Axial Flow Turbines

Question 1

What are 5 summary points of turbine blade design?

Answer 1

Turns flow away from engine axis
Flow area decreases (to a minimum at the throat)
Average velocity increases
Average pressure decreases
Extracts energy from the hot gases and drives the compressor

Question 2

What is the flow accelerated by in the absolute frame?

Answer 2

The stator

Question 3

What is the flow accelerated by in the relative frame?

Answer 3

The rotor

Question 4

In the absolute frame, where does the flow leave slower?

Answer 4

The flow leaves the rotor slower than it left the stator

Question 5

What’s the difference between an Impulse Turbine and a Reaction Turbine?

Answer 5

Impulse turbine - all pressure drop is in the nozzle effect on the blades is momentum only
Reaction turbines - pressure drop in both rotor and stator

Question 6

What does the Stage Loading (Temperature Drop) coefficient do?

Answer 6

Defines how much work can be obtained from a stage - the higher the better, but usually at the cost of efficiency

Question 7

What’s the definition of the Degree of Reaction?

Answer 7

How much of the expansion takes place in the rotor verses how much across the stage