15 Gas Turbines Compressors – LMS

📄 Detailed Notes ⚡ Cheat Sheet

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📄 Notes ⚡ Cheat Sheet

Q1. A gas turbine engine turbine section may employ active clearance control:

as a method of attaching the stators and rotors to the hub of the disc

to provide enhanced clearances between the blade tips and the casing

in order to reduce "creep" in the blades

in order to cool the disc

Q2. The blades in an axial flow compressor decrease in size from the:

root to the tip in order to increase tip clearance.

high pressure to the low pressure stages in order to allow for expansion at increased velocity.

low pressure to the high pressure stages in an attempt to sustain axial velocity.

root to the tip in order to maintain a constant angle of attack.

Q3. One stage of an axial compressor comprises:

a row of rotor blades followed by a row of inlet guide vanes.

a row of inlet guide vanes followed by a row of rotor blades.

a row of rotor blades followed by a row of stator vanes.

inlet guide vanes followed by a row of rotor blades and a row of stator vanes.

Q4. The axial compressor of a gas turbine engine usually has more stages than its driving turbine because:

turbine speed is much higher than compressor speed.

the power output of a turbine stage is higher than the power consumption of a compressor stage.

the compressor consumes much more power than the turbine.

bleed air is taken from the compressor.

Q5. The characteristics of an axial compressor are:1 – a low pressure ratio by stage.2 – a high pressure ratio by stage.3 – the possibility of compressing a large mass airflow.4 – the inability of compressing a large mass airflow. The combination that regroups all of the correct statements is:

1 and 4 only.

2 and 4 only.

2 and 3 only.

1 and 3 only.

Q6. In the annex, an axial compressor stage is represented by:

figure 2

figure 4

figure 3

figure 1

Q7. In the axial flow compressor of a turbo-jet engine, the flow duct is tapered. Its shape is calculated so as to:

maintain a constant axial speed in cruising flight

reduce the axial speed in cruising flight

maintain a constant axial speed whatever the engine rating

reduce the axial speed, whatever the engine rating

Q8. Compressor stall in a gas turbine engine:

is unlikely to occur in a compressor with many stages.

only occurs during engine start-up.

does not occur with well-designed compressor blades.

can be caused by an axial airflow velocity that is low relative to the rotor speed.

Q9. The characteristics of a centrifugal compressor are:1 – a high pressure ratio by stage.2 – a large diameter.3 – a low pressure ratio by stage.4 – a small diameter. The combination containing all of the correct statements is:

2 and 3 only

3 and 4 only

1 and 4 only

1 and 2 only

Q10. The disadvantages of axial flow compressors compared to centrifugal flow compressors are:1 – more expensive to manufacture2 – lower airflow3 -greater vulnerability to foreign object damage4 – lower pressure ratio The combination which regroups all of the correct answers is:

2.Apr

2 – 3

1.Feb

1.Mar

Q11. The compressor pressure ratio of an axial flow compressor is primarily determined by the:

rotor diameter.

compressor inlet pressure design value.

compressor inlet temperature design value.

number of stages.

Q12. An axial compressor, when operating below its design speed, has:

a tendency to stall in the rear stages

a tendency to stall in the centre stages

no tendency to stall

a tendency to stall in the front stages

Q13. Using compressor bleed air to power systems:

decreases aircraft performance

increases aircraft performance

is limited to the phases of take-off and landing

has no influence on aircraft performance

Q14. The rotor blades of an axial compressor of a gas turbine engine are often mounted on a disk or drum using a ‘loose fit’ because this:

facilitates easy assembly and removal.

limits damage due to creep.

limits FOD damage.

limits damage to the blades due to vibration.

Q15. A stage in an axial compressor:

is made of a rotor disc followed by a row of stator blades

has a compression ratio in the order of 2.1

has a compression ration in the order of 0.8

is made of row of stator blades followed by a rotor disc

Q16. In a gas turbine engine, compressor blades, which are not rigidly fixed in position when the engine is stationary, take up a rigid position when the engine is running due to:

oil pressure

thermal expansion

the resultant of aerodynamic and centrifugal forces

blade creep

Q17. The compressor blades in a rotating gas turbine engine are held in position by:

abradable seals and aerodynamic forces

the mountings and the resultant of aerodynamic and centrifugal forces

a centrifugal latch

the mountings and thermal expansion only

Q18. In a compressor stage of a jet engine, the sequence is:

stator - stator – rotor

rotor - rotor - stator

rotor - stator

stator - rotor

Q19. A diffuser in a gas turbine engine is a device in which the:

velocity, pressure and temperature rise.

velocity rises and pressure falls.

pressure rises at a constant velocity.

pressure rises and velocity falls.

