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M15 > 15.04 > Flashcards

15.04 Flashcards

1
Q

What are the two ways you can compress air in an engine?

A

. Decrease the volume in a cylinder
. Make use of Bernoulli’s principe

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2
Q

What are the two main compressor components?

A

Rotor and stator

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3
Q

What does the rotor do?

A

Increase airflow energy

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4
Q

What does the stator do?

A

Guide the airflow

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5
Q

What are the set of stators in front a compressor stage called?

A

Inlet guide vanes

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6
Q

What are the stators called in the fan duct?

A

Outlet guide vanes

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7
Q

Where are centrifugal flow compressors usually found?

A

Small gas turbine engines such as APU

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8
Q

What is the pressure ratio of centrifugal flow compressors?

A

5:1

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9
Q

What is it called when two impellers are mounted face to face?

A

Double face compressor

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10
Q

What are some advantages of double face compressors?

A

Air can enter from front and back, higher airflow, saves weight

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11
Q

In an axial flow compressor what do the rotors do?

A

Increase velocity of the air but also slow it down, and increase static pressure

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12
Q

Why do we taper axial flow compressors?

A

Maintain velocity

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13
Q

The airflow in the axial compressor is smooth as long as?

A

The angle of attack on the rotor and stator vanes is small

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14
Q

What is airflow separation also called?

A

Compressor stall

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15
Q

What does compressor stall cause the airflow to do?

A

Airflow stops and slows down and sometimes reverses

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16
Q

What is a severe form of compressor stall?

A

Compressor surge

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17
Q

Where can compressor surge happen?

A

Fwd or aft compressor stage

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18
Q

What happens at compressor surge in the aft compressor?

A

Airflow decreases rapidly and reverses

19
Q

What are some reasons for stall and surge in the compressor?

A

Dents or ice, damaged rotor blades, dirty blades, damaged compressor, damaged turbine

20
Q

How can the compressor stall?

A

Engine is far below designed speed, incorrect acceleration or deceleration

21
Q

What are the methods to avoid compressor stall and surge?

A

Compressor bleed valves, use dual or triple spool instead of single, variable compressor stator vanes

22
Q

When are compressor bleed valves opened?

A

Low engine speeds

23
Q

Each compressor rotor is driven by a separate?

A

Turbine

24
Q

What is the most effective method to prevent stall?

A

Variable stator vanes

25
Q

What does the spinner comb create?

A

Smooth aerodynamic fairing at engine inlet

26
Q

What is the fan rotor disc made from?

A

Titanium alloy

27
Q

What type of fitting is used on most aircraft?

A

Dovetail fitting

28
Q

What is a loose fit necessary on engine parts?

A

Allow for sudden forces or torques

29
Q

What forces act on rotor blades?

A

Centrifugal force and air loads

30
Q

What does the shroud help the fan blade do?

A

Keeps deflection within safe limits

31
Q

What can a wide chord blade withstand?

A

Foreign object damage because of its flexibility

32
Q

On a turbofan engine the fan case has?

A

One or more ring elements

33
Q

What do linings provide in the fan case?

A

Smooth surface for airflow

34
Q

What do the holes on the fan case reduce?

A

Noise

35
Q

When does unbalance occur on the fan rotor?

A

Material is removed from the blade

36
Q

What is the best method when replacing a fan blade?

A

New blade with almost equal weight to the old one

37
Q

What are balance weights used for on blades?

A

Compensate for imbalances

38
Q

What seal do knife edges create?

A

Labyrinth seal

39
Q

Each HP compressor always has a ….. seal

A

CDP

40
Q

Why do inner ends of vane segments have an inner platform?

A

Reduce vibrations

41
Q

Compressors with high compression ratios have?

A

Variable stator vanes

42
Q

What does the HP compressor source?

A

Pressurised air for pneumatic system

43
Q

What is bleed air supplied through?

A

Hollow stator vanes

M15 (17 decks)

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