Compressors Flashcards
Two main commoners in a compressor
Rotor and stator
What’s a rotor used for
Increase velocity
What’s a stator used for
Guide airflow to next rotor and increase static pressure
What different about a turbo shaft engine
Uses twin spool engine with reverse flow combustion
What’s the two types of stator vanes
First is called inlet guide vane
Second is called outlet guide vane
What are the two types of cases
Inlet and outlet case
What’s the purpose of a case
Give support for compressed rotor bearings and improve & strength airflow in and out of compressors
Two types of compressors
Axial flow and Centrifugal flow
Where is centrifugal flow compressors used
Small GTE such as apus
Centrifugal compressor pressure ratio
5:1
What are the parts of the centrifugal compressor
Impeller which is a rotor
Diffuser which is a stator
Compressor manifold which is compressor housing
What is maximum stages in a centrifugal compressor
Maximum 2 stages anymore and it becomes inefficient due to pressure decrease when air changes direction
What’s the purpose of a double face compressor
Higher airflow because air can enter from both sides without changing pressure
Saves weight and has a smaller frontal area
What axis is axial flow along
Horizontal
How is air slowed down in axial flow
Use of divergent duct which is a diffuser like shape
Axial flow pressure ratio
1:3:1
What’s the need for a tapered compressor case
Reduces cross sectional area which maintains axial velocity
What is design point
Optimum operating condition for a given pressure ratio , rotational speed and airflow
What is resultant rotor inlet velocity
Direction of airflow
Sum of air inlet velocity and rotor speed
Why is a small angle of attack to blades necessary
Allows airflow into rotor to be smooth
What does a stator do in an axial compressor
Decelerate airflow and guide to next compressor
What is the condition for speed for normal flow in an axial compressor
Only optimum at one compressor speed
What is the compressor stage
Rotor and stator together
What happens during stall
Airflow separates from compressor aero foils and causes turbulent vortex
What happens during compressor stall
Airflow slows down , stops or going in reverse direction
When does compressor stall occur
Low speed
What is a surge
Severe form of stall and happens in fwd or aft of compressor stage
What happens to thrust in a surge
It decreases which causes engine speed fluctuations and gas exhaust temperature to increase
What are the reasons for stall or surge
1.Damaged rotor blades or stator vanes
2.Dents or ice in engine inlet
3.Dirty compressor blades
4.Damaged turbine or broken objects in exhaust
When can engine stall
If engine speed is too far behind design speed
What are the 3 methods of airflow control
- Compressor bleed valve
- Dual or triple spool rotor
- Variable compressor stator vanes
What is most effective method of airflow control
Variable stator vanes
What’s a disadvantage of variable stator vane
Needs a complicated control mechanism
What does the Low Pressure Compressor & Turbine coupling do
Attaches and secures LPC Rotor to LPT shaft
What the purpose of a fan stator case
Flow path for discharge air
What type of component is a intermediate case
Major structural component
Spinner cone shape
Curved front or sharp tip
Spinner cone other names
Nose cone or compressor inlet cone
What does the spinner cone do
Creates smooth aerodynamic fairing at engine inlet
What material is a fan blade disc and where is it attached
Titanium alloy and fwd rotor shaft and rotor drum of the LPC
What shape is fan blade attachment
Dove tail fitting and a loose fit is necessary
What loads are on rotor blades
Air loads in the horizontal direction & centrifugal loads
What does a midspan shroud do
Keep flan blade deflection within safe limits
What does converting energy of fluttering blade into friction do
Dampens the fluttering
What is the LP compressor
Booster module
What slots does a drum have
Dovetail
What are the rings with sharp edges for in a drum
For the labyrinth seal which is used for efficiency
What’s the good thing about wide chord fan blades
More efficient and can be used at Low speeds while producing less noise
What’s the LPC stator case for
Enclosed rotor and supports stator vane
What the two types of construction methods for a LPC stator case
Closed and split
How many ring elements does a turbofan engine have
One or more
What’s the purpose of a flange
Stiffen case and prevent deformation
What does an acoustic panel do
Smooth surface for airflow & small holes on surface reduce noise
Construction of ring element
Honeycomb construction with Kevlar layers
What is an abradable shroud
Soft material that prevents damage if blades come into contact with shroud
When can fan blade be cut into shroud
High speeds , abradable shroud allowlist very small tip clearance for maximum efficiency
Where is the intermediate case and what’s another name for it
Positioned between LP and HP compressor and is know as fan frame
What does the intermediate case do
House variable bleed valves which protect against LPC surge
How are struts shaped
Aerodynamically shaped in areas where they reach through the fan duct and core engine duct
When does imbalance occur
Due to difference in momentum weighs between fan blades
Centrifugal force parameters
- Rotor speed
- Blade mass
- Distance of CoG from rotational axis
What is the moment weight measured
- Gram inches
- Cmg
- Oz inches
How do you know what method of fan blade change to do
Method is proposed by manufacturer
What’s the best method of fan blade change
Replace with the same moment weigh or as close of possible
Why do we offset the mounting hole
Makes tire spinner is in correct position
How is a rotor assembled in the HP compressor
By two or more integral drums or bolted to adjacent drum and separate disc
What’s does CDP seal do
Prevents discharge airflow going to bearing area below the combustion chamber
What is design principle in stator assembly
Allows closer clearances between blade lips and compressor case
How are stator vanes grouped
Into segments
How are stator frames installed
As single vanes
What’s the inner ends of the vane segment platform for
Minimise vibrations caused by airflow
On a variable stator vane where is the trunnion
Each end
What’s the outer trunnion for
Fits into a hole in the compressor case
How are trunnions installed
Together with an actuation lever
How are levers connected
To the same ring so they move simultaneously
Who selects position of high speed pick ups on the HPC
Manufacture
What is the source of bleed air for the pneumatic system
HPC
How is bleed air supplied
Hollow stator vanes or holes in outer platform off stator vanes
Where are bleed pick up holes located
Entire circumstance of case
What does the bleed manifold do
Collects air form pick up holes and supples it to the consumers
