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M15 New > 15.4 > Flashcards

15.4 Flashcards

1
Q

Primary function of a compressor

A

Supply right amount of air combustion chamber needs at the right pressure

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2
Q

Secondary function of compressor

A

Supply air to systems that need bleed air

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3
Q

Where are bleed ports located

A

Depends on pressure or temperature of the system required

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4
Q

What is a compressor stage

A

Combination of rotor and stator

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5
Q

What is the first part of the compressor stage

A

Rotor

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6
Q

What does a rotor do

A

Such in air and push it to the outlet side of the rotor which increases energy of the airflow

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7
Q

What does a stator do

A

Guide of slow airflow to cause an increase in pressure

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8
Q

What are stator blades called

A

Stator vanes

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9
Q

What are stator vanes at the front of the compressor stage

A

Inlet guide vanes that improve airflow into the first compressor stage

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10
Q

What are the stator vanes in the fan duct called

A

Outlet guide vanes that improve airflow into fan nozzle

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11
Q

What 3 parts does a compressor have

A

Impeller (rotor)

Diffuser(stator)

Compressor manifold

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12
Q

What is the high pressure rise per stage in a centrifugal compressor

A

8:1

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13
Q

What is a centrifugal impeller made of and why is it smoothed

A

Forged alluminum alloy

Smoothed for minimum flow restriction and turbulence

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14
Q

Which impeller entry is more complicated

A

Double - entry

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15
Q

Where are axial flow compressors found

A

Turbofan engines

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16
Q

Where are centrifugal compressors found

A

Turboprop and turbo shaft engines

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17
Q

In an axial flow compressor why does the diameter of the rotating drum gradually decrease

A

Maintain steady axial velocity as pressure and density of the air increases

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18
Q

What does a multi spool compressor consist of

A

Two or three drums of rotors

Each drum is driven by a separate turbine

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19
Q

Why is the compression ratio small

A

Amount of deflection and degree of deflection is low to minimise loss due to flow separation and stall

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20
Q

Why don’t we always add large number of stages to get a high compression rate

A

Optimising design to be most efficient becomes difficult

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21
Q

When do rotors run free of vibration

A

When Fan blades are opposite each other create identical centrifugal forces

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22
Q

What 3 parameters does fan blades depend on

A

Rotor speed

Blade mass

Distance of CoG of fan blade from rotational axis

23
Q

What is the moment weight

A

Product of Blade mass and Distance of CoG of fan blade from rotational axis

24
Q

Where is moment weight displayed

A

At the blade root

25
Q

What is moment weight given in

A

Gram inches

Cm.g

Ounce inches

26
Q

What numbers are at the blade root

A

Part number

Serial number

Moment weight

27
Q

What is the entire assembly of diffuser and manifold referred to as

A

Diffuser

28
Q

What is the best method to replace a blade

A

With a new one with as close moment weight as the old one

29
Q

What are balance weighs used for

A

When a new blades moment weight larger then specified from the manufacturer

30
Q

Where are balance weights installed

A

Fan disc or spinner cone

31
Q

What’s the second method of changing fan blades

A

Change a pair with similar moment weights

(The pair would be the damaged blade and the blade opposite it)

32
Q

How do we achieve smooth airflow

A

Having the correct relationship between inlet velocity and rotor speed

33
Q

What angle of attack do we need to ensure smooth airflow

A

AoA to the rotor blades is small

34
Q

What makes the AoA increase

A

Inlet air velocity decreases

35
Q

What is compressor stall

A

Airflow separation which causes air to slow down, stop or reverse direction

36
Q

What is compressor surge

A

Severe form of compressor stall

37
Q

Where stages can compressor surge occur

A

Forward and aft stages

38
Q

How is compressor stall and surge caused

A

Problems in engine operations or damaged engine components

39
Q

How can we achieve a high compression rate

A

Large number of stages

40
Q

3 methods to prevent stall and surge

A

Bleed valves

Dual or triple spool rotors

Variable compressor stator vanes

41
Q

Where are bleed valves found

A

Mid section or aft section of engine

42
Q

What do bleed valves do

A

Open at low engine speeds so excessive airflow can escape overboard

43
Q

What is n1 and n2

A

N1 - low pressure compressor

N2 - high pressure compressor (aft)

(Both driven by separate turbine)

44
Q

What’s the most effective method of preventing Stall

A

Variable stator vanes in the compressor

45
Q

Where are the variable inlet guide vanes and stator vanes found

A

Fwd stages of high pressure compressor

46
Q

Advantage of variable stator vanes

A

Optimum AoA on rotor blades for every engine speed

47
Q

Disadvantage of variable stator vanes

A

Very complicated control mechanism

48
Q

What is compression ratio

A

Volume of its combustion chamber for largest to smallest capacity

49
Q

Axial flow compressor pressure ratio

A

1:3:1

50
Q

How are fan blades numbered

A

Often in direction of rotation

51
Q

Stages in a centrifugal compressor limited to

A

2 stages

52
Q

What’s a disadvantage of centrifugal flow

A

Lots of twists and turns

53
Q

What’s the sequence of turbines and compressors in a triple spool engine

A

LPC - IPC - HPC ~> HPT - IPT - LPT

M15 New (18 decks)

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