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M15 > M15.04 Compressors > Flashcards

M15.04 Compressors Flashcards

1
Q

What two ways can engines compress air?

A

. Decrease volume in a cylinder by a piston
. Bernoulli’s principle

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2
Q

What are two main components of a compressor?

A

Rotors and stators

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3
Q

What does each rotor have on it??

A

Rotor blades mounted on them

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4
Q

What do rotor blades do?

A

Suck in air and push it to the outlet side increasing velocity

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5
Q

What do stators have?

A

. Stator blades/ vanes
. They are fixed

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6
Q

What do stators do??

A

Guide and slow airflow to increase static pressure

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7
Q

The combination of rotors and stators is called??

A

Compressor stage

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8
Q

What part of the compressor stage always comes first?

A

Rotors

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9
Q

What are IGVs?

A

Inlet guide vanes

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10
Q

Where are IGVs positions?

A

In front of compressor stage

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11
Q

What is the purpose of IGVs?

A

Improve the airflow into the first compressor stage

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12
Q

Are IGVs fixed or movable?

A

Either

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13
Q

Where are stator vanes in the fan duct called?

A

Outlet guide vanes - OGVs

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14
Q

What is the purpose of OGVs?

A

Improve the airflow into fan nozzles (last stator)

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15
Q

What are they two main parts of the compressor?

A

. Compressor inlet case
. Compressor outlet case

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16
Q

What is the purpose of the compressor cases?

A

. Provide support
. Straighten the airflow into and out of the compressor

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17
Q

What are the two types of compressors??

A

. Axial flow compressor
. Centrifugal flow compressor

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18
Q

Where are centrifugal flow compressors used?

A

In small gas turbine engines - APU

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19
Q

What are the main components of the centrifugal flow compressor??

A

. The impeller (rotor)
. The diffuser ( stator)
. Compressor manifold

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20
Q

What is the pressure ratio for a centrifugal flow compressor?

A

5:1

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21
Q

What no. Stages have found to be efficient in centrifugal flow compressors?

A

2

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22
Q

What type of impellers are used in centrifugal flow compressors?

A

Single or double

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23
Q

What is the advantage of a double impeller on centrifugal compressor?

A

Gives a higher airflow, saves weight but doesn’t give higher pressure

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24
Q

What is a double impeller centrifugal compressor also known as?

A

Double face compressor

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25
Q

On an axial flow compressor where does the airflow flow?

A

Along the horizontal axis of the compressor

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26
Q

What are the channels between the rotors blades called?

A

Diffusers

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27
Q

What is the pressure ratio of each axial compressor stage?

A

1.3:1

28
Q

As pressure increase what also increases?

A

Density

29
Q

Why does compressor cross section gradually decrease on axial compressor? (Convergent)

A

Helps to keep the airflow velocity constant

30
Q

The achievable total pressure is lower for what type of compressors??

A

. Less total pressure for a centrifugal compressor
. More total pressure for an axial compressor

31
Q

What are both compressors sensitive too?

A

Changes in airflow

32
Q

Why are compressors sensitive to changes in airflow??

A

Because engine compressors only have one optimum operating condition for a given pressure, ratio, speed and airflow - THIS IS CALLED DESIGN POINT

33
Q

At the deign point, what occurs??

A

The airflow and rotational speed are perfectly matched

34
Q

When is the airflow into the rotor smooth??

A

As long as angle of attack to the rotor blades is small

35
Q

The shape of the rotor blades determines what on an axial compressor?

A

The direction of the airflow

36
Q

What is the job of the stator vanes on an axial compressor?

A

Decelerate the airflow and guide it to the next rotor stage
- only happens at one optimum compressor speed (design point)

37
Q

What is compressor stall??

A

Airflow separation from the compressor aerofoil/ blades

38
Q

What can compressor stall be caused by?

A

. Slowed, stopped or reversed airflow
. Coupled with higher angle of attack

39
Q

What is a compressor surge??

A

A very serve form of compressor stall

40
Q

What causes compressor surge?

A

Due to reverse airflow

41
Q

What engines can compressor surge occur on?

A

All engines, FWD or AFT compressor stages
(AFT is worse)

42
Q

When a compressor surge happens, what else is coupled with it?

A

. Heavy vibrations
. Loud banging noise
. ( thrust decrease, engine speed fluctuate, exhaust gas increases)

43
Q

What are a few reasons for compressor stall/surge?

A

. Dents or ice
. Damaged rotor or stator blades
. Dirty blades
. Damaged combustion
. Damaged turbine

44
Q

What are the two operational reasons for compressor stall/ surge??

A

. If speed is too far below design speed
. Incorrect acceleration or deceleration

45
Q

What 3 methods can be used to prevent stall/ surge??

A

. Use compressor bleed valve
. Use dual or triple spool rotors instead of single
. Use modern variable compressor stator vanes

46
Q

Where are compressor bleed valves found??

A

Found in the mod section and sometimes aft section of engine compressor

47
Q

When are the compressor bleed valves open?

A

Open at low engine speed, in order to allow excessive airflow from fwd staged to escape overboard

48
Q

What is abbreviation for LP compressor on a dual spool engine?

A

N1

49
Q

What is abbreviation for HP compressor on a dual spool engine?

A

N2

50
Q

What is each compressor rotor driven by in a dual spool engine?

A

Separate turbine

51
Q

What’s the most effective way to prevent compressor stall?

A

Variable stator vanes

52
Q

Where are the variable stator vanes found?

A

Fwd stages of HP compressor

53
Q

What’s the main disadvantage of the variable stator vane?

A

Very complicated control system

54
Q

What is the spinner cone also known as?

A

. Compressor inlet cone
. Nose cone

55
Q

What is the purpose of the spinner cone?

A

Creates a smooth aerodynamic fairing at the engine inlet

56
Q

What two shapes can the spinner cone be and why?

A

. Curved front
. Sharp tip
. To minimise ice build up

57
Q

What else do spinners have attached to the mounting bolts if needed?

A

Balance weights

58
Q

What is the fan rotor disc made out of?

A

Very large disc made of titanium alloy

59
Q

What fitting is used for fan rotor disc??

A

Dovetail fitting

60
Q

What does the fan rotor disc help with?

A

Supports the fan blades

61
Q

What are fan blades held in place by?

A

. Blade retainers
. On some engines bolts or cylindrical pins

62
Q

What two types of stresses do rotor blades experience?

A

. Centrifugal forces
. Air loads

63
Q

What do shrouds on fan blades ensure?

A

That blade deflection is within limits when experiencing heavy loads

64
Q

What do shrouds do that is special to dampen blade flutter?

A

Covered in a special coating which means they can slide easily in each other

Therefore, coverts the energy of the fluttering blade into friction, which dampens the flutter motion

65
Q

What are a few advantages of a wide chord fan blade?

A

. More efficient than a conventional blade
. Very flexible
. Can withstand FOD better

66
Q

What is another name for a low pressure compressor module??

A

Booster module

67
Q

Pg 65

A

M15 (10 decks)

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