15.04 Flashcards
What are the two ways you can compress air in an engine?
. Decrease the volume in a cylinder
. Make use of Bernoulli’s principe
What are the two main compressor components?
Rotor and stator
What does the rotor do?
Increase airflow energy
What does the stator do?
Guide the airflow
What are the set of stators in front a compressor stage called?
Inlet guide vanes
What are the stators called in the fan duct?
Outlet guide vanes
Where are centrifugal flow compressors usually found?
Small gas turbine engines such as APU
What is the pressure ratio of centrifugal flow compressors?
5:1
What is it called when two impellers are mounted face to face?
Double face compressor
What are some advantages of double face compressors?
Air can enter from front and back, higher airflow, saves weight
In an axial flow compressor what do the rotors do?
Increase velocity of the air but also slow it down, and increase static pressure
Why do we taper axial flow compressors?
Maintain velocity
The airflow in the axial compressor is smooth as long as?
The angle of attack on the rotor and stator vanes is small
What is airflow separation also called?
Compressor stall
What does compressor stall cause the airflow to do?
Airflow stops and slows down and sometimes reverses
What is a severe form of compressor stall?
Compressor surge
Where can compressor surge happen?
Fwd or aft compressor stage
What happens at compressor surge in the aft compressor?
Airflow decreases rapidly and reverses
What are some reasons for stall and surge in the compressor?
Dents or ice, damaged rotor blades, dirty blades, damaged compressor, damaged turbine
How can the compressor stall?
Engine is far below designed speed, incorrect acceleration or deceleration
What are the methods to avoid compressor stall and surge?
Compressor bleed valves, use dual or triple spool instead of single, variable compressor stator vanes
When are compressor bleed valves opened?
Low engine speeds
Each compressor rotor is driven by a separate?
Turbine
What is the most effective method to prevent stall?
Variable stator vanes
What does the spinner comb create?
Smooth aerodynamic fairing at engine inlet
What is the fan rotor disc made from?
Titanium alloy
What type of fitting is used on most aircraft?
Dovetail fitting
What is a loose fit necessary on engine parts?
Allow for sudden forces or torques
What forces act on rotor blades?
Centrifugal force and air loads
What does the shroud help the fan blade do?
Keeps deflection within safe limits
What can a wide chord blade withstand?
Foreign object damage because of its flexibility
On a turbofan engine the fan case has?
One or more ring elements
What do linings provide in the fan case?
Smooth surface for airflow
What do the holes on the fan case reduce?
Noise
When does unbalance occur on the fan rotor?
Material is removed from the blade
What is the best method when replacing a fan blade?
New blade with almost equal weight to the old one
What are balance weights used for on blades?
Compensate for imbalances
What seal do knife edges create?
Labyrinth seal
Each HP compressor always has a ….. seal
CDP
Why do inner ends of vane segments have an inner platform?
Reduce vibrations
Compressors with high compression ratios have?
Variable stator vanes
What does the HP compressor source?
Pressurised air for pneumatic system
What is bleed air supplied through?
Hollow stator vanes
