15.4 MCQ Flashcards
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
b) convert velocity energy into pressure energy
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
b) Bleed air valves
Pneumatically operated bleed valves are normally spring loaded to the
a) closed position
b) mid-position
c) open position
c) open position
Foreign object damage on compressor, when boroscoping is indicated by
a) flats
b) tip curl
c) nicks and scores
c) nicks and scores
Bleed valves are
a) closed at high RPM
b) always slightly open
c) closed at low RPM
a) closed at high RPM
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
c) At the diffuser between compressor and combustion
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
b) the LP turbine will speed up and the LP compressor will slow down
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
b) it is robust and can stand some shock from ‘icing up’
Variable inlet guide vanes prevent
a) compressor runaway
b) engine flame out at high speed
c) compressor stalling
c) compressor stalling
An axial flow compressor surges when
a) early stages are stalled
b) all stages are stalled
c) later stages are stalled
b) all stages are stalled
As a consequence of tapping air from the compressor, the EGT/ TGT will:
a) rise
b) remain constant
c) fall
a) rise
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
b) opening to allow air out
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
c) to allow uniform axial velocity
Shrouding of stator blade tips is to
a) prevent tip turbulence
b) ensure adequate cooling
c) minimise vibration and tip losses
c) minimise vibration and tip losses
Pressure rise across a twin spool axial flow compressor is
a) two to one
b) four to one
c) up to fifteen to one
c) up to fifteen to one
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.
c) To convert kinetic energy into pressure energy.
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
b) provide initial turning of the airflow
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
a) direct the air smoothly into the impeller
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
c) the ratio between compressor inlet pressure and compressor outlet pressure
Variable inlet guide vanes help prevent:
c) compressor runaway
b) ice build up on compressor blades
c) compressor stalling
c) compressor stalling
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
b) cold stream is reversed
A bleed valve:
a) controls air intake pressure
b) relieves compressor choking at low RPM
c) bleeds air from compressor for intake de-icing
b) relieves compressor choking at low RPM
A compressor stage stalls when
a) smooth airflow is disrupted
b) compression ratio is too high
c) adiabatic temperature rise is too high
a) smooth airflow is disrupted
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
c) at minimum swirl position, bleed valves closed
pressure occurs
a) across stators only
b) across stators and rotors
c) across rotors only
b) across stators and rotors
Inlet guide vanes are anti-iced with:
a) rubber boots
b) engine bleed air
c) thermal blankets
b) engine bleed air
Run down time is indicative of
a) compressor malfunction
b) an FCU malfunction
c) the freedom of rotation of the compressor
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
b) rapid closing or opening of the throttle
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
b) The margin between the compressor working line and the surge line
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
a) 18:1
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
a) to maintain the velocity of the air under rising pressure
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
a) remains constant irrespective of height
