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BGT > Hot section πŸ”₯ > Flashcards

Hot section πŸ”₯ Flashcards

1
Q

What does a swirl chamber do

A

Using holes or slots it converts pressure energy to kinetic energy

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2
Q

What speed does air leaving the compressor travel at

A

150m/s

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3
Q

What does flame stability rely on

A

Fuel air ratio and airflow speed

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4
Q

What percentage of air goes into the combustion chamber

A

20%. Of this 20%, 12% goes over swirl vanes and mixes with atomised fuel. The remaining 8% flows through a perforated flare and stabilises the flame

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5
Q

What does primary air do

A

Provides the high temperature for rapid combustion

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6
Q

What does secondary air do

A

It consists of 20% of the non bypass air and is Introduced to the combustion in stages to prevent a cold flame and slows the air down and Completes the combustion

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7
Q

What is tertiary air for

A

It is the remaining 60% of non bypass airflow and cools the air prior to entering the turbine section

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8
Q

What are the four types of combustion chambers

A

Multiple can
Can annular/turbo annular
Annular
Reverse flow annular

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9
Q

Multiple can combustion characteristics

A

Number of cans around engine interconnected to equalise pressure
Individual cans can be replaced
Strong

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10
Q

Can annular/tubo annular characteristics

A

Number of flame tubes fitted inside an air casing
Individual cans can be replaced
Easy to manufacture

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11
Q

Annular combustion characteristics

A

A single flame tube
75% smaller than other types and requires 15% less cooling
Even gas distribution
More efficient as lighter and less pressure loss
Easy to manufacture

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12
Q

Reverse flow annular combustion characteristics

A

Makes engines able to be smaller due to reversing airflow
Popular in turbo shafts and props
Usable on smaller aircraft

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13
Q

Purpose of the turbine

A

Extracts energy from the high pressure and high temperature gases from the combustion chamber.this energy turns the compressor and engine driven accessories

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14
Q

What are the two types of turbine

A

Axial flow turbine
Free power turbine

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15
Q

Axial flow turbine properties

A

It is turned on by the hot gases from the combustion chamber and is physically connected to the compressor

Fitted on single, dual and triple spooled engines

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16
Q

Free power turbine properties

A

Not physically connected to the compressor

17
Q

Why must compressors and turbines be matched

A

To obtain max efficiency and performance of the engine

18
Q

What is the casing or case assembly

A

A case enclosing the turbine, stator and rotor which is connected to the combustion at the front and the exhaust nozzle at the back end

19
Q

What are NGVs

A

Nozzle guide vanes
Stationary vanes in front of first turbine wheel presenting air at the most efficient angle of attack
Allow expansion and acceleration of hot gases
Hollow for cooling
Have shrouds fitted at the top and bottom of the vane

20
Q

ITT Meaning

A

Interstage turbine temperature

21
Q

TIT meaning

A

Turbine inlet temperature

22
Q

EGT meaning

A

Exhaust gas temperature

23
Q

Turbine wheel properties

A

It’s the rotating part of the turbine along with the turbine shaft
Each wheel increases in diameter and blade size towards the exhaust
Stator between each wheel

24
Q

In a turbine what is a stage

A

A turbine wheel and a stator pairing

25
Q

Turbine blade material properties

A

Strong
Thermal shock resistant
Creep resistant
Economic manufacture
Corrosion resistant

26
Q

Two ways a turbine blade is connected to the turbine wheel

A

By a fir tree root. It’s loose when stationary then held in place by centrifugal forces

BLISK - bonding the blades to the disk which is 8% more efficient than the fir tree method

27
Q

How is and impulse reaction blade configured

A

The blade root is an impulse blade and the blade tip is a reaction blade.
This is the most common type of turbine blade

28
Q

Three types of turbine blades

A

Impulse -pressure drop in convergent NGVs
Reaction- pressure drop between rotor blades
Impulse reaction -compromise between the two

29
Q

TET meaning

A

Turbine entry temperature

30
Q

What is the main limiting factor for turbines

A

TET turbine entry temperature

31
Q

Turbine limiting factors

A

TET
Metal fatigue
Corrosion
Oxidisation
Abrasion

32
Q

What is Primary blade creep

A

Creeps rapidly over a short time then the rate decreases

33
Q

What is secondary creep

A

Small and steady creep over time

34
Q

What is tertiary creep

A

Rate accelerates over time until the material breaks

35
Q

Parts of the exhaust section

A

Exhaust unit
Jet pipe
Propelling nozzle

36
Q

Low bypass engine exhausts have hot and cold airstreams combined using a

A

Mixer unit

37
Q

High bypass engines exhaust the hot (combusted) and cold (bypass) airstreams through

A

Seperate coaxial nozzles or an intergrated nozzle

BGT (10 decks)

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