1. TURBINES

2. Flash back your memory…
What is turbomachine?
A turbomachine is a steady flow device (non-positive displacement) which creates/consumes shaft-work by changing the moment of momentum (angular momentum) of a fluid passing through a rotating set of blades.

3. What is in this section? Understand the classification of turbines.
Analysis of the flow in the blade rows and stages.
Dynamic scaling, characteristics of compressors and turbines.
Compressible flow machines.
Hub-tip variations in flow properties.

4. Examples of turbines

5. Examples of turbines

6. Aero Engines & aero Derivatives
Examples of turbines:
Aero Engines & aero Derivatives

7. Another example: Hydro turbines

8. IMPULSE REACTION TURBINES FLOW VELOCITY VELOCITY TRIANGLES
TURBINES TYPES
IMPULSE
REACTION
CONTROL VOLUME
FLOW VELOCITY
VELOCITY TRIANGLES
DIMENSIONAL ANALYSIS
TURBINES

9. Dynamic turbine classifications
Impulse turbine
Flow converts into kinetic energy.
Eg. Pelton wheel
Reaction turbine
Momentum is exchanged between the fluid, there is large pressure drop.
Eg. Francis turbine and Kaplan turbine

10. Impulse turbine: Pelton wheel.

11. Impulse turbine: Pelton wheel. The insight

12. Impulse turbine: Pelton wheel.

13. Impulse turbine: Pelton wheel. The insight

14. Impulse turbine: Pelton wheel. Velocity diagram

15. Reaction turbine

16. Subcategories of reaction turbines

17. Reaction turbine: Francis turbine

18. Typical set-up and terminology for hydroelectric plant: Francis turbine

20. Figure 14.95: Outer radius runner
Equation 14.45

21. Figure 14.96: Inner radius runner
Equation 14.46

22. Figure 14.99: The control volume from inlet to the outlet runner (Francis turbine)

23. Further classification
Type and arrangement of staging
Direction of steam flow
Repetition of steam flow
Division of steam flow

24. Flow velocity and flow triangles (basic coordinate systems and velocities)
Earlier we defined a turbomachinery as a steady flow device which creates/consumes shaft-work by changing the momentum of a fluid through a rotating set of blades. Therefore we must consider: the moment of momentum rotation about an axis

25. Flow velocity and flow triangles

26. Flow velocity and flow triangles

27. The analysis of the flow through rotating blade rows (rotors) can be greatly simplified by working in a frame of reference so that the rotors appear to be at rest.
Axial view of the components of the absolute and rotor relative velocity vectors.

28. The two (stationary/absolute and rotational/rotor relative) frames of reference are related according to the vector expression: Absolute velocity=relative velocity + rotational velocity Since Vx and Vr are same in both frames of reference, the only difference between the absolute and relative velocities is due to the magnitude of the circumferential velocity.

29. Velocity triangles for an axial turbine stage (stator and rotor)
For simplicity, we assume that:
The variation of the flow in the radial direction is small.
The radial component of velocity is negligible (Vx=0).
There is no large change in radius (r)through the stage.
The blade speed ( ) is constant.
The direction of the flow in the circumferential direction is small.
We recall that  the flow angles are positie if they are in the same direction as the rotation of the rotor.

30. Now, turbines use stators to create a moment of momentum which is then removed in the rotor.

32. Note that, the analysis of the flow through rotating blade rows (rotors) can be greatly simplified by working n a frame of reference so that the rotors appear to be at rest. We recall that the axial velocity, Vx2 is the same in both frames of reference and that
Therefore, the rotor relative inlet flow angle is given by

33. We now look at the rotor exit:

34. At the rotor exit, we note that,
And that;

35. Conclusion… Turbine blades make the flow more tangential
This is very common
Turbine blades accelerate the flow
Boundary layers thin and losses in efficiency are small.

36. Example
The flow leaving an axial turbine stator blade row has a velocity 700m/s at an angle of 70˚. The rotor has a blade speed of 500m/s. the flow leaving a rotor blade row also has a relative velocity of 700m/s at a relative angle of -70˚. Neglect any radial velocities and assume that the axial velocity is constant through the stage, calculate the relative flow angle at rotor inlet and the absolute flow angle at rotor exit.

37. Example 14.16 – Turbine specific speed.
Turbine scaling laws
Example – Turbine specific speed.

38. Questions
14.68C Why turbines often have greater efficiencies that do pumps? 14.69C Discuss the main difference between in the way that dynamic pumps and reaction turbines are classified as centrifugal (radial), mixed flow or axial C Name briefly describe the differences between the two basic types of dynamic turbine C Discuss the meaning of reverse swirl in reaction hydro turbines and explain why some reverse swirl may be desirable. Support your answer with an equation. Why is it not wise to have too much swirl? Discuss.