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Design Analysis of Parts of Francis
Turbine
P M V Subbarao
Professor
Mechanical Engineering Department
Provision of Features to Blend some
Reaction into Impulse…
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p
Spiral Casing
• Spiral Casing : The fluid enters from the penstock to a spiralcasing which completely surrounds the runner.
• This casing is known as scroll casing or volute.
• The cross-sectional area of this casing decreases uniformly alongthe circumference to keep the fluid velocity constant in
magnitude along its path towards the stay vane/guide vane.
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Design of Spiral Casing
Rcasing
Risv
d penstock
Q
How to select !
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Spiral Casing for "# $% &ertical 'rancis Tur(ine
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Design of Spiral Casing
Rcasing
Risv
d penstock
Q Select a suita(le value of
discharge per unit) Q
*
+ penstock penstock d V Q
π =
,ut maimum allowa(le value is m/s
Maximum allowable head loss in Penstock =2 to 4% o
available head
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0t any angle θ 1 the radius of casing is)
penstock isv d R Rπ κθ *
casing +=
0 full spiral is generally recommended for high head "m1 semi-spiral
is recommended for low head 2 #m!
π θ θ *
QQ =
3n general κ 4.1however corrected
using C'D.
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'low Distri(ution 0nalysis of Casing
Stay vanes or 5uide vanes
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Static 6ressure Distri(ution in Casing.
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$ega Civil %orks for $echanical 6ower 5eneration
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6arts of 0 'rancis Tur(ine
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5eometrical Description of 0 'rancis Tur(ine 6arts
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Stay &anes 7 5uide &anes
• The (asic 6urpose of the stay vanes 7 guide vanes is to converta part of pressure energy of the fluid at its entrance to the kineticenergy and then to direct the fluid on to the runner (lades at theangle appropriate to the design.
• $oreover1 the guide vanes are pivoted and can (e turned (y asuita(le governing mechanism to regulate the flow while theload 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 (efore its entry to the runner.• The guide vanes are constructed using an optimal aerofoil shape1
in order to optimi8e off-design performance.
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Design of 5uide %heel 9Stator:) ;ow Specific Speed
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Design of 5uide %heel 9Stator:) High Specific Speed
−−−−
⋅=Ω Qω
g" */ω ω =−−
g" QQ */=−−
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Design of the 5uide &anes
Diameter 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
D i a m e t e r R a t i o
D 0 / D 1
D
D*
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Design of the Details of Stay 7 5uide &ane %heels
• The inlet angle can (e calculated (y
assuming a free vorte from the
flow coming from the spiral casing
$taVaneinlet $taVaneinlet w&uideVaneinlet &uideVaneinlet w ' V ' V ⋅=⋅
gi&uideVaneinlet
&uideVaneinlet
( #
QV
⋅⋅
=
π
r inlet ui!e "ane
r inlet #tay "ane
Bgi Bsi
Theory of >elatively free %hirling flow)
g" k V wgo guideVaneexit w * =
"+.to
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6ressure drop versus discharge
6ressure drop versus 'low >ate
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5lo(al Symmetric 'low Domain through Statinary
&anes
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?perational Configurations of 5uide &anes
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The correlation (etween the tur(ine
discharge and the guide vane opening angle.
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6ressure drop versus guide vane angle
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Design of the 5uide &anes
( ).."++ * +Ω⋅+Ω⋅−⋅= go
α
α ο
−−−−
⋅=Ω Qω
g" */ω ω =−−
g" QQ */=−−
How to choose the guide vane maimum angle α
at full
load !
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Design of the 5uide &anes
;evel of ?verlapping of the guide vanes
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Design of Guide Vanes
ui!e $ane at Design
Position % 12&21'
ui!e $ane at close! (osition
ui!e $ane at )a*& o(enPosition % 18'
&
4 . # t o " / @
o f # g o
; ) l e n g
t h o f v a
n e
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Guide vanesGuide vanesGuide vanesGuide vanesGuide vanesGuide vanes
+unner inlet
(Φ 0.870m)
ui!e $ane outlet for !esign(Φ 0.913m)
Closed
Positiona!. "penin#
Position
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Design of the 5uide &ane ?utlet 0ngle
• The outlet angle can (e calculated (y assuming a free vorte from
the flow in the gap (etween the runner and the guide vanes
n
'iwgi
n
gowgo ' V ' V ⋅=⋅
g g
o ( #
QV
⋅⋅= π
r ri
Dg0
Bg0
g" k V o o *=
.Ato".= ok
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Design of the 5uide &anes
How to choose the num(er of vanes
• The num(er of guide vanes has to (e different
from the num(er of runner vanes.
)ntege' *
*
Vanes Runne'
Vanes&uide≠
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R a d i a l v i e w
runner guide vanes and stay vanes
R a d i a l v i e w
runner guide vanes and stay vanes
R a d i a l v i e w
runner guide vanes and stay vanes
R a d i a l v i e w
runner guide vanes and stay vanes
R a d i a l v i e w
runner guide vanes and stay vanes
R a d i a l v i e w
runner guide vanes and stay vanes
R a d i a l v i e w
runner guide vanes and stay vanes
R a d i a l v i e w
runner guide vanes and stay vanes
R a d i a l v i e w
runner guide vanes and stay vanes
R a d i a l v i e w
runner guide vanes and stay vanes
R a d i a l v i e w
runner guide vanes and stay vanesR a d i a l v i e w
runner guide vanes and stay vanes
$ater %rom
spiral &asin#
$ater
parti&le
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Bum(er of guide vanes
16
18
20
22
24
26
28
30
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
Speed 'umber
'
u m b e r o % ( u i d e ) a n e s
g" */ω ω =−−
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Bum(er of 5uide &anes
Bs
Dge1mm
4 * + A * *+
2* 2*# *# -+ + -A A - - *# *#
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The >unner
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$ean &elocity triangles 0cross >unner
ω ' ,
, ,
'
'i'e
=
<
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&elocity triangles
' 'i
' 'e
, 'iV wi
V 'iV i
V ai
, 'eV we
V 'eV e
V ae
β i
α i
β eα e
ω ' ,
, ,
'
'i'e
=
<
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The transposition of the profiles for all the streamlines
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, b V wi
V ai
V iV 'i
, b
V wi
V ai V i
V 'i
Vwi, b
V ai
V iV 'i