sprial casing report
15
Parts of Sprial casing satish 12S/ME145 Mechanical Engineering Department
description
for fluid mech.
Transcript of sprial casing report
Parts of Sprial casing
satish12S/ME145
Mechanical Engineering Department
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 ?
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
Mega Civil Works for Mechanical Power Generation
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.
Global Symmetric Flow Domain through Statinary Vanes
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 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
