Design Analysis of Parts of Francis Turbine

P M V SubbaraoProfessor

Mechanical Engineering Department

Provision of Features to Blend some Reaction into Impulse…

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.

Design of Spiral Casing

Rcasing

Risv

dpenstock

Q

How to select Q ?

Spiral Casing for 35 MW Vertical Francis Turbine

Design of Spiral Casing

Rcasing

Risv

dpenstock

Q Select a suitable value of discharge per unit: Q

2

4 penstockpenstock dVQ

But maximum allowable value is 10 m/sMaximum allowable head loss in Penstock =2 to 4% of available head

At any angle , the radius of casing is:

penstockisv dRR

2casing

A full spiral is generally recommended for high head 300m, semi-spiral is recommended for low head < 50m.

2QQ

In general =1.0, however corrected using CFD.

Flow Distribution Analysis of Casing

Stay vanes or Guide vanes

Static Pressure Distribution in Casing.

Mega Civil Works for Mechanical Power Generation

Parts of A Francis Turbine

Geometrical Description of A Francis Turbine Parts

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.

Design of Guide Wheel (Stator): Low Specific Speed

Design of Guide Wheel (Stator): High Specific Speed

Q

gH2/

gHQQ 2/

Design of the Guide VanesDiameter of guide vane shaft

1,0

1,1

1,2

1,3

1,4

1,5

1,6

1,7

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6

Speed number

Dia

met

er R

atio

D0/

D1

D1

D2

07,129.01

0 D

D

gH2/

Design of the Details of Stay & Guide Vane Wheels

• The inlet angle can be calculated by assuming a free vortex from the flow coming from the spiral casing

StayVaneinletStayVaneinletwGuideVaneinletGuideVaneinletw rVrV

giGuideVaneinletGuideVaneinletf BD

QV

rinlet Guide Vane

rinlet Stay Vane

Bgi Bsi

Theory of Relatively free Whirling flow:

gHkV wgoguideVaneexitw 2

34.1 to7.0wgok

Pressure drop versus discharge

Pressure drop versus Flow Rate

Global Symmetric Flow Domain through Statinary Vanes

Operational Configurations of Guide Vanes

The correlation between the turbinedischarge and the guide vane opening angle.

Pressure drop versus guide vane angle

Design of the Guide Vanes

11344 2 go

Q

gH2/

gHQQ 2/

How to choose the guide vane maximum angle 0 at full load ?

Design of the Guide VanesLevel of Overlapping of the guide vanes

Design of Guide Vanes

Guide vane at DesignPosition = 12.21°

Guide vane at closed position

Guide vane at Max. openPosition = 18°

.

L=15 to 30% of D go

L: length of vane

Guide vanesGuide vanesGuide vanesGuide vanesGuide vanesGuide vanes

Runner inlet (Φ 0.870m)

Guide vane outlet for designα) (Φ 0.913m)

ClosedPosition

Max. Opening Position

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

nriwgi

ngowgo rVrV

00 ggfo BD

QV

rri

Dg0

Bg0

gHkV fofo 2

0.6 to3.0fok

Design of the Guide VanesHow to choose the number of vanes

• The number of guide vanes has to be different from the number of runner vanes.

Integerz

z

VanesRunner

VanesGuide

R a d i a l v i e wrunner guide vanes and stay vanes

R a d i a l v i e wrunner guide vanes and stay vanes

R a d i a l v i e wrunner guide vanes and stay vanes

R a d i a l v i e wrunner guide vanes and stay vanes

R a d i a l v i e wrunner guide vanes and stay vanes

R a d i a l v i e wrunner guide vanes and stay vanes

R a d i a l v i e wrunner guide vanes and stay vanes

R a d i a l v i e wrunner guide vanes and stay vanes

R a d i a l v i e wrunner guide vanes and stay vanes

R a d i a l v i e wrunner guide vanes and stay vanes

R a d i a l v i e wrunner guide vanes and stay vanesR a d i a l v i e wrunner guide vanes and stay vanes

Water from spiral casing

Water particle

Number of guide vanes

16

18

20

22

24

26

28

30

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6

Speed Number

Nu

mb

er o

f G

uid

e V

anes

gH2/

Number of Guide Vanes

Ns

Dge,mm

Z=8 10 12 14 16 18 20 24

<200 <250 250 - 400

400 - 600

600 - 800

800 - 1000

1000 1250

1250 1700

>1700

>200 <300 300 - 450

450 - 750

750 - 1050

1050 1350

1350 1700

1700 2100

>2100

min

hpin

s

H

PNN

4/5

The Runner

Mean Velocity triangles Across Runner

rU

UU

r

rire

Velocity trianglesrri

rre

Uri

Vwi

Vri

Vfi

Vai

Ure

Vwe

Vre

Vfe

Vae

i

i

ee

rU

UU

r

rire

The transposition of the profiles for all the 11 streamlines

UbVwi

Vai

VfiVri

Ub

Vwi

Vai Vfi

Vri

VwiUb

Vai

Vfi

Vri