15.6 turbines

Question 1

what is the sole purpose of the gas generator turbine

Answer 1

absorb approx 60 - 70% of total pressure energy from exhaust gases

Question 2

where is turbine located on engine

Answer 2

aft of the combustion chamber

Question 3

what are the 2 types of turbines on gas turbine engine

Answer 3

radial flow and axial flow

Question 4

what is the first component of a turbine

Answer 4

stationary vanes

Question 5

how many stages are radial flow turbines

Answer 5

always single stage turbines

Question 6

where can radial flow turbines be found

Answer 6

apu
small gas turbine engines

Question 7

what are the disadvantages of radial flow turbines compared to axial flow

Answer 7

only allow small airflows
less efficient - high aerodynamic losses

Question 8

which engines use axial flow

Answer 8

mainly used on modern gas turbine engines

Question 9

whats better axial or radial

Answer 9

axial

Question 10

how is gas flow in the combustion chamber accelerated

Answer 10

due to a convergent shape of ducts between nozzle guide vanes and deflected towards the direction of rotation of the turbine blades

Question 11

what do the turbine blades rotate

Answer 11

rotates a turbine shaft which moves the compressor

Question 12

what are the rotor blades called

Answer 12

impulse blades

Question 13

difference between reaction turbine vs impulse turbine

Answer 13

reaction doesnt change the pressure of the gas

Question 14

why does the impulse config cause a pressure drop

Answer 14

causes a pressure drop due to the convergent shape
increase gas velocity whilst reducing pressure

Question 15

what do most normal turbine enginse have

Answer 15

impulse reaction config

Question 16

how are most turbine blades cast

Answer 16

as a single crystal - gives the blades better strength and heat properties

Question 17

pros of shrouded turbine blades

Answer 17

improve efficiency and vibration

Question 18

cons of shrouded turbine blades

Answer 18

limits turbine speed and requires more blades

Question 19

what is the turbine wheel

Answer 19

when the turbine blades are installed onto the disc

Question 20

how can you relieve the stresses on the disk

Answer 20

bleed cooling air back onto the face of the disk

Question 21

why is there space between disk and turbine blades

Answer 21

to allow for thermal expansion

Question 22

most common method to attach turbine blades

Answer 22

fir tree

Question 23

how are the blades retained in the grooves

Answer 23

peening, welding, locktabs , riveting

Question 24

what is turbine shaft usually fabricated from

Answer 24

alloy steel

Question 25

what is most common method to retain the blades in the groove

Answer 25

peening

Question 26

where is the turbine inlet nozzle vanes found

Answer 26

located directly aft of combustion chamber and immediately fwd of turbine wheel

Question 27

where are the hottest temps in the engine found

Answer 27

turbine inlet nozzle vanes

Question 28

what action should happen if there are cracks on turbine disk

Answer 28

replacement of disk and turbine rotor

Question 29

how can slight pitting be fixed on turbine

Answer 29

stoning and polishing

Question 30

how are turbine blades inspected for stress rupture cracks and deformation of leading edge

Answer 30

strong light and magnifying glass

Question 31

how do stress rupture cracks appear on leading edge or trailing edge

Answer 31

as minute hairline cracks - at a right angle to the edge length

Question 32

how may deformation caused by overtemperature may appear along leading edge

Answer 32

as waviness

Question 33

how big are visible cracks

Answer 33

above 1/16th inch

Question 34

what is creep

Answer 34

slow structural deformation on a molecular level

Question 35

what causes creep to increase

Answer 35

extreme temps in the turbine area