15.6

Question 1

What does the turbine transform

Answer 1

Part of the kinetic (velocity) energy of exhaust gases into mechanical energy to drive gas generator compressors and accessories

Question 2

Purpose of gas generator turbine

Answer 2

Absorb 60-70% of total pressure energy from the exhaust gases

Question 3

Where is the turbine located

Answer 3

Aft or downstream of the combustion chamber

Directly behind gas chamber outlet

Question 4

Turbine main components

Answer 4

Stationary vanes - turbine nozzle guide vanes

Rotor blades on a turbine disk

Question 5

Radial flow stage ?

Answer 5

Single stage used on APU

Question 6

Radial flow disadvantage

Answer 6

Small airflows and less efficient due to high aerodynamic losses

Question 7

Where are axial flow turbines used

Answer 7

Modern GTE

Question 8

Advantage of axial flow turbine

Answer 8

Very high airflow required to create a high thrust

Question 9

Turbine stage

Answer 9

Stator and rotor

(Stator first)

Question 10

How many stages can an axial flow turbine have

Answer 10

Any number of

Question 11

What does the turbine convert

Answer 11

Gas energy from combustion chamber into torque

Question 12

After the combustion chamber what’s the first part the gas flows through

Answer 12

Stationary turbine nozzle guide vanes Rotor blades

Question 13

How is the gas flow in the combustion chamber accelerated

Answer 13

Convergent shape duct between nozzle guide vanes Rotor blades

Question 14

What is an impulse turbine

Answer 14

Turbine that only rotates due to impact of gas flow

Question 15

3 types of turbine blade

Answer 15

Impulse

Reaction

Reaction - impulse

Question 16

In an impulse turbine where does the total pressure drop occur

Answer 16

Fixed nozzle guide vanes because of their convergent shape

Question 17

In a impulse configuration what is pressure energy converted to

Answer 17

All pressure energy converted into kinetic energy

Question 18

What is a reaction type configuration designed to do

Answer 18

Alter gas flow direction without changing the pressure

Question 19

What turbine combination do GTE use

Answer 19

Reaction - impulse

Question 20

What forces are acting on a reaction turbine

Answer 20

Both impulse and reaction forces that acts in the plane of rotation to drive the turbine

Question 21

What do impulse turbines require

Answer 21

High - velocity gas to obtain the maximum rate of momentum change

Question 22

How does a reaction turbine cause its rate of momentum to change

Answer 22

By nozzling action of the rotor blade

Question 23

What does a uneven workload cause if the blade

Answer 23

Gases to exit from the blade at different velocities and pressures

Question 24

What type of cast are most blades

Answer 24

Precision

Question 25

Why do we cast as single crystal

Answer 25

Gives blades better strength and heat properties

Question 26

How do we keep turbine blades and inlet nozzles cooler

Answer 26

Using heat barrier coatings like ceramic coatings Airflow cooling

Question 27

What effect does keeping inlet nozzles cooler have

Answer 27

Increase efficiency of the engine

Question 28

Advantage of shrouded turbine blades

Answer 28

Improves efficiency and vibration characteristics Lighter stage weights

Question 29

Disadvantage of shrouded turbine blades

Answer 29

Limits turbine speed and requires more blades

Question 30

Why do we need additional turbine stages

Answer 30

Single turbine wheel cannot absorb enough power from exhaust gases to drive the components

Question 31

What does the rotor element of a turbine section consist of

Answer 31

Shaft and wheel

Question 32

Why do we control engine speed and temperature

Answer 32

To keep turbine within operations limits due to high centrifugal loads and temperatures on it

Question 33

How is a turbine wheel balanced

Answer 33

Dynamically

Question 34

What is the disc attached to

Answer 34

Main power-transmitting shaft of the engine

Question 35

What is the purpose of grooves/notches in the rim of the disk

Answer 35

Allow attachment of the turbine blades and space for thermal expansion

Question 36

What material is turbine shaft

Answer 36

Alloy steel that can absorb high torque loads

Question 37

How do you cool the disk rim

Answer 37

Bleeding cooling air back onto the face of the disk

Question 38

Most common method of connecting shaft to turbine disk

Answer 38

Bolting

Question 39

How is the turbine shaft attached to compressor rotor hub

Answer 39

Spline cut on the forward end of the shaft

Question 40

What does a spline it into

Answer 40

Coupling device between compressor and turbine shafts

Question 41

What do we use if a coupling is not used

Answer 41

Splined end of the turbine shaft may fit into a splined recess in the compressor rotor hub

Question 42

Where is the splined coupling arrangement used

Answer 42

Centrifugal compressor engines

Question 43

Most common way to attach turbine blades

Answer 43

Fir tree design

Question 44

Methods of retaining blades

Answer 44

Peening , welding , lock tabs and riveting

Question 45

What is a notch filled with

Answer 45

Disc material

Question 46

Why is the tang bent

Answer 46

Secure blade in the disc

Question 47

What does using the Blade root as a stop do

Answer 47

Made on one end so the blade can only be inserted and removed in one direction

Question 48

2 parts of turbine assembly

Answer 48

Stator - nozzle and inlet guide vanes Turbine blades (rotor)

Question 49

Stator 3 different names

Answer 49

Turbine inlet nozzle vanes Turbine inlet guide vanes Nozzle diaphragm

Question 50

Where is the turbine inlet nozzle vane located

Answer 50

Aft of the combustion chambers and immediately forward of the turbine wheel

Question 51

Where are turbine inlet nozzle assembled

Answer 51

Between outer and inner shrouds on rings

Question 52

Where do vanes fit

Answer 52

Contoured slot in the shrouds

Question 53

How can we fit vanes into inner and outer shrouds

Answer 53

Weld or river them into position

Question 54

Why is the shroud ring cut into segments

Answer 54

To allow for thermal expansion

Question 55

What’s a structural inspection technique

Answer 55

Dye penetrant

Question 56

How can we get rid of putting in blades

Answer 56

Stoning and polishing

Question 57

How do stress rupture cracks from

Answer 57

At aright angle to the edge length

Question 58

How does deformation due to over temperature appear

Answer 58

Waviness

Question 59

Length of visible cracks

Answer 59

1/16th inch upwards

Question 60

What happens if cracks or deformation occurs on the leading edge of the first stage turbine blade

Answer 60

Over temperature condition must be suspected

Question 61

What is creep

Answer 61

Slow structural deformation on a molecular level

Question 62

How does creep occur

Answer 62

Prolog exposure to high stresses and high temperatures

Question 63

What does scoring on the turbine case suggest

Answer 63

Length of blades out of tolerance