CFD Based Performance Analysis of Kaplan Turbine ... - IRNet Explore

ISBN: 978-93-81693-89-6
CFD Based Performance Analysis of Kaplan
Turbine for Micro Hydro Power
1 Alok Mishra, 2 R.P. 3 Saini, M.K. Singhal
1 PG Scholar, Alternate Hydro Energy Centre, Indian Institute of Technology, Roorkee, India;
2 Associate Professor, Alternate Hydro Energy Centre, Indian Institute of Technology, Roorkee, India;
3 Senior scientific Officer, Alternate Hydro Energy Centre, Indian Institute of Technology, Roorkee, India
1 mishra.alok10@gmail.com, 2 rajsafah@iitr.ernet.in, 3 mksalfah@iitr.ernet.in
Abstract: The conventional approach to assess turbine performance is its model testing which becomes costly and time
consuming. Model testing cannot be used for micro hydro range since cost is dominating factor for micro hydro projects.
Computational fluid dynamics(CFD) has becomes a cost effective tool for predicting the performance of turbine and also
for predicting detailed flow information inside the turbine to enable the selection of best operating condition. In the present
study, the simulation has been carried out for design and part load conditions at three different operating points..The
optimization of runner blade angle has been provided the part load efficiency of Kaplan turbine.
Keywords: Kaplan turbine; computational fluid dynamics(CFD); efficiency; wicket gate; runner blade.
1. INTRODUCTION
Demand of power increases day by day and supply of
power still not matches the demand so power sector is
reliable business. The demand for increasing the use of
renewable energy has risen over the last few years due to
environmental issues. The high emissions of greenhouse
gases have led to serious changes in the climate.
Although the higher usage of renewable energy would
not solve the problems over night, it is an important
move in the right direction. The most important
renewable sources are hydropower, biomass, geothermal,
solar and wind but technical, economic and
environmental benefits of hydroelectric power make it an
important contributor to the future world energy mix.
Hydropower contributes one-fifth of the world’s power
generation. In fact, it provides the majority of supply in
55 countries. For several countries, hydropower is the
only domestic energy resource. Its present role in
electricity generation is therefore substantially greater
than any other renewable energy technology [1].
The current concern on the global environment has
imposed a new sustain on the production of electricity.
The emphasis is put on development of environmental
friendly energies to promote the sustainable social
development. It is in these circumstances, the micro
hydro power is drawing more attention. A rural
population is scattered, poor and unaware of
technological progress. For such area, the isolation
micro-hydro power plants are usually the least-cost
option. This is mainly because other options for supply of
energy such as extension, diesel power, etc are more
expensive and difficult to install or operate in long run.
Since small water stream are usually available in the
most of the region, micro-hydro power plant can easily
meet the energy needs of small village or cluster of
settlements. The needs may be in the form of electricity or
motive power to be used for agro-processing, wood
working and for other small scale industries. This use of
electricity in form of heat can be contribute significantly
towards reducing the burning of wood and other biomass
, which has many derogatory implication in terms of
environmental and health. In addition to meet the needs of
an area, a properly designed, install and managed microhydro
power plant can also contribute significantly
towards employment generation, improved living
condition and improved education facilities.
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CFD Based Performance Analysis of Kaplan Turbine for Micro Hydro Power
Turbine is the main component of the hydro power
plant over all generation of the plant depends on the
performance of the hydro turbine. Investigation of flow
condition of hydro turbines is very important to know the
efficiency of the turbine. Model testing is generally
adopted to analyze the flow conditions. However this is
not economically viable especially for micro hydro
turbines. Further the part load efficiency of low head
turbines (Propeller) is considered to be poor. It is
therefore, there is need to develop a Kaplan runner for
micro hydro turbine, in order to improve the part load
efficiency. CFD becomes a powerful tool for
performance prediction on the hydro turbines, it consume
less time and cost for evaluation of performance of the
hydro turbine.
Drtina and Sallarberger [2] compared the
experimental data and 3D Euler and 3D Navier-stockes
result for the flow in Francis runner. Highlight the stateof-the-art
to predict the performance of Francis Turbine
by Numerical solution.
Prasad et al. [3] compared the efficiency of axial
flow turbine comes through experimental and CFD
analysis with three different guide vane angles.
Jain and Saini [4] predicted performance and
efficiency of Francis runner at 4 different operative
points of guide vane by using CFD and to validate the
same with model testing.
