M15.4 Flashcards
What are the 2 main components of the compressor?
Compressor rotor
Compressor stator
What does the compressor rotor do to the energy?
Increases its energy
What does the compressor rotor do?
Rotates around the axis of the compressor the rotator blades suck in air and push it to the outlet side of the rotor
What does the stator do to the airflow?
Guide and slow the airflow to cause an increase in pressure
What is the compressor stage?
A combination of a rotor and stator
What is the first part of the compressor stage, rotor or stator?
Rotor
What type of combustion chamber is on turbo shaft engines?
Reverse flow combustion chamber
What is a inlet guide vane?
The first stator vane of the compressor
What is the outlet guide vane?
The stator vanes that are in the fan duct
(Or the last stator vane of the compressor)
What does the inlet/outlet compressor case do?
Give support to the compressor rotor bearings as well as improve and straighten airflow in and out of the compressor
What are the 2 types of compressor?
The axial flow compressor
The centrifugal flow compressor
Where is the centrifugal flow compressor usually found?
On small GTE’s such as APU
What are the main components of the centrifugal flow compressor?
Impeller
Diffuser
Compressor manifold
How does the centrifugal compressor work?
The rotation of the impeller sucks air in and pushes air outwards by centrifugal force to increase velocity and the energy of air
What is the ratio for centrifugal flow compressor?
5:1
Why do some engines use multiple compressor stages?
To give higher pressure
How many stages are efficient in a multi stage compressor?
And why?
2
Because of the pressure decrease that occurs when the airflow changes direction between stages
What is the double face compressor?
When 2 impellers are mounted face to face
What is the advantage and disadvantage of the double face compressor?
It doesn’t give higher pressure but it has a higher airflow as well as being light weight
Where Does airflow flow in a axial flow compressor?
Along the horizontal axis
What’s special about the rotor blades in a axial flow compressor?
And what does this allow?
They are aerodynamically shaped
Allows a smoother airflow
Why are the channels between the rotor blades diffusers?
To increase velocity and to slow airflow down to increase the static pressure
What is the ratio for axial flow compressor?
1.3:1
Why does the air need less volume in a axial flow compressor?
Because as the pressure increases the density does as well
Why is the case of a axial flow compressor tapered?
To increase dynamic pressure and maintain velocity
What does a divergent duct do?
Creates dynamic and static airflow in one
What are axial and centrifugal compressors sensitive to?
Changes in airflow
What is the design point?
Where the airflow in the compressor is perfect matched
How big does the angle of attack have to be on the blade of the compressor?
Very small
What determines the angle of attake on a compressor?
The resultant
What is needed for a smooth airflow into the rotor?
The correct relationship between the inlet velocity and rotor speed
The direction of airflow in a compressor is called what?
Resultant rotor inlet velocity
The stator vanes in the compressor do what?
Slow the airflow and guide it to the next rotor stage
What happens to airflow in a compressor stall?
Angle of attack increases and inlet air velocity decreases
The airflow will also separate from the aero foil and cause a turbulent vortex
A compressor stall causes the airflow to do what?
Slow down, stop or reverse
What is compressor surge?
When stall becomes strong and affects all compressor stages
What happens to low pressure zones during compressor surge?
Airflow will stop and reverse its direction
Where can surge occur?
Fwd or aft compressor stages
Surge in the aft stages of compressor does what?
Develops very rapidly over a large part of the compressor
Surge in fwd part of compressor does what?
Affects only a small part of the compressor blades
What happens to airflow when compressor surge occurs?
Airflow will collapse and build up again at very short intervals
What does compressor surge come with?
Heavy vibrations and loud banging noises
What 3 things happens to engine parameters during compressor surge?
Thrust will decrease
Engine fluctuates
EGT rises
Why does surge or stall happen?
Damaged rotor blades and stator vanes
Dents or ice on inlet
Dirty compressor blades
Broken combustor components
What are the 2 ultimate reasons for stall or surge
If speed of engine is below design speed
Fast deceleration (meaning compressor rotates too slow)
During fast deaccelration how does surge happen?
Because the speed of the hp compressor decreases faster then lp compressor
What are the 3 methods to avoid surge and stall?
Compressor bleed valves
Duel or Triple spool rotors instead of a single spool
Variable compressor stator vanes
Where are compressor bleed vanes found?
In mid or aft section of compressor
When does the compressor bleed valve open?
At low engine speeds
What causes a big loss in efficiency in a compressor?
When airflow is compressed first and then blown overboard
On dual spool engines the fwd part is called what?
Lp compressor or N1 compressor
On a dual spool engine the aft part is called what?
Hp compressor or N2 compressor
What is the compressor rotor driven by?