Q20. The diffuser in a centrifugal compressor is a device in which the:

pressure rises and velocity falls

velocity, pressure and temperature rise

pressure rises at a constant velocity

velocity rises and pressure falls

Q21. The primary function of the diffuser, located between the compressor and the combustion chamber of a gas turbine engine is to:

Decrease the flow velocity

Increase the temperature of the compresses air

Convert kinetic energy into mechanical energy

Increase total pressure

Q22. The primary function of the diffuser, located between the compressor and the combustion chamber, of a gas turbine engine is to:

convert kinetic energy into mechanical energy.

decrease the flow velocity.

increase the temperature of the compressed air.

increase total pressure.

Q23. About a twin spool compressor:

The low pressure spool runs at a very high rpm, thus preventing the onset of compressor stall.

The low pressure spool (N1) runs at a lower rpm than the high pressure (N2) spool.

Both spools run at the same rpm.

When operating at very high rpm's, the later stages within the high pressure spool will have a large negative angle of attack.

Q24. About a twinspool compressor:

Both spools will run at the same RPM

When operating at very high RPM, the later stages within the high pressure spool will have a large negative angle of attack

The low pressure spools runs at a lower RPM than the high pressure spool

The low pressure spool runs at a very high RPM, thus preventing the onset of compressor stall

Q25. The following problems may occur when starting a twin-spool turbofan engine:

no N1 rotation, although N2 may accelerate normally.

a hung (abortive) start with no light-up indication after 'fuel-on' selection.

no N2 rotation, although N1 may accelerate normally.

a hung (abortive) start with fuel flow indication zero after 'fuel-on' selection.

Q26. Some gas turbine engines have multiple stages in the HP and LP turbines:

to reduce noise in the propelling nozzle.

to help stabilise the pressure between the compressor and the turbine.

because one stage does not generate sufficient shaft power.

to facilitate balancing of Turbine Assembly.

Q27. A stage in an axial compressor:

consists of a rotor disc followed by a ring of stator blades

has a compression ratio in the order of 2.1

has a compression ration in the order of 0.8

consists of a ring of stator blades followed by a rotor disc

Q28. In addition to providing ‘customer’ bleed for aeroplane systems, air may be bled from compressors of a turbofan engine to increase stall margin:

at low rotor speed.

and prevent stall at high rotor speed.

and recover from stall at high rotor speed.

at high rotor speed.

Q29. Compressor stall is due to:

an inadequate fuel flow.

an excessively high axial velocity.

an excessively low angle of attack of the rotor blades.

an excessively high angle of attack of the rotor blades.

Q30. In a compressor stage, if the axial air velocity increases more than the rotor blade velocity the:

stall margin increases.

pressure ratio will be too high.

relative air velocity becomes supersonic.

stall margin decreases.

Q31. Compressor surge may be controlled by means of:

bleed valves.

fixed inlet guide vanes.

a variable metering orifice.

a pressure drop control orifice.

Q32. Severe compressor stall can be indicated amongst others by:

a rise in TGT and an increase in fuel flow

a decrease in TGT and a change in vibration level

an increase in engine pressure ratio (EPR) and a decrease in TGT and fuel flow

a rise in turbine gas temperature (TGT) and a change in vibration level

Q33. Severe compressor stall can be observed amongst others by:

a decrease in TGT and a change in vibration level

a rise in turbine gas temperature (TGT) and a change in vibration level

an increase in engine pressure ratio (EPR) and a decrease in TGT and fuel flow

a rise in TGT and an increase in fuel flow

Q34. Severe compressor stall can be observed amongst others by:

a decrease in TGT and a increase in vibration level.

a rise in turbine gas temperature (TGT) and a increase in vibration level.

a rise in TGT and an increase in fuel flow.

an increase in engine pressure ratio (EPR) and a decrease in TGT and fuel flow.

Q35. Below its design speed an axial compressor:

has a tendency to stall in the centre stages

has a tendency to stall in the front stages

has no tendency to stall

has a tendency to stall in the rear stages

Q36. Which of these statements about compressor stall are correct or incorrect?I. A compressor stall is most likely to occur in a compressor designed for a high pressure ratio operating at low RPM.II. A compressor stall is most likely to occur when the air flow stagnates in the rear stages of the compressor.

