Nozzles

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Nozzles Jets for Pelton Wheels
P M V Subbarao Professor Mechanical Engineering
Department
A Special Device to implement Pure Momentum based
Energy Exchange.
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Key Parts of Pelton Turbine
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Design Of Intake for High Release of Power
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Multi Jet Distributors for Pelton Wheels
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Discharge Distribution And Flow Energy Losses In
the Distributor
Q/QBEP
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• CFD Analysis of Free Jets Flows In Air

A Consultancy Project Sponsored By BHEL,
Bhopal 2008 -- 2009
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Governing Differential Equations

• 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,
  

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Arrangement of Jets
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CAD Model of Distributor
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Pelton Wheel Flow Distributor
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Static Pressure Distribution
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Distribution of Velocity Magnitude
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Exit Velocities
The area averaged values for the various critical
sections are listed below, Inlet 20.77
ms-1 Outlet 1 25.37 ms-1 Outlet 2 18.13
ms-1 Outlet 3 17.05 ms-1 Outlet 4 16.91
ms-1 Outlet 5 15.22 ms-1 Outlet 6 9.75 ms-1
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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.

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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

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A Complex Engineering Micro Alternate To Simple
Gigantic Natural System
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Flow Control using Spear Nozzle System
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Free Surface Expansion Shape for Maximum Power
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Simplification of Nozzle Shape
The nozzle and spear are perfectly streamlined to
reduce friction losses and achieve perfect
circular jets.
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Geometrical Relations for Nozzle
The values of a varies between 20 to 30 whereas
ß varies from 30 to 45.
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Industrial Correlations for Jet Area variation
with stroke
Optimal value of Outlet jet area, ao
s is the displacement of spear
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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
Then, the corresponding flow rate is
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Discharge Control using Spear Nozzle
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Linear Rate of Change Discharge w.r.t Stroke
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Geometrical Relations for Nozzle
2dO 2.4dO
dO
5dO 9dO
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Performance Analysis of Nozzle-Spear Valve
Ideal Nozzle-spear Valve
Along flow direction
Real Nozzle-spear Valve
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Pipe Material Absolute Roughness, e
Pipe Material micron(unless noted)
drawn brass 1.5
drawn copper 1.5
commercial steel 45
wrought iron 45
asphalted cast iron 120
galvanized iron 150
cast iron 260
wood stave 0.2 to 0.9 mm
concrete 0.3 to 3 mm
riveted steel 0.9 to 9 mm
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Numerical Computation of Total Pressure Variation
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Acceptable Performance of Nozzle
Jet carrying a discharge of Q to deliver a power P
To generate a discharge of Q, we need a least jet
diameter of
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The Diameter of Jet before Reaching Bucket
Diameter of the Jet at the outlet, do
It is important to find out the VC and outlet jet
diameters/areas