Kim et al. [5] predicted the performance of tubular
type hydro turbine for variable guide vane opening and
investigated influences of pressure, tangential and axial
velocity distributions on turbine performance by using
commercial CFD codes.
This paper present the CFD approach for prediction
of efficiency of 100 kW capacity Kaplan turbine. The
numerical simulations were carried out using commercial
CFD package Fluent in ANSYS 14 software for the
prediction of overall efficiency of Kaplan turbine. The
overall efficiency of hydro turbine was determined based
on the fundamental equations.
2. GEOMETRIC MODELING AND
SIMULATION
The CFD approach for efficiency prediction of 100 kW
capacity of Kaplan turbine with tubular casing is
presented. The rated head and discharge for the turbine
were 1.5 m and 7.03 m 3 /s respectively. The Kaplan
turbine consists casing, wicket gate, runner with blade
and daft tube. In the present study tubular casing were
taken. There are 14 wicket gate and 4 runner blades in
the model being analyzed. Models were created with the
help of Pro-e software. Blades of runner created in the
bladegen module of ANSYS 14 software and assemble
with hub in Pro-e software. The Assembly of
components of the Kaplan turbine are shown figure 1.
Figure 1. Assembly of Kaplan turbine
Meshing of components was carried out in mesh
module in ANASY-14 software. The mesh data of
different components of the turbine is shown in Table I
and the mesh models of the turbine are as given in figure
2, 3 & 4.
Component
Table I. Summery of mesh data
Tubular casing 754929
No. of Element
Wicket gate 1523396
Runner 486116
Figure 2. Meshed model of tubular casing with draft tube
The numerical analysis of turbine performance and
internal flow were carried out with the help of Fluent
module of ANSYS-14. Standard k-ε turbulence model
for single phase was used for the numerical simulation.
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CFD Based Performance Analysis of Kaplan Turbine for Micro Hydro Power
The simulations were carried out for design condition
and part load conditions with wicket gate openings at
75%, 65% and 55%. For each wicket gate opening four
simulations were carried out by varying runner blade
angle to optimize the efficiency. For Set of boundary
conditions mass flow rate was specified at casing inlet
and pressure outlet was specified at draft tube outlet.
Grid interface was defined between casing and runner as
well as between runner and wicket gate.
Figure 3. Meshed model of Wicket gate
The input parameters for calculating efficiency are as
given below;
a. Total pressure at turbine outlet(P t2 )
b. Discharge through turbine(Q)
c. the angular speed of the runner (ω)
The output parameters for calculating the efficiency are
shown below;
a. Total pressure at turbine inlet(P t1 )
b. The net torque acting on the runner(T)
3.1 Efficinecy for design condition
Simulation was carried out of the Kaplan turbine with
design parameters, which are the discharge is 7.03 m 3 /s
and head 1.5 m. For design condition wicket gate
opening is taken 85% i.e. 7.03 m 3 /s and the runner blade
angle is equal to the 18° at the outer distortion.
1. Input Parameters: The input parameters for the Fluent
are as given in Table II
Table II. Input parameter for fluent
Discharge, Q (m 3 /s)
Angular speed, ω
(rad/s)
Pressure at outlet
of Turbine, P t2 (Pa)
7.03 13.09 15092
Figure 4. Meshed model of Kaplan Runner
3. RESULT AND DISCUSSION
3.1 Computation efficiency of hydro turbine
The overall efficiency of a turbine with an
incompressible working fluid is defined as the ratio of
the work delivered to the rotor to the energy available
from the fluid stream. This ratio can be expressed as:
T ω
η
0
=
(1)
Q ( P t 1
− P t 2
)
Where, T is the net torque acting on the runner (N-m), ω
is the angular speed (radian), Q is discharge through
turbine (m3/s), P t1 is total pressure at the inlet to the
turbine and P t2 is the total pressure at the exit of the draft
tube.
2. Output Parameters: The output parameters generated
by the Fluent are as given in Table III
Pressure at inlet
of turbine, P t1
(Pa)
Table III. .Output parameter
Tx
(N-m)
136710.5 -33.38
Torque components
Ty
(N-m)
-
114.67
Tz
(N-m)
Torque, T
(N-m)
-59487.15 59487.27
The efficiency of the Kaplan turbine for design condition
has been found to be 91% from the Equation (1).
3.2 Pressure contour for design condtion.
The pressure variations obtained through the numerical
simulation are shown in the form of pressure contours.
The Pressure contours of turbine components are shown
in the figure 5. The total pressure variation is high near
the wall of the casing and runner. It is observed through
analysis that at inlet of the casing is maximum pressure.