I is incorrect, II is correct.

I is incorrect, II is incorrect.

I is correct, II is incorrect.

I is correct, II is correct.

Q37. Which of these statements about compressor stall are correct or incorrect?I. A compressor stall is most likely to occur in a compressor designed for a high pressure ratio operating at high RPM.II. A compressor stall is most likely to occur when the air flow stagnates in the rear stages of the compressor.

I is correct, II is correct.

I is incorrect, II is incorrect.

I is correct, II is incorrect.

I is incorrect, II is correct.

Q38. Which of these statements about compressor stall are correct or incorrect?I. A compressor stall is most likely to occur in a compressor designed for a high pressure ratio operating at high RPM.II. A compressor stall is most likely to occur when the air flow stagnates in the front stages of the compressor.

I is correct, II is incorrect.

I is incorrect, II is correct.

I is correct, II is correct.

I is incorrect, II is incorrect.

Q39. When a gas turbine engine accelerates from idle to take-off thrust and the compressor rpm is too high in comparison with the Air Inletsss velocity, this may result in:

supersonic airflow at the compressor blade trailing edges.

a compressor blade airflow angle of attack that is too small.

a compressor stall.

stagnation.

Q40. Which of the following statements regarding variable inlet guide vanes (VIGVs) and variable stator vanes (VSVs) on a high-bypass engines is correct?

VIGVs prevent LP compressor stall and VSVs prevent HP compressor stall.

VIGVs are located in the front of the fan and control both fan and compressor air flow. VSVs are used in the compressor only and are used to increase pressure ratio.

If VIGVs move towards the open position, VSVs move towards the closed position.

VIGVs are located at the front of the HP compressor and, together with the VSVs, control compressor airflow.

Q41. One advantage of having three instead of two spools in some high-bypass turbofan engine is that:

there is a lower fuel consumption and more thrust due to higher overall pressure ratio.

fewer variable stator vanes and variable inlet guide vanes are required to prevent compressor stall at low rotor speeds.

fewer variable stator vanes and variable inlet guide vanes are required to prevent compressor stall at high rotor speeds.

there is a lower fuel consumption due to a higher overall pressure ratio.

Q42. One of the purposes of compressor bleed valves is to:

increase the airflow across the rear compressor stages, whilst that across the early stages is decreased

limit the acceleration period of the engine

decrease the airflow across the rear compressor stages, whilst that across the early stages is increased

decrease the load on the compressor when the engine is approaching maximum rpm

Q43. The purpose of a variable bypass valve, fitted between the LP and HP compressor of an axial flow compressor, is to:

control the acceleration of the engine.

prevent stall in the LP compressor.

enable to start the engine with an external air supply.

prevent the engine from an overspeed.

Q44. The primary purpose of the bleed valves fitted to axial flow compressors is to :

spill compressor air should the engine overspeed thus controlling the speed

reduce the likelihood of compressor stall

enable an external air supply to spin up the compressor for engine starting

control the acceleration time of the engine

Q45. The purpose of a compressor bleed valve is to prevent surging:

of the first compressor stages

with altitude

generated by foreign object ingestion

at low compressor rpm

Q46. The compressor surge effect during acceleration is prevented by the:

variable setting type nozzle guide vanes

inlet guide vanes

surge bleed valves

Fuel Control Unit (F.C.U.)

Q47. The purpose of variable by-pass valves in a high bypass turbofan engine between the LP compressor and the HP compressor (HPC) is to:

prevent HPC stall during engine start.

provide sufficient air to the HPC during engine start.

prevent fan surge at high rotor speeds (high rpm).

prevent fan stall and LP compressor stall during engine start and low rotor speeds.

Q48. The air flow passages between adjacent axial compressor rotor blades are divergent, but the absolute exit velocity is higher than the absolute entry velocity of the rotor. This is because:

the gas expands between the blades.

it is a constant temperature process.

part of the compressor work delivered to the air is converted into kinetic energy.

the compressor rotational velocity slows down the air flow.

Q49. After air has passed through the compressor of a gas turbine engine the:

pressure will be the same as the inlet pressure

temperature will be higher than the inlet temperature

velocity will be the same as the inlet velocity

velocity will be higher than the inlet velocity

Q50. The station numbers before and after the HP compressor are:

2.5 and 3

2 and 2.5

5 and 6

3 and 4

Q51. A twin spool gas turbine engine is one in which the:

LP turbine drives both the LP compressor and the HP compressor.

