Chapter 3: Compressor Flashcards
compressor qualities
1) compressor pressure ratio
2) mass flow rate
3) rotational speed
4) adiabatic efficiency (no heat loss/gain)
components of centrifugal flow compressor
1) impeller (rotor)
2) diffuser (convert kinetic to pressure energy)
3) compressor manifold (transfer air to next stage)
what is the centrifugal compressor efficiency?
80% with compressor ratio of 4/5 to 1
advantages of centrifugal flow compressor
1) higher stage pressure ratio
2) simplicity & ruggedness of building
3) less drop in performance from dust on blades
4) shorter length for same pressure ratio
5) wider range of stable operation
disadvantages of centrifugal flow compressor
1) larger frontal area
2) more than 2 stages not practical due to energy loss between stages
types of centrifugal compressor to increase flow rate
double entry impeller
double entry centrifugal compressor
disadvantages of double entry impeller
1) implication of design to get air to rear impeller
2) volume of air not uniform from both inlet duct due to flow of air
disadvantages of double entry centrifugal compressor
1) energy lost in air (slows down to make turns from 1 impeller to another)
2) more weight & power needed to drive compressor
what is the compression ratio achieved with 2 centrifugal stages?
14/1
what happens if tip clearance for centrifugal compressor is too small?
vibration of engine (rubbing of impeller and stationary vanes)
what happens if tip clearance for centrifugal compressor is too large?
efficiency of compressor affected (some airflow will rotate with impeller without entering diffuser)
what does 1 stage of axial compressor consist of?
1 row of rotor & 1 row of stator
what is the compressor ratio for axial flow compressor?
1.2 per stage
what does an axial compressor consist of?
1) inlet guide vane (directs airflow to 1st rotor)
2) rotor
3) stator (stationary vanes)
how to count the number of stages in axial flow compressor when theres 7 rows?
IGV 1st row
1st rotor 1st stator
2nd rotor 2nd stator
3rd rotor 3rd stator
advantages of axial flow compressor
1) small frontal area
2) flow direction discharge suitable for multi staging
3) higher efficiency at high pressure ratio
disadvantages of axial flow compressor
1) complex mechanical design
2) higher possibility of surge
3) more prone to FOD
what does the rotor do in axial compressor?
impart motion to air (v increase), p increase due to divergent shape
what does the stator do in axial compressor?
transform part of velocity into pressure (divergent)
flow is straightened &directed to next stage at correct angle
solutions for perfect tip clearance for axial compressor
1) apply soft coat in edge tips on rotor blades (form own clearance)
2) coat inner layer surface with soft material (material worn away by blades without damaging it)
advantages of multi spool engine
1) higher compressor ratios
2) quick acceleration (less intertia of spools during starting)
3) low weight (less number of stages and smaller spool)
4) better control of stall characteristics
disadvantage of multi spool engine
bearings being the weakest link
what is compressor stall?
localised condition where one or few stages are affected by airflow disruption
what is compressor surge?
entire compressor suffers complete airflow disruption
signs of compressor stall/surge?
1) loss of power
2) vibration
3) rpm fluctuation
4) increase in EGT & noise
factors that lead to compressor stall/surge?
1) high power operation at low speed
2) abrupt change in altitude
3) air turbulence
4) deficiency air volume
5) rapid throttle movement
air quality & fuel quantity
mechanical malfunctions leading to compressor stall/surge
1) variable stator vane
2) fuel control unit
3) FOD
4) variable exhaust nozzle
effects of compressor stall/surge
1) increase in gas temp.
2) severe vibration (damage bearings)
3) violent noise
4) smoke/flame from exhaust
5) power drop
solution fo compressor surge/stall
1) place variable stator vane infront
2) add air bleed valve (relief pressure)
3) split spool
4) variable exhaust nozzle (input must be same as output air)
what compressor assembly does a turboshaft engine use?
axial centrifugal compressor
methods of fan blade attachment
1) dovetail
2) solid
3) fir tree
types of fan blades
1) narrow
2) wide-chord
which type of fan blade needs mid span support and why?
narrow fan blade, prevent aerodynamic instability and bending
what is shingling?
overlapping of mid span shrouds
disadvantage of mid span support on narrow blades
block some airflow & cause shingling
advantages of wide chord fan blade
1) fewer FOD ingestion
2) increase aerodynamic efficiency
3) lower noise level
4) decrease opportunity for surge
material of fan blade
sandwich titanium honeycomb & titanium panels
