Design of Components of Francis Turbine P M V Subbarao Professor Mechanical Engineering Department Detailing to Infuse Reaction…

Design of Components of Francis Turbine

P M V SubbaraoProfessor

Mechanical Engineering Department

Detailing to Infuse Reaction….

Specific speed in rpm4

5H

PNN s

P in hp & H in meters

Selection of Speed of A Turbo Machine

Hzfforz

Np

503000

Zp : Number of pairs of poles of the generator

Design of Any Selected Francis Turbine Unit

• Different capacities for each sub-group.• Design for Normal Head.• Assume an overall efficiency: 94 – 96%• Calculate the required flow rate.

HgQP Francis

General Layout of A Hydro Power Plant

Power Tunnel:Diameter: 15000mmLength= 746mSlope= 1 in 120Actual velocity: 5.563m/s

Power Tunnel

hgD

fVS

2

4 2

0

Channel Bed Slope

P

ADh

4

Penstock : Consider Velocity equal to Actual Site Velocity

penstock

penstockfriction gd

fLVHxh

2

4 2

2

9.0Re

74.57.3

log

0625.0

hD

kf

Pipe Material Absolute Roughness, emicron

(unless noted)

drawn brass 1.5drawn copper 1.5commercial steel 45wrought iron 45asphalted cast iron 120galvanized iron 150cast iron 260wood stave 0.2 to 0.9 mm

concrete 0.3 to 3 mm

riveted steel 0.9 to 9 mm

Estimate net Head available at the inlet turbine casing

Dimensions of Guide Vane Wheel

Group NO.

Unit SizeMW

Degree of Reaction, %

Dpenstock

mVpenstock

m/sHead loss

m

1

135.9

35

2 40

3 45

4

203.9

35

5 40

6 45

Design of Spiral Casing

Rcasing

Risv

dpenstock

Q

Inlet to Stay vanes

Guide vanes R

ing Stay vanes Ring

Runner

Design of the Guide VanesHow to choose the guide vane angle egv at full load

11344 2 egv

egv

Q

gH2/

gHQQ 2/

Specifications of Guide Vanes

• Slow Runner: Ns=60 to 120

– Begv/Dmgv=0.033 – 0.04

• Normal Runner: Ns = 120 – 180

– Begv/Dmgv=0.125 to 0.25

• Fast Runner: Ns = 180 to 300

– Begv/Dmgv=0.25to 0.5L: length of vane

L=15 to 30% of Degv

Dimensions of Guide Vane Wheel

Group NO.

Unit SizeMW

Degree of Reaction, %

Digv, m Degv, m Bgv, m

1

135.9

35

2 40

3 45

4

203.9

35

5 40

6 45

Design of the Guide Vane Outlet Angle

• The outlet angle can be calculated by assuming a vortex from the flow in the gap between the runner and the guide vanes

nwigv

nwegv igvegv

rVrV

egvegvfegv BD

QV

regv

rigv

Begv

Select appropriate value of n

Design of the Details of Stay Vanes

StayVaneinletStayVaneinletwGuideVaneinletGuideVaneinletw rVrV

rexit stay Vane

rinlet Stay Vane

Besv

Theory of Relatively Whirling flow:

Bisv

isvn

wisvesvn

wesv rVrV

isvSratyVaneinletStayVaneinletf BD

QV

penstockStayVaneainlet VV

At any angle , the radius of casing is:

penstockisv dRR2casing

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

2QQ

In general =1.0, however corrected using CFD.

Performance of Casing : Loss of Total Pressure

Rcasing

Risv

dpenstock

Q

The losses in the spiralcasing as a sum f distributed losses and the exit losses

exitflscfscf hhh ,,,

g

V

d

lh sc

chspelscf 2

2

,,

222

2

, 8 isvisvexitf Bgr

Qh

02.001.0 25.01.0

Gap losses

Friction losses in the spiral casingand stay vanes

Guide vane losses

Friction losses

Runner losses

Draft tube losses

Number of Guide/stay Vanes

Ns Z=8 10 12 14 16 18 20 24

<200

Dge,mm

<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

Validation of the Guide Vanes DesignDegree Overlapping of the guide vanes

Low Overlap High Overlap

Specifications of Guide Vanes

L: length of vane

L=15 to 30% of Degv

Minimum Number of Guide/stay Vanes

Ns Z=8 10 12 14 16 18 20 24

<200

Dge,mm

<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

The Runner

Velocity triangles

rri

rre

Uri

Vwi

Vri

Vfi

Vai

Ure

Vwe

Vre

Vfe

Vae

i

i

ee

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

Diameter of guide vane shaft Vs Runner Inlet Diameter

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

DRI

DRE

07,129,0 RI

mgv

D

D

gH2/

Dmgv

Design of the Runner 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

Ub

Vwi

Vai

VfiVri

Ub

Vwi

Vai Vfi

Vri

VwiUb

Vai

Vfi

Vri

Inlet Velocity Triangles Vs Ns

Low Specific Speed : Slow Francis Runner

Vwi

Vai

Vfi


Low Specific Speed : Normal Francis Runner

Vwi

Vai

Vfi


High Specific Speed : Fast Francis Runner

Vwi

Vai

Vfi

Specifications of Runner

• Slow Runner: Ns=60 to 120 to 250

– Kui = 0.62 to 0.68 to

– Bgv/Dmgv=0.04 – 0.033• Normal Runner: Ns = 120 – 180

to 32.50

– Kui = 0.68 to 0.72 – Bgv/Dmgv=0.125 to 0.25

• Fast Runner: Ns = 180 to 300 to 37.50

– Kui = 0.72 to 0.76 to

– Bgv/Dmgv=0.25to 0.5

Velocity triangles

rri

rre

Uri

Vwi

Vri

Vfi

Vai

Ure

Vwe

Vre

Vfe

Vae

i

i

ee

rU

UU

r

rire

13o < e < 22o

Design for Maximum Power

draftfte

RETEtwatmare

RE pV

gzgzgHpV

p ,

22

22

Net Positive Suction Head, NPSH

NPSH required

g

Ub

g

VaNPSH refre

R

22

22

15.005.0

15.105.1

b

a

Turbines

Dimensions of the outlet

g

UbUa

g

Ub

g

VaNPSH reererefre

R 2

tan

22

2222

13o < e < 22o

1,05 < a < 1,150,05 < b < 0,15

Highest value for highest head

Extra head to be converted into kinetic energy:

Remaining head to be used :

extraremainingrire HH

g

VV

2

22

Preferred Exit Velocity Triangle:

13o < RE < 22o

DRI

DRE

Available Inlet velocity Triangle

Runner Design

Documents

Design of Components of Francis Turbine P M V Subbarao Professor Mechanical Engineering Department Detailing to Infuse Reaction…