International Journal of Engineering Trends and Technology (IJETT) – Volume 31 Number 3- January 2016
CFD Analysis of a Pelton Wheel
Gopal#1, Dr L Suresh Kumar*2, V Jaipal Reddy & V.Sandhya#3&4
#
1 Asst Prof., Chinthalapudi Engg College, Ponnur, Guntur, A.P, India.
*2, #3&4
Asst. Prof., C.B.I.T, Hyderabad, Telangana, India.
Abstract— In this paper, a Pelton Turbine was
being used to drive a pump to pump water. It was
required to be replace the Mild Steel buckets with
Aluminum alloy. The change in material will lead to
changes in the values of Displacements, Stress,
Strain, Max. Frequencies leading to resonance
which will cause the failure of the equipment. Hence
Static analysis and Modal analysis is to be done.
Also, the proposed material is also to be subjected
with a change in velocity of water striking the
buckets. Hence, a CFD analysis is also done. The
CFD analysis gives the changes in Pressures,
Temperature and the Mass flow rates. From these
analyses the Aluminum alloy is observed to be the
suitable material for the requirement.
Keywords — Pelton Wheel, CFD Analysis, Impulse
turbine, Iso efficiency curve, Runner angular
frequency.
I. Introduction
Types of Water turbines
Turbines convert fluid energy into
rotational mechanical energy. Based on the water
head conversion, the turbines may be classified
either as Reaction or Impulse turbines.
The head change leads to pressure drop,
when the fluid fills the blade passages in the runner
in a Reaction turbine.
The water head is converted into a high
velocity jet in a nozzle and the jet strikes the buckets,
in an Impulse turbine. The water is at a constant
pressure. Impulse turbines are ideally suited for high
heads and relatively low power.
The different types of water turbines used are the
following:
Pelton turbine - Impulse water turbine.
Francis turbine – Reaction water turbine.
Kaplan turbine – Variation of Francis
Turbine.
Turgo turbine- a modified form of the
Pelton wheel.
Cross-flow turbine, also known as BankiMichell turbine, or Ossberger turbine.
Fig. 1 Pelton Turbine parts
Pelton turbine - Lester Pelton (1829-1908), an
American inventor, has developed this turbine. The
Pelton turbine has spoon-shaped buckets which
harnesses the energy of falling water.
The Pelton turbine used in this experiment is an
impulse turbine. The Pelton turbine has water
coming out at a high velocity from the nozzle. The
high velocity jet strikes the buckets mounted on the
runner. The striking jet imparts momentum. The
buckets are shaped in a manner to divide the flow in
half and turn its relative velocity vector nearly 180°.
Computational Fluid Dynamics helps to analyze
the effects of the mass flow rates on the bucket. The
change in material with their properties are easily
analyzed with the software. The software aids to
analyze very minutely.
II. Working of Pelton Turbine
High speed water jets flows into the bucket
and the velocity changes when it flows as per the
contour of the bucket. The water exerts pressure on
the bucket on striking and loses its velocity as it
flows out side of the bucket. It flows out in an
opposite direction. This change of momentum in
water produces impulse and does work on the
turbine. Hence, a torque is generated which makes
the rotation of Pelton turbine shaft.
Optimum output is obtained when the blade
receives maximum impulse. This is obtained by
deflecting the water jet in a direction opposite of
striking the buckets. The relative speed with respect
to buckets should be same.
The water jet velocity should be twice the
bucket’s velocity. This will provide maximum
power and efficiency. A very small percentage of the
water's original kinetic energy will still remain in the
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International Journal of Engineering Trends and Technology (IJETT) – Volume 31 Number 3- January 2016
water. This allows the bucket to be emptied at the
same rate at which it is filled. This allows the water
flow to continue uninterrupted.
The efficiency of the turbine is provided
from isoefficiency curves. They show the
interrelationship among Q, w, and h.
The balancing of the side load forces on the
wheel and the smooth and efficient momentum
transfer to the turbine wheel is done by placing two
buckets side-by-side. A splitter separates the two
buckets. The high velocity water jet is made to strike
the splitters which make the water jet in half.
The Pelton wheels have one stage only as
all of the available energy is extracted in the first
stage itself.
Fig. 3 Iso Efficiency Curves
A typical iso efficiency plot for a
laboratory-scale Pelton turbine.
Under ideal conditions the maximum
power generated is about 85%, but experimental data
shows that Pelton turbine are somewhat less efficient
(approximately 80%) due to windage, mechanical
friction, back splashing, and non uniform bucket
flow.
Fig 2. Schematic of an impulse turbine
The power extracted from the available head by the
turbine is given by :
Where Q is the discharge of the incoming jet, P is
the Power and Havailable is the available pressure
head on the nozzle.
