Chap - 2 Compressors Flashcards
(26 cards)
Two basic types of compressor
Centrifugal flow
Axial flow
What is the purpose of a compressor
To give a pre-determined pressure rise throughout the compressor
Principles of operation of a Centrifugal compressor
Pushes air into the centre of the impeller (the eye)
Centrifugal force then cause flow to go along divergent vanes
What is the diffuser section used for
Passages form divergent nozzles that convert kinetic energy into pressure energy
How much does the pressure rise in the impeller and in diffuser in compressor
50/50
What is done to maintain efficency in compressor
Prevent excessive air leakage between impeller and the casing.
Keeping their clearances as small as possible
Adv of Centrifugal compressor
Robust cheap to make
Low surge tendancy
Efficency over wide speed range
Withstand icing/FOD
Balancing is relatively easily
Simple to maintain
Dis Centrifugal compressor
Low compression ratio
Large frontal area
High impeller speeds
No straight through airflow
What compressor is this
Consists of one or more rotor assemblies that carry blades of aerofoil sections
Casing Incorporate the stator vanes
Multi stage unit. Pressure increase by each stage
Axial compressor
In axial compressor what does a stage consist off
Set of rotors
Set of stators
What term is this called
To maintain axial air velocity,the shape between the drum and outer Casing forms convergent duct
Cascade effect
What do these do
Rotor blade increases velocity
Stator blade decreases velocity
What is stagger angle
Rotor blades have a slight twist to make sure there is an even amount of work being done across the whole balde
Adv axial flow compressors
Higher compression ratio
Straight through airflow
Smaller frontal area
Capacity for further development
Dis for axial flow compressors
Complex
Expensive to build
Will not readily accept ram air
Slow to accelerate
Determine stall
A breakdown of airflow over one or more stages of the compressor
Determine surge
The event that occurs when compressor delivery air pressure is less than combustion pressure leading to hot combustion gases flowing backwards through the compressor
Identification of stall
Audible rumbling
Loss of RPM
High jet pipe temperature
Vibration
Identifications of surge
Loud bangs accompanied by flames from the intake
Rise in JPT
Lose of RPM
Extensive damage to the engine
How is airflow controlled
Inlet guide vanes
Variable stator vanes
Twin spool
Compressor discharge valve
What do inlet guide vanes achieve
Stationary or automatic
Guide the airflow onto the 1st stage rotors at correct AOA
What do Variable stator vanes achieve
Similar to IGV but operate over more stages
What does twin spool achieve
LP, HP Spool will run at different speeds
More flexibility
Less prone to stall and surge
What do compressor discharge valve achieve
It assists engine starting and helps to avoid stall and surge during start, acceleration and deceleration
Compensates for over efficency at low RPMs
