15.4 Flashcards
Compressors are made up of what?
Stators and rotors
What pressure do rotors increase?
Dynamic pressure
Stator vanes do what?
Slow airflow and increase pressure
Which is first in compressor stage out of rotors and stators?
Rotors
What are stator vanes also known as?
Inlet guide vanes (IGV)
Two types of compressors?
Axial flow
Centrifugal flow
What are the main components of a centrifugal compressor?
The impeller
The diffuser
The compressor manifold
Centrifugal flow compressors give what pressure ratio?
5:1
How many compressor stages are efficient?
2
Two impellers mounted back to back are known as what?
Double face compressor
What are the benefits of double face compressors?
Increase airflow due to two sides
Saves weight
Airflow in axial flow compressor is on what axis?
Horizontal axis
As pressure increases, density….
Increases
You taper axial flow compressors why?
Maintain air velocity
Why are compressors sensitive to airflow change?
Because compressors only have one operating condition for a given pressure ratio, rotational speed and airflow
What is the direction of airflow better called?
The resultant rotor inlet velocity
The resultant rotor inlet velocity is a result of what?
Air inlet velocity and rotor speed
The angle of attack changes when?
If rotor speed or inlet velocity changes
Compressor stall causes what for airflow in the compressor?
Causes airflow to slowdown, stop or reverse direction
A compressor surge is a very severe what?
Compressor stall
How is a compressor surge generated?
Rapid decrease of airflow onto blades
Then stall causes a blockage
That then causes low pressure zones
Surge is forward phase affects what?
Compressor blades
A surge in the aft stages could cause what to happen?
A reverse flow
Could occur from combustion chamber back to engine inlet
What are reasons for stalls and surges?
Dents or ice that cause disrupted airflow
Damaged rotor blades could cause disrupted airflow
Dirty compressor blades
How does a fast deceleration cause similar problems on dual to triple spool engines?
The rotor speed of high pressure compressor decreases faster than that of low pressure compressor
What is a method to avoid stalls or surges?
Use of dual or triple spools
Where are bleed valves found in compressors?
Found in mid and sometimes aft section of compressor
Why would you open the bleed valves at slow speeds?
So excessive airflow from forward stages can escape overboard
What are the low speed and high speed compressors driven by?
Their respective turbines in latter stages of engine
Variable stator vanes in compressor are used to prevent what?
Stall- Along vertical axis
The spinner cone is also known as what?
Compressor inlet or nose cone
Why do engines have a spinner cone?
-creates smooth aerodynamic fairing at engine inlet
-soft tip causes small imbalance to prevent ice build up
-heated on some engines
What type of attachment is the fan blade attachment?
Dovetailed fitting
Two loads on rotor blades?
Air loads
Centrifugal loads
What is the function of shrouds?
Keeps fan blade from deflection, within safe limits when heavy loads are on them
Converts energy of fluttering to friction
Why are wide chord fan blades more efficient than conventional blades?
They run with lower speed which reduces noise
Flexible
Can withstand FOD better than conventional
Low pressure compressor is also known as what?
Booster modules
Rotor drum of low pressure compressor is attached to what?
Fan disc
Between dovetail slots there are rings with sharp edges to create what?
A labyrinth seal
What are two methods of making shroud assembly?
Made from plain metal surfaces
Or individual segments
Shroud assembly segments are made up of what?
Filled with soft, abradable material where knife edges can cut in
On modern turbofan engine the fan cause has one or more ring elements, how are they bolted?
They’re bolted together to flanges
-Flanges help stiffen the case and prevent deformation
Acoustic panels provide what?
Smooth airflow
Reduce noise
The fan blade containment prevents what?
A fan blade from penetrating the fan case if it breaks during high speed operation
What are some things that would affect centrifugal force?
Rotor speed
Blade mass
Distance of the COG of fan blade from rotational axis
Moment weight can be given in what values?
Gram inches
CMG
ounce inches
What is the moment of weight?
The product of blade mass and distance of COG from rotational axis
How is moment of weight worked out?
Worked out by special blade scale
How is fan number one identified?
Index mark on fan disc or by an offset hole
Where are balance weights installed?
On fan disc or in spinner cone
A typical high pressure compressor consists of what?
Rotor drum
Forward hub
Rear hub
Rotor blades mounted on a drum
What is CDP?
Compressor discharge pressure
The compressor discharge pressure (CDP) prevents what?
Prevents the compressor discharge airflow from escaping into the bearing area below the combustion chamber
Blades held in by blade retainers prevents what?
Prevents axial movement
How are rotor blades secured?
Locking lug
The high pressure compressor case is split into what?
Front compressor case
Rear compressor case
The front compressor case supports what loads?
Structural loads
Torsion
Bending
Variable stator vanes have what at each end?
Trunnion
The HP compressor is a source of pressurised air for what?
Pneumatic systems
Engine related purposes
Bleed air is supplied through what?
Hollow stator vanes
Bleed manifolds collect bleed air and do what?
Supply it to consumers
What are the fixed axial flow compressor aerofoils in an aircraft gas turbine engine called?
Stators
What is the function of the stator vane assembly at the discharge end of a typical axial flow compressor?
To straighten airflow to eliminate turbulence
Where does the pressure increase in an axial compressor stage?
In both the rotor and the stator
Why do the compressor stators in a gas turbine engine act as diffusers?
To decrease velocity in the gas flow
What is known as the design point of a gas turbine engine?
Optimum RPM the engine can operate at
Which installed components can prevent compressor stalls?
Bleed valves, multiple spools and variable stator vanes