The primary feature of the impulse turbine
is the power production as the jet is deflected by the
moving buckets. It is assumed that the speed of the
exiting jet is zero negligible head loss at the nozzle
and at the impact with the buckets.
By applying the angular momentum equation
(assuming negligible angular momentum for the
exiting jet) to the same control volume about the
axis of the turbine shaft the absolute value of the
power developed by the turbine can be written as
Where w is the angular velocity of the runner, T is
the torque acting on the turbine shaft, and N is the
rotational speed of the runner.
The efficiency of the turbine is defined
as the ratio between the powers developed by the
turbine to the available water power
III. Experimental Procedure
Measurements are taken to determine the efficiencyrotational curve for two discharges as per the
sequence described below:
1. Close the two drain valves positioned on the
releasing basin.
2. Open the discharge controlling valve on the inlet
pipe and record the pressure on the pressure gage.
3. Loosen the torque brake so that there is no friction
applied on the turbine shaft. Adjust the torque gauge
display to zero reading. For this setting the
tachometer should read a rotational speed of about
1800 rpm.
4. After the water level in the basin has become
steady, measure the head on the weir using the point
gauge located on the basin.
5. Measure the rotational speed of the shaft with no
torque resistance on the shaft (runaway condition)
with the provided tachometer. Carefully align the
tachometer reading line perpendicular to the
phosphorescent tape on the shaft.
6. Tighten slightly the friction hand-wheels and
record the torque displayed on the friction gauge as
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well as the rotational speed of the shaft with the
tachometer.
4. ANSYS is used for doing the finite element
analysis.
Repeat this step until approximately 10 different
settings are obtained with the last setting with the
turbine stopped.
5. Structural Analysis and Modal Analysis is done
for Mild Steel and Aluminium Alloys.
7. After the shaft is fully stopped, completely loosen
the torque brake and zero the friction gauge.
8. Increase discharge by opening the pipe inlet valve
to a runaway speed of 2000 rpm and repeat steps 2
through 7.
6. Fluid Flow Analysis is done by the
ANSYS/FLOTRAN CFD (Computational Fluid
Dynamics). This offers comprehensive tools for
analyzing two-dimensional and three-dimensional
fluid flow fields.
9. Open drain valves and allow the basin to drain
until only a trickle of water flows over the weir.
Wait for weir flow to stop, then measure the water
depth indicated by the point gauge.
IV. Calculations of Pelton wheel
turbine
Load on turbine
P = η (1-cosβ) πDR2 /16 (2gh/ (1+ξ+λL/Dr (Di4
/Dp4))3/2
=0.85×(1-COS1700)π
(1.5)2/16[2×9.81×670/1+8.854+1.4× (6000/1.5) ×
(0.184/14)]3/2
Fig. 4 Model of the Pelton Wheel
A. STRUCTURAL ANALYSIS OF PELTON
WHEEL
For MILD STEEL
=0.85×(1.984)×(7.068/16× (13.63)
=10.153 KN
Pressure = load/ area
=10.153/801=1.269125×10 -3KN/mm2
Runner angular frequency
ω = 1/2R [2gh/1+ξ+λ(L/DR)X(Di4/Dp4)]
=
(1/1.5)[2x9.81x670/1+8.854+(6000/1.5)x(0.18 4/1
=1/1.5[835.548]
= 557.032 Hz
Torque acting on runner
T=p/ω
= 10.153/557.032
=0.01822Nmm
Fig. 5 Imported Model from Pro/Engineer
Table 1 : Element details
Element Type: Solid 20 node 95
Material Properties:
Youngs Modulus (EX) : 205000N/mm2
Poissons Ratio (PRXY) : 0.29
Density
:0.0000075kg/mm3
V. Analyses of the Pelton Wheel
1. Pro/ENGINEER Wildfire is used to create 3D
design.
2. Create the mesh and assign the material and
structural properties.
