15.4 MCQ

Question 1

The stator vanes in an axial-flow compressor

a) convert pressure energy onto velocity energy
b) convert velocity energy into pressure energy
c) direct air into the first stage rotor vanes at the proper angle

Answer 1

b) convert velocity energy into pressure energy

Question 2

What units in a gas turbine engine aid in stabilisation of the compressor during low thrust engine operations?

a) Inlet guide vanes
b) Bleed air valves
c) Stator vanes

Answer 2

b) Bleed air valves

Question 3

Pneumatically operated bleed valves are normally spring loaded to the

a) closed position
b) mid-position
c) open position

Answer 3

c) open position

Question 4

Foreign object damage on compressor, when boroscoping is indicated by

a) flats
b) tip curl
c) nicks and scores

Answer 4

c) nicks and scores

Question 5

Bleed valves are

a) closed at high RPM
b) always slightly open
c) closed at low RPM

Answer 5

a) closed at high RPM

Question 6

The highest pressure in a gas turbine is

a) at the nozzle exit
b) at the burner exit
c) At the diffuser between compressor and combustion

Answer 6

c) At the diffuser between compressor and combustion

Question 7

If the LP compressor shaft severed

a) The engine will automatically shut down
b) the LP turbine will speed up and the LP compressor will slow down
c) the HP compressor will slow down

Answer 7

b) the LP turbine will speed up and the LP compressor will slow down

Question 8

An advantage of a centrifugal compressor is

a) it is unaffected by turbulence
b) it is robust and can stand some shock from ‘icing up’
c) it is dynamically balanced

Answer 8

b) it is robust and can stand some shock from ‘icing up’

Question 9

Variable inlet guide vanes prevent

a) compressor runaway
b) engine flame out at high speed
c) compressor stalling

Answer 9

c) compressor stalling

Question 10

An axial flow compressor surges when

a) early stages are stalled
b) all stages are stalled
c) later stages are stalled

Answer 10

b) all stages are stalled

Question 11

As a consequence of tapping air from the compressor, the EGT/ TGT will:

a) rise
b) remain constant
c) fall

Answer 11

a) rise

Question 12

Compressor air bleeds promote the flow of air through at low RPM by:

a) opening to allow air in
b) opening to allow air out
c) closing

Answer 12

b) opening to allow air out

Question 13

Compressor blades have reduced angle of attack at the tips

a) to prevent turbine stall
b) to increase the velocity
c) to allow uniform axial velocity

Answer 13

c) to allow uniform axial velocity

Question 14

Shrouding of stator blade tips is to

a) prevent tip turbulence
b) ensure adequate cooling
c) minimise vibration and tip losses

Answer 14

c) minimise vibration and tip losses

Question 15

Pressure rise across a twin spool axial flow compressor is

a) two to one
b) four to one
c) up to fifteen to one

Answer 15

c) up to fifteen to one

Question 16

What purpose do the diffuser vanes of a centrifugal compressor serve?

a) To increase the air velocity.
b) To convert pressure energy into kinetic energy
c) To convert kinetic energy into pressure energy.

Answer 16

c) To convert kinetic energy into pressure energy.

Question 17

In a reverse flow system the last stage of an axial flow compressor is often centrifugal, this is to

a) prevent compressor surge
b) provide initial turning of the airflow
c) increase the temperature rise

Answer 17

b) provide initial turning of the airflow

Question 18

The purpose of the inlet guide vanes on a centrifugal compressor is to

a) direct the air smoothly into the impeller
b) prevent damage by solid
c) provide initial dampening of the air

Answer 18

a) direct the air smoothly into the impeller

Question 19

The compression ratio of a jet engine is

a) the compressor outlet pressure divided by the number of compressor stages
b) the ratio between turbine pressure and compressor outlet pressure
c) the ratio between compressor inlet pressure and compressor outlet pressure

Answer 19

c) the ratio between compressor inlet pressure and compressor outlet pressure

Question 20

Variable inlet guide vanes help prevent:

c) compressor runaway
b) ice build up on compressor blades
c) compressor stalling

Answer 20

c) compressor stalling

Question 21

On modern front fan engines, to obtain thrust reversal, the:

a) hot and cold streams are reversed
b) cold stream is reversed
c) hot stream is reversed

Answer 21

b) cold stream is reversed

Question 22

A bleed valve:

a) controls air intake pressure
b) relieves compressor choking at low RPM
c) bleeds air from compressor for intake de-icing

Answer 22

b) relieves compressor choking at low RPM

Question 23

A compressor stage stalls when

a) smooth airflow is disrupted
b) compression ratio is too high
c) adiabatic temperature rise is too high

Answer 23

a) smooth airflow is disrupted

Question 24

During the high RPM range on an axial flow gas turbine engine, in what position are the variable intake guide vanes and bleed valves

a) at maximum swirl position, bleed valves closed
b) at maximum swirl position, bleed valves open
c) at minimum swirl position, bleed valves closed

Answer 24

c) at minimum swirl position, bleed valves closed

Question 25

pressure occurs

a) across stators only
b) across stators and rotors
c) across rotors only

Answer 25

b) across stators and rotors

Question 26

Inlet guide vanes are anti-iced with:

a) rubber boots
b) engine bleed air
c) thermal blankets

Answer 26

b) engine bleed air

Question 27

Run down time is indicative of

a) compressor malfunction
b) an FCU malfunction
c) the freedom of rotation of the compressor

Question 28

Compressor surge can be caused by:

a) over fuelling of the fuel tanks
b) rapid closing or opening of the throttle
c) prolonged engine running at high RPM

Answer 28

b) rapid closing or opening of the throttle

Question 29

What is the surge margin of an axial flow compressor?

a) The margin between the stall condition and the surge condition
b) The margin between the compressor working line and the surge line
c) The margin between minimum and maximum pressure ratio obtained at constant RPM

Answer 29

b) The margin between the compressor working line and the surge line

Question 30

If a compressor has a compression ratio of 9:1 and an intake compression of 2:1 what is the overall compression ratio?

a) 18:1
b) 11:1
c) 9:1 intake compression does not add to the overall compression ratio of the system

Answer 30

a) 18:1

Question 31

Why in an axial flow compressor is the cross sectional area of the compressor air duct (annulus) reduced at each stage:

a) to maintain the velocity of the air under rising pressure
b) to permit stronger, shorter blades to be used in the later stages
c) to decrease the velocity of the air rising under pressure

Answer 31

a) to maintain the velocity of the air under rising pressure

Question 32

at constant RPM the pressure ratio of the compressor and the temperature rise across the compressor

a) remains constant irrespective of height
b) increases with height
c) decrease with height

Answer 32

a) remains constant irrespective of height