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CFD Based Performance Analysis of Kaplan Turbine for Micro Hydro Power
gate opening increases as increasing the runner blade
angle and have maximum efficiency 85.38% at 20°
runner blade angle. The variation of efficiency with
runner blade for 65% opening is shown in figure 7.
Runner
Wicket gate
Efficiency
86
85
84
83
82
81
80
79
17 18 19 20 21 22
Runner Blade Angle
Figure 7. Variation of efficiency with runner blade angle
Tubular casing with daft tube
Figure 5. Contours of components of Kaplan turbine for
design condition
3.3 Efficiency at 75% wicket gate opening
Four different runner blade angles17°, 18°, 19° and 20°
has been used for four simulation of the Kaplan at 75%
of wicket gate opening. The efficiency for 75% wicket
gate opening increases as increasing the runner blade
angle and have maximum efficiency 90.41% at 19°
runner blade angle. The variation of efficiency with
runner blade is shown in figure 6.
Efficiency
91
90
89
88
87
86
85
84
16 17 18 19 20 21
Runner Blade angle
Figure 6. Variation of efficiency with runner blade angle
3.4 Efficiency at 65% wicket gate opening
Four different runner blade angles18°, 19°, 20° and 21°
has been used for four simulation of the Kaplan at 65%
of wicket gate opening. The efficiency for 65% wicket
3.5 Efficiency at 55% wicket gate opening
Four different runner blade angles19°, 20°, 21° and 22°
has been used for four simulation of the Kaplan at 55%
of wicket gate opening. The efficiency for 55% wicket
gate opening increases as increasing the runner blade
angle and have maximum efficiency 76.35% at 21°
runner blade angle. The variation of efficiency with
runner blade is shown in figure 8.
Efficiency
77
76
75
74
73
72
71
70
18 19 20 21 22 23
Runner Blade Angle
Figure 8. Variation of efficiency with runner blade angle
3.6 Efficiency curve for different operating conditions
The graph between efficiency and runner blade angle are
show in figure 9. The figure shows different wicket gate
opening curves which is shown by different colors. The
efficiency curve plot by joining efficiency of design
condition and the peak efficiencies of all part load
conditions.
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CFD Based Performance Analysis of Kaplan Turbine for Micro Hydro Power
Efficiency
93
91
89
87
85
83
81
79
77
75
73
71
69
67
65
16 17 18 19 20 21 22 23
Runner Blade angle
75% wicket gate opening
65% wicket gate opening
55% wicket gate opening
Part load efficiency curve
Figure 9.
Efficiency curve for different part load condition
4. CONCLUSION
In the present study, the operating parameters of the
Kaplan turbine have been optimized using commercial
CFD package ANSYS-14. The turbine having rated
capacity of 100 kW at rated head and discharge of 1.5 m
and 7.03 m3/s respectively. The simulation has been
carried out for three-dimensional with k- ε turbulence
model. Based on CFD analysis it has been found the total
pressure variation is high in runner and the wall of the
casing. In the casing inlet maximum value of total
pressure has been observed while minimum value of
pressure variation occurs at wicket gates as compare to
other components. The efficiency of the Kaplan tubular
turbine has been found to be maximum as 91% for design
condition i.e. at rated discharge 7.03m3/s and at rated
head 1.5 m at 85% wicket gate opening.
[2]. Drtina, P and Sallaberger, M “Hydraulic
turbines—basic principles and state-of-theart
computational fluid dynamics applications” Proc
Instn Mech Engrs Vol 213 Part C 1999
[3]. Prasad, V, Gahlot, V K & Krinnamachar, P “CFD
approach for design optimization and validation
for axial flow hydraulic turbine” Indian Journal of
Engineering & Material secince Vol. 16, August
2009,pp 229-236
[4]. Jain, S, Saini,R P & Kumar, A “CFD approach for
prediction of efficiency of Francis turbine”
IGHEM-2010, oct. 21-23, AHEC, IIT Roorkee,
India
[5]. Kim, Y T, Nam, S H, Cho, Y J, Hwang, Y, C,
Choi,Y D, Nam, C D & Lee, Y H “Tubular-Type
hydro turbine performance for variable guide vane
opening by CFD” The fifth international
conference on fluid mechanics, Aug 15-19,2007,
Shanghai, Chaina.
REFERENCES
[1]. Yukse, I “As a renewable energy hydropower for
sustainable development in Turkey” Renewable
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3219
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