LP turbine drives the LP compressor and the HP turbine drives the HP compressor.

LP compressor drives the HP compressor.

turbines are free to rotate at speeds that differ from their associated compressors.

Q52. The kind of compressor normally used as a supercharger is:

a hybrid compressor

an axial compressor

a piston compressor

a radial compressor

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Results

Q1. A gas turbine engine turbine section may employ active clearance control:

Q2. The blades in an axial flow compressor decrease in size from the:

Q3. One stage of an axial compressor comprises:

Q4. The axial compressor of a gas turbine engine usually has more stages than its driving turbine because:

Q6. In the annex, an axial compressor stage is represented by:

Q7. In the axial flow compressor of a turbo-jet engine, the flow duct is tapered. Its shape is calculated so as to:

Q8. Compressor stall in a gas turbine engine:

Q9. The characteristics of a centrifugal compressor are:1 – a high pressure ratio by stage.2 – a large diameter.3 – a low pressure ratio by stage.4 – a small diameter. The combination containing all of the correct statements is:

Q10. The disadvantages of axial flow compressors compared to centrifugal flow compressors are:1 – more expensive to manufacture2 – lower airflow3 -greater vulnerability to foreign object damage4 – lower pressure ratio The combination which regroups all of the correct answers is:

Q11. The compressor pressure ratio of an axial flow compressor is primarily determined by the:

Q12. An axial compressor, when operating below its design speed, has:

Q13. Using compressor bleed air to power systems:

Q14. The rotor blades of an axial compressor of a gas turbine engine are often mounted on a disk or drum using a ‘loose fit’ because this:

Q15. A stage in an axial compressor:

Q16. In a gas turbine engine, compressor blades, which are not rigidly fixed in position when the engine is stationary, take up a rigid position when the engine is running due to:

Q17. The compressor blades in a rotating gas turbine engine are held in position by:

Q18. In a compressor stage of a jet engine, the sequence is:

Q19. A diffuser in a gas turbine engine is a device in which the:

Q20. The diffuser in a centrifugal compressor is a device in which the:

Q21. The primary function of the diffuser, located between the compressor and the combustion chamber of a gas turbine engine is to:

Q22. The primary function of the diffuser, located between the compressor and the combustion chamber, of a gas turbine engine is to:

Q23. About a twin spool compressor:

Q24. About a twinspool compressor:

Q25. The following problems may occur when starting a twin-spool turbofan engine:

Q26. Some gas turbine engines have multiple stages in the HP and LP turbines:

Q27. A stage in an axial compressor:

Q28. In addition to providing ‘customer’ bleed for aeroplane systems, air may be bled from compressors of a turbofan engine to increase stall margin:

Q29. Compressor stall is due to:

Q30. In a compressor stage, if the axial air velocity increases more than the rotor blade velocity the:

Q31. Compressor surge may be controlled by means of:

Q32. Severe compressor stall can be indicated amongst others by:

Q33. Severe compressor stall can be observed amongst others by:

Q34. Severe compressor stall can be observed amongst others by:

Q35. Below its design speed an axial compressor:

Q39. When a gas turbine engine accelerates from idle to take-off thrust and the compressor rpm is too high in comparison with the Air Inletsss velocity, this may result in:

Q40. Which of the following statements regarding variable inlet guide vanes (VIGVs) and variable stator vanes (VSVs) on a high-bypass engines is correct?

Q41. One advantage of having three instead of two spools in some high-bypass turbofan engine is that:

Q42. One of the purposes of compressor bleed valves is to:

Q43. The purpose of a variable bypass valve, fitted between the LP and HP compressor of an axial flow compressor, is to:

Q44. The primary purpose of the bleed valves fitted to axial flow compressors is to :

Q45. The purpose of a compressor bleed valve is to prevent surging:

Q46. The compressor surge effect during acceleration is prevented by the:

Q47. The purpose of variable by-pass valves in a high bypass turbofan engine between the LP compressor and the HP compressor (HPC) is to:

Q48. The air flow passages between adjacent axial compressor rotor blades are divergent, but the absolute exit velocity is higher than the absolute entry velocity of the rotor. This is because:

Q49. After air has passed through the compressor of a gas turbine engine the:

Q50. The station numbers before and after the HP compressor are:

Q51. A twin spool gas turbine engine is one in which the:

Q52. The kind of compressor normally used as a supercharger is:

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