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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