15.4 Compressors Flashcards
What are the two main components of a compressor?
-stator
-rotor
What are the two main types of compressor?
-centrifugal flow
-axial flow
What is an inlet guide vane and outlet guide vane?
Inlet - first row of stator vanes
Outlet - stator vanes in the fan duct for bypass
How many stages can a centrifugal compressor have ?
2
How many stages can a centrifugal compressor have ?
2
What is the rise per stage on a centrifugal compressor?
8:1
What are the two main functional elements of a centrifugal compressor?
Impeller
Diffuser
What is the function of the impeller?
Accelerating air outwardly to the diffuser
What are the two types of impeller available?
Single or double entry
Where are centrifugal compressors typically used?
Turbo prop
Turbo shaft
What are the shapes of axial compressor blades?
Aerofoil
What does the gradual decrease in diameter allow for in an axial flow compressor?
Steady axial velocity as pressure and density increase
What does a multi spool compressor allow for?
Maximum possible compression ratio
What does the fan become in a three spool engine?
A low pressure compressor
What is another role of stator in a compressor?
Direct airflow straight
What ratio will a stage on an axial compressor achieve?
1:1-1:2
What are the advantages of an axial compressor?
-negligible losses over stages increasing pressure
-higher RAM air efficiency
What is the purpose of moment weighing?
Blade mass and distance of centre of gravity must be measured to account for manufacturing defects
What is recorded on blade root?
Moment weight
Serial number
Part number
What is the purpose of computerised fan blade distribution?
Using a computer to show where the optimum blade layout is
Where not possible to get a fan blade of close enough weight what must be done?
Swap in pairs and use balance screws
What is the relationship between rotor speed and angle of attack?
The higher the rotor speed means the larger the angle of attack
What is the relationship between airspeed and angle of attack?
Higher airspeed means smaller angle of attack
Why is a low angle of attack ideal?
It allows smooth airflow
What causes compressor stall?
High angle of attack causes airflow separation in the rotor and vortices form causing slow, stopped or reversed flow
What is compressor surge?
-rapid decrease in airflow
-stall causes a blockage causing subsequent stalls
-low pressure zones reverse airflow
What can cause stall and surge?
-damaged or dirty blades
-damaged or dirty inlet
-damaged or broken compressor
To low idle speed
Acceleration or deceleration incorrectly
How do bleed valves avoid stall?
-Mid and aft compressor locations
-Excessive air from forward stages can escape
-Open at low engine speeds
How do variable stator/ variable inlet guide vanes prevent stall?
They are the most effective
They move along vertical axis
Optimum angle of attack can be achieved
What is the axial flow compression per stage?
1.3:1
