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 flowsBut• 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

sinsinsinsinB

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

24 2

2

9.0Re74.5

7.3log

0625.0

hDk

fPipe Material Absolute Roughness, e

micron(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

gHKQd

vVCjet 2

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