purpose of the exhaust section
What type of airflow does a convergent exhaust nozzle work for?
Subsonic airflow
What type of airflow does a variable geometry convergent-divergent nozzle work for?
Supersonic airflow
What is afterburning?
A method to increase max thrust available from an engine by 50% or more
Which air from the compressor is used for afterburning?
Secondary air
What are the four parts of the afterburner section?
Spray bars
Flame holders
Screech liner
Variable exhaust nozzle
What does a screech liner do?
Acts as a shock absorber to reduce pressure fluctuations and vibrations due to afterburner operations