3. Apply the boundary conditions.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 31 Number 3- January 2016
B. MODAL ANALYSIS
Fig. 6 Meshed Model
At loads - Pressure – 0.044N/mm2
For ALLUMINUM ALLOY
Table 2 : Element Details
Element Type: Solid 20 node 95
Material Properties:
Youngs Modulus (EX) : 68900N/mm2
Poissons Ratio (PRXY) : 0.29
Density
:0.0000027kg/mm3
Meshed Model
Fig. 7 Displacement Vector
Fig. 10 At Loads - Pressure – 0.044N/mm2
Fig. 8 Stress – Von Mises Stress
Fig. 11 Displacement Vector Sum
Fig.9. Total strain-von misses total strain
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Fig. 12 Stress – Von Mises Stress
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International Journal of Engineering Trends and Technology (IJETT) – Volume 31 Number 3- January 2016
Fig. 17 Tempertaure
Fig. 13 Total strain-von misses total strain
Table 3: Mass flow rate – (kg/s)
Inlet
59.05997
Outlet
-59.082977
Net
-0.023006439
AT VELOCITY- 8 m/s
MODAL ANALYSIS
C. CFD ANALYSIS OF PELTON WHEEL
BLADE
AT VELOCITY-4.42m/s
Fig. 18 Static pressure
Fig. 14 Bucket profile
Fig. 19 Velocity magnitude
Fig. 15 Static Pressure
Fig. 20 Tempertaure
Table 4 : Mass flow rate – (kg/s)
Inlet
106.89588
Outlet
-106.94014
Net
-0.04425811
Fig. 16 Velocity magnitude
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International Journal of Engineering Trends and Technology (IJETT) – Volume 31 Number 3- January 2016
increased by 2% and mass flow rate is increased by
18%.
RESULTS TABLE
A. Table 5: STRUCTURAL ANALYSIS
MATE-
DISPLACE
RIAL
MENT
STRESS
STRAIN
2
(N/mm )
So it can be concluded that using aluminum alloy is
better.
(mm)
MILD
0.001332
0.871122
0.430E-05
0.00298
0.720
0.105 E-04
STEEL
1.
ALUMINU
M ALLOY
B. Table 6 : MODAL ANALYSIS
Mode
Mild
Al Alloy
Steel
1
0.299579
0.34
Frequency (Hz)
23.7436
18.0095
Displacement
0.254628
0.341102
Frequency (Hz)
26.333
18.06
Displacement
0.224883
0.243
32.076
23.8426
Displacement
(mm)
2
(mm)
3
References
(mm)
Frequency (Hz)
C. Table 7 : CFD ANALYSIS
Veloc Pressu Velo
Tem
ity
re
City
pera
(m/s)
(N/m
(m/s) ture
m2)
(K)
4.42
4.67e+0 7.40
305
Mass flow
Rate
(Kg/sec)
Flow Analysis Inside a Pelton Turbine Bucket by B.
Zoppé, C. Pellone, T. Maitre and P. Leroy.
2. Some Aspects of Performance Improvement of Pelton
Wheel Turbine with Reengineered Blade and Auxiliary
Attachments by Suraj Yadav.
3. Victor L. Streeter and E. Benjamin Wylie (1981), Fluid
Mechanics, McGraw-Hill Book Company New York.
4. Irving H. Shames (1992), Mechanics of Fluids, McGraw
Hill International Edition.
5. Robert L. Daugherty, Joseph B. Franzini, E. John
Finnemore (1989), Fluid Mechanics with Engineering
Applications, McGraw-Hill Book Company, New York.
6. W.A.Doble (1899), ―The Tangential Water Wheel‖,
Transaction of the American Institute of Mining Engineers,
Vol. 29, pp.852-858.
7. W Malalasekera and H K Versteeg (1995), ―An Introduction
to Computational Fluid Dynamics‖, the Finite Volume
Method, Longman.
8. W.N. Dawes (1998), ―Computational Fluid Dynamics for
Turbomachinery Design‖, Whittle Laboratory, Department
of Engineering, University of Cambridge, UK.
9. B. Zoppe, C. Pellone, T. Maitre, P. Leroy (2006), ―Flow
Analysis Inside a Pelton Turbine Bucket‖, Transaction of
ASME, Vol. 128, pp.500-511.
10. Zn Zhang , M Casey (2008), ―Experimental Studies of the
jet of a Pelton Turbine‖, Power and Energy , Mech E Vol.
221 Part A, pp.1181-1189.
11. Bansal R.K. (2005), ―A textbook of Fluid Mechanics and
Hydraulic Machines‖, Laxmi Publications, New Delhi.
12. Shamesw I.H. (2002), ―Mechanics of Fluids‖, McGraw Hill
Publications [16] Roer E.A. Arndt (2005), ―Hydroelectric
Power Stations‖, Encyclopaedia of Physical Science and
Technology.
0.023006439
4
8.0
1.53e+0
13.4
305
0.04425811
5
CONCLUSION
In this project, a Pelton Turbine was
analyzed to find out the effects of replacing the
existing Mild Steel buckets with Aluminum alloy.
Modeling is done in Pro/Engineer. Structural, modal
and CFD analysis on the Pelton wheel in Ansys.
By observing the structural analysis results,
the analyzed stress values are less than the allowable
stress values for Aluminum alloy.
In the modal analysis results, the
frequencies are less than steel, vibrations are less
when aluminum alloy is used.
CFD analysis is done for different
velocities at 4.42 m/s and 8 m/s. From the analysis,
the velocity is increased by 81%, pressure is
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