nozzles & jets for pelton wheels a special device to implement pure momentum based energy...
TRANSCRIPT
Nozzles & Jets for Pelton Wheels
A Special Device to implement Pure Momentum based Energy
Exchange…….
P M V SubbaraoProfessor
Mechanical Engineering Department
Key Parts of Pelton Turbine
Design Of Intake for High Release of Powerpatm
H 2
2
,penstock
PSpTfatmexitPS
VhHgpp
nozzlefPSPTfjet hhHg
V,,
2
2
Multi Jet Distributors for Pelton Wheels
Discharge Distribution And Flow Energy Losses In the Distributor
Q/QBEP
CFD Analysis of Free Jets & Flows In Air
A Consultancy Project Sponsored ByBHEL, Bhopal2008 -- 2009
The set of governing equations solved were primarily the continuity and the momentum equations.
These basic equations in Cartesian coordinate system for incompressible flows are given below,
Governing Differential Equations
Arrangement of Jets
CAD Model of Distributor
Pelton Wheel Flow Distributor
Static Pressure Distribution
Distribution of Velocity Magnitude
Exit Velocities
The area averaged values for the various critical sections are listed below,
Inlet : 20.77 ms-1Outlet 1 : 25.37 ms-1Outlet 2 : 18.13 ms-1Outlet 3 : 17.05 ms-1Outlet 4 : 16.91 ms-1Outlet 5 : 15.22 ms-1Outlet 6 : 9.75 ms-1
Feedback
• It is evident from the area averaged values of velocity and the mass fluxes at the outlet that the flow distribution is not exactly uniform.
• The flow at outlets 2, 3, 4, 5 is almost equal, however, flow at outlet -1 is high and outlet -2 is low.
• The uniformity of flow distribution may be restored by employing variable openings using the spears provided inside the injection nozzle along with possible alterations in the rate of curvature of distributor especially in the region of outlet-6.
Closing Remarks : Multi Jet Pelton Wheel
• Higher rotational speed
• Smaller runner
• Simple flow control possible
• Redundancy
• Can cope with a large range of flows
But
• Needs complex manifold
• May make control/governing complex
A Complex Engineering Micro Alternate To Simple Gigantic Natural System
Flow Control using Spear & Nozzle System
Free Surface Expansion Shape for Maximum Power
nozzlefPSPTfjet hhHg
VMaximize
Maximize
,,
2
2
Jet ofPower Kinetic
nozzlefhMinimize ,
Simplification of Nozzle Shape
d0djet,VC
The nozzle and spear are perfectly streamlined to reduce friction losses and achieve perfect circular jets.
Geometrical Relations for Nozzle
The values of α varies between 20 to 30° whereas β varies from 30 to 45°.
Industrial Correlations for Jet Area variation with stroke
Optimal value of Outlet jet area, ao
2BsAsao
s is the displacement of spear
sinsin2 orA
2
2
sin
sinsinsinB
Discharge through a Spear Nozzle
if ao is the jet area at nozzle outlet section and knowing that this is dependable on the stroke s of the needle tip, the water velocity for this section is:
gHKV voOjet 2,
Then, the corresponding flow rate is:
gHKBsAsVaQ voOjetOjet 22,
Discharge Control using Spear Nozzle
Linear Rate of Change Discharge w.r.t Stroke
Geometrical Relations for Nozzle
dO
2dO – 2.4dO
5dO – 9dO
0.8dO – 0.9dO
1.2dO – 1.4dO
1.1dO – 1.3dO
Performance Analysis of Nozzle-Spear Valve
Ideal Nozzle-spear Valve:
constant2
2
gzV
p
Along flow direction
nozzleftotal ΔppVp
,
2
-constant2
Real Nozzle-spear Valve:
penstock
penstockfriction d
fLVp
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
Numerical Computation of Total Pressure Variation
gHKV vactualVCjet 21:, 99.098.0 1 vK
Jet carrying a discharge of Q to deliver a power P
gHKdQ vVCjet 24 1
2,
To generate a discharge of Q, we need a least jet diameter of
gHK
Qd
v
VCjet2
4
1
,
QgHP turbine
Acceptable Performance of Nozzle
Diameter of the Jet at the outlet, do
gHKdQ voo 24
2
83.081.0 vOK
It is important to find out the VC and outlet jet diameters/areas
The Diameter of Jet before Reaching Bucket