A turbine
Why does a multi spool engine have great acceleration capability?
Because of the small rotor mass of the split rotors
What is the most efficient method to prevent a stall?
Variable stator vanes
Where are variable stator vanes found?
In the fwd area of the hp compressor
What is the advantage of variable stator vanes?
a optimum angle of attack on the following rotor blades can be reached at every engine speed
What is the disadvantage of a varable stator vane?
It needs a complicated control mechanism
What are the 4 sub modules of the lp compressor and fan module?
Fan rotor and booster module
Number 1 and 2 bearing module
Inlet gear box
Fan frame module
The spinner cone is also known as what?
Compressor inlet or nose cone
What does the spinner cone do?
Covers end of fan rotor disc & creates a smooth aerodynamic fairing at engine inlet
Where can weights be added to the spinner cone?
Mounting bolts or the threaded inserts
What fitting is used to attach fan blades?
A dovetail fitting
Why is a loose fit needed when mounting fan blades?
So any sudden forces or torque don’t exceed the allowable stress limits of the fan blades
What are the 2 loads that act on the rotor blades?
Air loads
Centrifugal loads
What do shrouds do?
Keep fan blade deflection within safe limits when heavy loads act on them.
How do shrouds work?
By sliding contact surfaces of shrouds to convert fluctuating blade energy into friction energy to dampen blade friction.
What type of fan blade is found on most modern GTE’s?
Wide chord fan blades.
What are the advantages of a wide chord fan blade?
More efficient
Run at lower speeds
Very flexible
Withstand FOD better
What is the LP compressor also called?
Booster module
What is the rotor drum connected to in a LP compressor?
Fan disc
The rotor drum has what sort of slots around its circumference?
Dove tail
What does the rotor drum hold and how?
The blades with a dovetail fitting
How are the stator made up?
Either plain metal or individual segments
The LP compressor case assembly does what?
Encloses the LP compressor rotor and supports the vanes of the LP compressor
.
Vanes are fitted to shrouds between rotor stages
What is the split stator case?
All vanes are installed in 2 stator halves and bolted together afterwards
On modern turbo fan engine cases how many ring elements are there?
1 or more
What do flanges do on the outer surface of a case?
Help to stiffen the case and prevent deformation
What are acoustic panels?
Linings that reduce noise
Why must you be careful with the outer surface of the acoustic lining?
It can be easily damaged with tools and FOD
The outer guide vanes are installed where?
In the fan duct or behind the fan blades
what is the purpose of the abradable shroud?
A soft material which prevents damage to fan blades if they come in contact with the shroud
Why are the tips of the fan blades able to cut into the shroud?
So the blades can run with a very small tip clearance and max efficiency
What is the purpose of the fan blade containment?
Prevents blade from penetrating fan case if it breaks
Where is the fan frame located?
In between the LP and HP compressors
What does the centre hub do?
Supports spool fwd bearing and houses internal gearbox
What does the structure around the central hub do?
Diverts the air into the core
What does the outer core of the fan frame give support to?
Engine equipment
The fan frame strut connects what?
Internal and external section of the fan frame
When does imbalance of a fan rotor occur?
If material is removed from a blade
Or
There’s a difference in weight of blades
Moment of weight changes with what?
Blade mass
Position of CofG of fan blade
Centrifugal force of the fan blade depends on what 3 things?
Rotor speed
Blade mass
Distance of CofG of fan blade from rotational axis
Moment weight may be given in what?
Gram inches
Cmg
Oz inches
A blade root will be marked with what?
Part number
Serial number
Moment weight
What can you add to blades to get them balanced?
Balance weights
What is the of set mounting hole used for?
To position the spinner cone in the correct position
How is the disc rotor assembled on the HP compressor?
From individual discs and spacers
How are rotor hubs in the HP compressor bolted?
With bolts or long tie rods
What does the labyrinth seal prevent?
Reverse air flow through the gap between rotor and stator
CDP?
Compressor discharge pressure
CDP prevents what?
Compressor discharge airflow escaping into bearing area
The HP compressor case of a turbofan is split up into what?
Front compressor case and rear compressor case
What is the front compressor case made up of?
2 halves with a bolted centreline joint
What does the front compressor case support?
Structural loads
(Bending and torsion)
How are stator vanes usually installed?
In circumferential dovetail slots
Why do the inner ends of the stator vane segments have a inner platform?
To minimise vibrations caused by the airflow
Compressors with a high compression ratio have what?
Variable stator vanes
Variable stator vanes have what at each end?
A trunnion
Why do all variable stator vanes move simultaneously?
Because they are installed together with actuation leavers which are connected to a actuation ring
Bleed air is supplied to the compressor via what?
Hollow stator vanes
