15.6 Turbine Section

Question 1

What does the turbine section do?

Answer 1

Transforms kinetic energy to mechanical energy to drive the compressor and accessories.

Question 2

What is the purpose of a gas generator turbine?

Answer 2

To absorb 60 to 70% of total pressure energy.

Question 3

What are the 2 types of turbines used?

Answer 3

Radial flow and axial flow.

Question 4

What can be said about the stages of a radial flow turbine?

Answer 4

Always only single stage.

Question 5

Where is a radial flow turbine used?

Answer 5

On APUs.

Question 6

What are the negatives of a radial flow turbine?

Answer 6

Small airflow.
Less efficient.

Question 7

Where are axial flow turbines used?

Answer 7

On modern engines.

Question 8

What is the advantage of the axial flow turbine?

Answer 8

Allows very high airflow to create high thrust.

Question 9

What does a stage consist of in the turbine?

Answer 9

Nozzle guide vane (stator), then a rotor.

Question 10

What effect do nozzle guide vanes in the turbine have on velocity and pressure?

Answer 10

V increases.
P decreases.

Question 11

What effect do rotors in the turbine in the turbine heave on velocity and pressure?

Answer 11

V decreases.
P increase.

Question 12

How do turbine blades operate.

Answer 12

Converts gas energy (convergent shaped) from the combustion chamber into torque.
Impact of gas flow on the blades rotates the turbine.

Question 13

What is key about how an impulse turbine operates?

Answer 13

The turbine only rotates from gas flow impact on the rotor blades.

Question 14

What are the 3 configurations of turbine rotor blades?

Answer 14

Impulse.
Reaction.
Reaction - impulse.

Question 15

What is key about the fixed nozzle guide vanes in an impulse configuration and why ?

Answer 15

Due to their convergent shape, It is where the total pressure drop occurs at each stage.

Question 16

Describe the total pressure drop of an impulse turbine blade configuration?

Answer 16

It is too big.

Question 17

What does an impulse turbine blade configuration do to energy?

Answer 17

Converts all static pressure energy to kinetic energy.

Question 18

What do fixed nozzle guide vanes do in a pure reaction turbine blade configuration?

Answer 18

They alter gas flow direction without changing pressure.

Question 19

Describe the pressure drop of a pure reaction turbine blade configuration?

Answer 19

It is too little.

Question 20

What turbine blade configuration is normally used?

Answer 20

Reaction- impulse.
Known as a reaction turbine.

Question 21

Where does impulse force act in a reaction turbine blade configuration.

Answer 21

At the roots.

Question 22

Where does reactions force act on a reaction turbine blade configuration?

Answer 22

At the tip.

Question 23

How are turbine blades constructed?

Answer 23

They are precision cast as a single crystal.

Question 24

Why are the turbine blades single crystal?

Answer 24

Provides better strength and heat properties.

Question 25

What is done to turbine blades to keep them and the inlet nozzles cooler?

Answer 25

A ceramic coating is added.

Question 26

What does a ceramic coating on turbine blades allow for ?

Answer 26

A higher exhaust temperature, increasing the efficiency of the engine.

Question 27

Where are shrouded turbine blades used?

Answer 27

On low pressure turbines.

Question 28

What is the advantage of shrouded turbine blades?

Answer 28

Increased efficiency and vibration characteristics resulting in lighter stage weight.

Question 29

What is the purpose of the holes in turbine blades?

Answer 29

Purely for cooling.

Question 30

Define a turbine wheel.

Answer 30

A dynamically balanced unit of blades attached to a rotating disc.

Question 31

What is the turbine disc attached to ?

Answer 31

To the main transmitting shaft.

Question 32

What is the most common attachment for turbine blades?

Answer 32

Fir tree.

Question 33

What relieves stresses from hot gasses on the disc rim?

Answer 33

Bleeding cool air.

Question 34

What can be found on the rim of the turbine disc ?

Answer 34

Grooves for blade attachment.

Question 35

The turbine shaft must be capable of absorbing high torque loads. How is this achieved?

Answer 35

Welding the shaft to the disc.
Bolting.

Question 36

What is the purpose of a spine cut on the fwd end of the shaft?

Answer 36

Attachment for the shaft to the compressor rotor hub.

Question 37

Where is a splined coupling arrangement used?

Answer 37

On centrifugal compressor engines.

Question 38

What’s the most common method to retain turbine blades in grooves?

Answer 38

Peening.

Question 39

What is peening?

Answer 39

The blade is installed then the notch is filled by the disc metal.

Question 40

What is another method of blade retention?

Answer 40

Using the blade root as a stop and the other end has a tang bent to secure the blade in the disc.

Question 41

Where are nozzle guide vanes located in a turbine?

Answer 41

Aft of the combustion chamber.

Question 42

What is the primary purpose of the nozzle guide vanes?

Answer 42

To convert heat and pressure to velocity energy.

Question 43

What is the secondary purpose of the nozzle guide vanes?

Answer 43

Deflect gasses to a specific angle.

Question 44

How are nozzle guide vanes assembled?

Answer 44

Between inner and outer shrouds/rings.
Each vane fits into a contoured slot in the shrouds.

Question 45

How are turbine blades inspected for stress and creep?

Answer 45

Mainly visually.
Or dye penetrant.

Question 46

What can cause stress rupture cracks?

Answer 46

Overtemprature conditions.

Question 47

What is creep on turbine blades?

Answer 47

Slow structural deformation on a molecular level due to prolonged exposure to high stresses.

Question 48

What makes creep on turbine blades worse?

Answer 48

High temperatures.

Question 49

How big are turbine cracks types?

Answer 49

1/16 of an inch or bigger.