Chapter 3: Compressor

Question 1

compressor qualities

Answer 1

1) compressor pressure ratio
2) mass flow rate
3) rotational speed
4) adiabatic efficiency (no heat loss/gain)

Question 2

components of centrifugal flow compressor

Answer 2

1) impeller (rotor)
2) diffuser (convert kinetic to pressure energy)
3) compressor manifold (transfer air to next stage)

Question 3

what is the centrifugal compressor efficiency?

Answer 3

80% with compressor ratio of 4/5 to 1

Question 4

advantages of centrifugal flow compressor

Answer 4

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

Question 5

disadvantages of centrifugal flow compressor

Answer 5

1) larger frontal area
2) more than 2 stages not practical due to energy loss between stages

Question 6

types of centrifugal compressor to increase flow rate

Answer 6

double entry impeller

double entry centrifugal compressor

Question 7

disadvantages of double entry impeller

Answer 7

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

Question 8

disadvantages of double entry centrifugal compressor

Answer 8

1) energy lost in air (slows down to make turns from 1 impeller to another)
2) more weight & power needed to drive compressor

Question 9

what is the compression ratio achieved with 2 centrifugal stages?

Answer 9

14/1

Question 10

what happens if tip clearance for centrifugal compressor is too small?

Answer 10

vibration of engine (rubbing of impeller and stationary vanes)

Question 11

what happens if tip clearance for centrifugal compressor is too large?

Answer 11

efficiency of compressor affected (some airflow will rotate with impeller without entering diffuser)

Question 12

what does 1 stage of axial compressor consist of?

Answer 12

1 row of rotor & 1 row of stator

Question 13

what is the compressor ratio for axial flow compressor?

Answer 13

1.2 per stage

Question 14

what does an axial compressor consist of?

Answer 14

1) inlet guide vane (directs airflow to 1st rotor)
2) rotor
3) stator (stationary vanes)

Question 15

how to count the number of stages in axial flow compressor when theres 7 rows?

Answer 15

IGV 1st row

1st rotor 1st stator
2nd rotor 2nd stator
3rd rotor 3rd stator

Question 16

advantages of axial flow compressor

Answer 16

1) small frontal area
2) flow direction discharge suitable for multi staging
3) higher efficiency at high pressure ratio

Question 17

disadvantages of axial flow compressor

Answer 17

1) complex mechanical design
2) higher possibility of surge
3) more prone to FOD

Question 18

what does the rotor do in axial compressor?

Answer 18

impart motion to air (v increase), p increase due to divergent shape

Question 19

what does the stator do in axial compressor?

Answer 19

transform part of velocity into pressure (divergent)

flow is straightened &directed to next stage at correct angle

Question 20

solutions for perfect tip clearance for axial compressor

Answer 20

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)

Question 21

advantages of multi spool engine

Answer 21

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

Question 22

disadvantage of multi spool engine

Answer 22

bearings being the weakest link

Question 23

what is compressor stall?

Answer 23

localised condition where one or few stages are affected by airflow disruption

Question 24

what is compressor surge?

Answer 24

entire compressor suffers complete airflow disruption

Question 25

signs of compressor stall/surge?

Answer 25

1) loss of power
2) vibration
3) rpm fluctuation
4) increase in EGT & noise

Question 26

factors that lead to compressor stall/surge?

Answer 26

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

Question 27

mechanical malfunctions leading to compressor stall/surge

Answer 27

1) variable stator vane
2) fuel control unit
3) FOD
4) variable exhaust nozzle

Question 28

effects of compressor stall/surge

Answer 28

1) increase in gas temp.
2) severe vibration (damage bearings)
3) violent noise
4) smoke/flame from exhaust
5) power drop

Question 29

solution fo compressor surge/stall

Answer 29

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)

Question 30

what compressor assembly does a turboshaft engine use?

Answer 30

axial centrifugal compressor

Question 31

methods of fan blade attachment

Answer 31

1) dovetail
2) solid
3) fir tree

Question 32

types of fan blades

Answer 32

1) narrow
2) wide-chord

Question 33

which type of fan blade needs mid span support and why?

Answer 33

narrow fan blade, prevent aerodynamic instability and bending

Question 34

what is shingling?

Answer 34

overlapping of mid span shrouds

Question 35

disadvantage of mid span support on narrow blades

Answer 35

block some airflow & cause shingling

Question 36

advantages of wide chord fan blade

Answer 36

1) fewer FOD ingestion
2) increase aerodynamic efficiency
3) lower noise level
4) decrease opportunity for surge

Question 37

material of fan blade

Answer 37

sandwich titanium honeycomb & titanium panels