1. Design Analysis of Parts of Francis Turbine
P M V Subbarao
Professor
Mechanical Engineering Department
Provision of Features to Blend some Reaction into Impulse…

2. Spiral Casing
Spiral Casing : The fluid enters from the penstock to a spiral casing which completely surrounds the runner.
This casing is known as scroll casing or volute.
The cross-sectional area of this casing decreases uniformly along the circumference to keep the fluid velocity constant in magnitude along its path towards the stay vane/guide vane.

3. Design of Spiral Casing
dpenstock
Rcasing Q
Risv
How to select Q ?

4. Spiral Casing for 35 MW Vertical Francis Turbine

5. Design of Spiral Casing
dpenstock
Rcasing Q
Select a suitable value of discharge per unit: Q
Risv
But maximum allowable value is 10 m/s
Maximum allowable head loss in Penstock =2 to 4% of available head

6. At any angle q, the radius of casing is:
A full spiral is generally recommended for high head 300m, semi-spiral is recommended for low head < 50m.
In general k =1.0, however corrected using CFD.

7. Flow Distribution Analysis of Casing
Stay vanes or Guide vanes

8. Static Pressure Distribution in Casing.

9. Mega Civil Works for Mechanical Power Generation

10. Parts of A Francis Turbine

11. Geometrical Description of A Francis Turbine Parts

12. Stay Vanes & Guide Vanes
The basic Purpose of the stay vanes & guide vanes is to convert a part of pressure energy of the fluid at its entrance to the kinetic energy and then to direct the fluid on to the runner blades at the angle appropriate to the design.
Moreover, the guide vanes are pivoted and can be turned by a suitable governing mechanism to regulate the flow while the load changes.
The guide vanes are also known as wicket gates.
The guide vanes impart a tangential velocity and hence an angular momentum to the water before its entry to the runner.
The guide vanes are constructed using an optimal aerofoil shape, in order to optimize off-design performance.

13. Design of Guide Wheel (Stator): Low Specific Speed

14. Design of Guide Wheel (Stator): High Specific Speed

15. Design of the Guide Vanes Diameter of guide vane shaft

16. Design of the Details of Stay & Guide Vane Wheels
Theory of Relatively free Whirling flow:
Bsi
Bgi
The inlet angle can be calculated by assuming a free vortex from the flow coming from the spiral casing
rinlet Stay Vane
rinlet Guide Vane

17. Pressure drop versus discharge
Pressure drop versus Flow Rate
Pressure drop versus discharge

18. Global Symmetric Flow Domain through Statinary Vanes

19. Operational Configurations of Guide Vanes

20. The correlation between the turbine discharge and the guide vane opening angle.

21. Pressure drop versus guide vane angle

22. Design of the Guide Vanes
How to choose the guide vane maximum angle a0 at full load ? ao

23. Design of the Guide Vanes Level of Overlapping of the guide vanes

24. Design of Guide Vanes .
L: length of vane
L=15 to 30% of Dgo

25. Max. Opening Position Closed Position
Runner inlet (Φ 0.870m)
Guide vane outlet for designα) (Φ 0.913m)
Max. Opening Position
Closed
Position

26. Design of the Guide Vane Outlet Angle
The outlet angle can be calculated by assuming a free vortex from the flow in the gap between the runner and the guide vanes
Dg0
Bg0
rri

27. Design of the Guide Vanes How to choose the number of vanes
The number of guide vanes has to be different from the number of runner vanes.

28. Water particle
Water from spiral casing

29. Number of guide vanes

30. Number of Guide Vanes Ns Z=8 10 12 14 16 18 20 24 <200 <250
Dge,mm
Z=8 10 12 14 16 18 20 24
<200
<250
>1700
>200
<300
>2100

31. The Runner

32. Mean Velocity triangles Across Runner

33. Velocity triangles rri rre Uri Vwi Vri Vfi Vai Ure Vwe Vre Vfe Vae bibe ae

34. The transposition of the profiles for all the 11 streamlines

35. Ub
Vwi
Vai
Vfi
Vri Ub
Vwi
Vai
Vfi
Vri
Vwi Ub
Vai
Vfi
Vri