M15.6 Turbine Section

Question 1

What is the primary function of the gas generator turbine?

Answer 1

To absorb approximately 60 to 70% of the total pressure energy from the exhaust gases.

Question 2

Where is the turbine section located in a gas turbine engine?

Answer 2

Aft, or downstream, of the combustion chamber.

Question 3

What are the two types of turbines used in gas turbine engines?

Answer 3

• Radial flow turbine
• Axial flow turbine

Question 4

What is the advantage of radial flow turbines?

Answer 4

Simple design and easy to manufacture.

Question 5

What is a disadvantage of radial flow turbines compared to axial flow turbines?

Answer 5

Less efficient due to high aerodynamic losses and small airflow capacity.

Question 6

Which type of turbine is mainly used on modern gas turbine engines?

Answer 6

Axial flow turbine.

Question 7

What is the role of stationary turbine nozzle guide vanes?

Answer 7

To direct the gas flow onto the turbine rotor blades.

Question 8

What distinguishes an impulse turbine from other types?

Answer 8

It makes rotation solely by the impact of gas flow on the rotor blades.

Question 9

What characterizes the impulse configuration in turbine blades?

Answer 9

Total pressure drop occurs in the fixed nozzle guide vanes, converting all pressure energy to kinetic energy.

Question 10

What defines the reaction configuration in turbine blades?

Answer 10

Fixed nozzle guide vanes alter gas flow direction without changing pressure.

Question 11

What is a reaction-impulse configuration in turbines?

Answer 11

Combines both impulse and reaction forces acting on the blade.

Question 12

What is a common method of turbine blade retention?

Answer 12

Fir tree design.

Question 13

What materials are commonly used for turbine blades?

Answer 13

Alloy steel or precision-cast metals.

Question 14

What is the purpose of cooling air in turbine operation?

Answer 14

To relieve thermal stresses and maintain operational limits.

Question 15

What is creep in the context of turbine blades?

Answer 15

Slow structural deformation caused by prolonged exposure to high stresses.

Question 16

True or False: Radial flow turbines allow for high airflow and high thrust.

Answer 16

False.

Question 17

Fill in the blank: The turbine blades convert gas energy from the combustion chamber into _______.

Answer 17

[torque]

Question 18

What happens to the turbine blades at high temperatures?

Answer 18

They may experience stress rupture cracks and deformation.

Question 19

What is the significance of the turbine inlet nozzle vanes?

Answer 19

They convert heat and pressure energy to velocity energy for the turbine blades.

Question 20

What is the function of the turbine shaft?

Answer 20

To transmit the torque from the turbine wheels to the engine components.

Question 21

What is the effect of uneven workload on turbine blades?

Answer 21

Causes gases to exit from the blade at different velocities and pressures.

Question 22

What is a common inspection method for turbine blades?

Answer 22

Visual inspection, often aided by dye penetrant methods.

Question 23

What must be done if stress rupture cracks are found on turbine blades?

Answer 23

An over-temperature condition must be suspected and addressed.

Question 24

What are the two common methods for connecting the turbine shaft to the turbine disc?

Answer 24

• Welding
• Bolting

Question 25

What is the role of the turbine inlet guide vanes?

Answer 25

To prepare mass airflow to drive the turbine rotor.

Question 26

What is the purpose of the grooves or notches in the turbine disc rim?

Answer 26

To allow attachment of turbine blades and accommodate thermal expansion.

Question 27

What is creep in the context of turbine blades?

Answer 27

Creep is a phenomenon caused by prolonged exposure to high stresses that results in visible dimensional changes to the blades. ## Footnote Creep increases with temperature, especially in the turbine area of a turbine engine.

Question 28

What can cause dimensional inconsistency in turbine blades?

Answer 28

Dimensional inconsistency could be caused by creep rather than over-temperature. ## Footnote Creep leads to gradual deformation of materials over time under constant stress.

Question 29

How should turbine blades be inspected and measured?

Answer 29

In accordance with the manufacturer's instructions. ## Footnote This ensures compliance with safety and performance standards.

Question 30

What might signs of scoring on the turbine case indicate?

Answer 30

The length of the turbine blades is out of tolerance. ## Footnote Scoring can be a sign of blade contact or wear that needs to be addressed.

Question 31

What should be done when observing and measuring blade deformation?

Answer 31

Adhere to all manufacturer's specifications and replace any damaged turbine blades as specified. ## Footnote Following specifications helps maintain engine performance and safety.

Question 32

What should be checked on individual blades and the turbine disc?

Answer 32

Check individual blades for stretch and the turbine disc for hardness and stretch. ## Footnote This ensures that the components are within operational limits.

Question 33

What is the protocol for reinstalling blades removed for inspection?

Answer 33

Blades must be reinstalled in the same slots/position from which they were removed. ## Footnote This maintains the blade's original orientation and balance.

Question 34

Before removing blades for inspection, what should be done?

Answer 34

Number the blades before removal. ## Footnote This helps in correctly reinstalling them in their original positions.