Gas Turbine - Turbine Section

Question 1

Impulse Turbine

Answer 1

NGV:
Velocity Up - “Vs Up”
Pressure decreases - “Ps down”
Temperature decreases

Rotor Blades:
Velocity down - “Vs down”
Pressure constant
Temperature constant

Question 2

Reaction Turbine

Answer 2

NGV:
Pressure constant
Velocity constant
Temperature constant

Rotor blade:
Pressure decreases
Velocity increase
Temperature decreases

Question 3

Rotor Blades are what in turbines

Answer 3

Twisted from root to tip
Root - impulse type
Mid section - 50% reaction
Tip - 100 reaction

Question 4

Purpose of Turbine

Answer 4

Convert Pressure and kinetic energy into mechanical energy for driving compressor.

Question 5

Rotor Blade Fitting

Answer 5

Fitted loosely to prevent sonic fatigue
Fir tree connection used
Flexible blades that change shape due to velocity

Question 6

Shrouding

Answer 6

Used to prevent tip looses

Question 7

Methods of turbine blade cooling

Answer 7

Convective Cooling - Large voids inside blade to promote heat transfer

Impingement - air passes through holes in LE/TE

Film - Air flows around edge of blades

Thermal Barrier Coating - increase resistance to high temps

Allow blade to operate in temps exceeding their melting point

Question 8

Active Clearance Control

Answer 8

Keeps tip distance to a minimum (optimal clearance)
Relative cooler air onto the casing to keep the casing from expanding
Controlled by FADEC
Not used on start/shut down to prevent rapid shrinking

Question 9

Root Section of turbine stage P/V/T (Impulse)

Answer 9

NGV:
Pressure decreases
Velocity increases
Temp decreases

Rotor:
Pressure same
Velocity decreases
Temp =

Question 10

50% along blade P/T/V

Answer 10

NGV:
Pressure decreases
Velocity increase
Temperature decreases

Rotor:
Pressure decreases
Velocity increase
Temperature decreases

Question 11

Tip of turbine blade T/P/V (Reaction Blade)

Answer 11

NGV:
Pressure =
Velocity =
Temp =

Rotor:
Pressure decreases
Velocity increases
Temperature decreases

Question 12

Blade Creep

Answer 12

Blade gets longer (finite life)
Centrifugal and high temps

Question 13

Single Crystal Turbine Blades

Answer 13

Does not have any ground boundaries therefore stronger at high temperatures

Question 14

Turbine source of cooling air

Answer 14

From the HP compressor at around 700 degrees

Question 15

High Cycle Fatigue

Answer 15

Large number of small stresses - high frequency vibrations for example

Question 16

Low Cycle Fatigue

Answer 16

Lower number of large stresses
Take off/thermal stress etc

Question 17

Turbine component that directs flow of gas at correct angle onto turbine blades is called

Answer 17

Nozzle Guide Vane

Question 18

Entire turbine is contained within a

Answer 18

Divergent air annulus