finite element analysis and experimental investigations on small size wind turbine blades
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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
493
FINITE ELEMENT ANALYSIS AND EXPERIMENTAL
INVESTIGATIONS ON SMALL SIZE WIND TURBINE BLADES
T.Vishnuvardhan, Associate Professor, Intell Engineering College,
Anantapur.A.P
Dr.B.Durga Prasad, Associate Professor, JNT University,
Anantapur.A.P
ABSTRACT
The demand for Small / Micro Wind Turbines is increasing worldwide and the basic
advantage of using small size wind turbines is the production of power at low wind speeds.
The electricity produced by wind power is cost effective when compared with remaining
green energy sources. Small wind turbine systems can be easily installed near the site where
the power is required thus the investment on power transmission lines can be reduced. The
paper presents the development of small wind turbine blade models in two different profiles
R21 and R22. NACA 63-415 airfoil is used for the development of blades. The blades are
developed and fabricated for one kW wind turbine generator system. Finite element analysis
was conducted by varying the composition of materials used for blade fabrication.
Experimental investigations through load deflection test and cyclic load bench test conducted
on six blade varieties. The results show the degradation of material properties as the
experiment is getting progressed. Finally a better performing blade was identified from the
result obtained from FEA, load deflection test and cyclic load bench test.
Key Words: Small Wind Turbine – Blade Profiles – Load Deflection Test - Cyclic Load
Bench Test.
1. INTRODUCTION
Most small / micro size wind turbines are developed to produce power at the locations
where the availability of wind at low speeds. Most of the small wind turbines use permanent
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 3, Issue 3, September - December (2012), pp. 493-503 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2012): 3.8071 (Calculated by GISI) www.jifactor.com
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© I A E M E
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
494
magnet alternators which are simplest and robust generator configurations. As the wind
turbine size decreases the rotor speed increases and the power extraction will be more based
on the wind velocity parameter. The blades on the rotor experience a high number of flexing
cycles which impacts their life. The aerodynamics, material properties are the key factors in
identifying a better performing blade model. The following sections deal with profile
development, FEA and experimental investigations on small size wind turbine blades with
different profiles.
2. BLADE PROFILE DEVELOPMENT
The present paper focuses on the development of small wind turbine blades
developed from R21 and R22 profiles using a specified design methodology for small size
horizontal axis wind turbine systems. NACA 63-415 airfoil is used to develop the wind
turbine blades in R21 and R22 profiles. The investigations are carried out by varying the
material compositions used for blade development. The following are the materials used for
fabrication of wind turbine blades. i) Glass fiber reinforced with polyester resin ii) Glass
fiber reinforced with polyester resin sandwiched with UV hard foam and iii) Glass fiber
reinforced with Epoxy resin sandwiched with UV hard foam. UV hard foam is used as a
central beam, which increases the stiffness properties of the blade [1]. NACA 63-415 airfoil
shape used for the development of blade profiles is shown in the Figure 1. The
corresponding station and ordinate values for both upper and lower surfaces are shown in
Table 1.
Table 1 Stations Values along with Ordinates NACA 63-415
Upper Surface Values Lower Surface Values
Station Ordinate Station Ordinate
0 0 0 0
0.3 1.2870 0.7 -1.0870
0.5249 1.5889 0.9755 -1.3075
0.9927 2.0677 1.5081 -1.6398
2.1990 2.9571 2.8019 -2.2126
4.6599 4.2652 5.3409 -3.0019
7.1476 5.2629 7.8580 -3.5669
9.6477 6.0757 10.3528 -4.0065
14.6689 7.3487 15.3318 -4.6579
19.7051 8.2802 20.2963 -5.0952
24.7506 8.9388 25.2582 -5.3595
29.8051 9.3651 30.2011 -5.4759
34.8529 9.5591 35.1484 -5.4373
39.9049 9.5279 40.0957 -5.2435
44.9547 9.2891 45.0453 -4.9083
50 8.8704 50 -4.4576
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
495
55.0398 8.2975 54.9618 -3.9167
60.0704 7.5947 59.9296 -3.3102
65.0937 6.7793 64.9070 -2.6576
70.1060 5.8748 69.8949 -1.9859
75.1089 4.9056 74.8911 -1.3257
80.1017 3.8978 79.8983 -0.7122
85.0848 2.8821 84.9152 -0.1918
90.0595 1.8851 89.9405 0.1844
95.0289 0.9336 94.9721 0.3309
100 0 100 0
L.E. Radius = 1.473 percent c
Slope of Mean Line at LE = 0.1685
0 2 0 4 0 6 0 8 0 1 0 0
- 6
- 4
- 2
0
2
4
6
8
1 0
Air
foil O
rdin
ate
s
A i r f o i l S t a t i o n s
U p p e r S u r f a c e V a l u e s
L o w e r S u r f a c e V a l u e s
Fig: 1 NACA 63-415 Airfoil Upper and Lower Surfaces
developed from Ordinates and Stations
3. FINITE ELEMENT ANALYSIS OF SMALL WIND TURBINE BLADES
Finite element analysis is carried out for all blade varieties to extract the behavior of
the blades when they are subjected to loading. The solid models of R21 and R22 blade
varieties are developed in pro/engineer software and they are shown in Figures 2 & 3.
Using ANSYS static analysis was carried out and the Vonmises stresses and
corresponding blade deformations are calculated. Figure 4 and 5 shows the values of
displacement and Vonmises stresses corresponding to SWT blade from R22 profile, GFRP
with epoxy resin UV sandwiched material.
The vibration characteristics of the blades are analyzed by performing modal
analysis. Further the excitation forces on the blades caused by the stochastic wind loads are
imposed on the rotor model and the stable response of the system is calculated by harmonic
analysis. Mode shapes developed for R22 GFRP + Epoxy + SW are shown in Figures 6, 7,
8, 9 and 10. Harmonic analysis results for the same blade are shown in Figures 11, 12, 13,
14, 15 and 16. Tables 2, 3, 4, 5, 6 and 7 show the frequency values for different modes for
all blade varieties.
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
496
Fig: 2 R21 SWT Blade Assembly
Fig: 3 R22 SWT Blade Assembly
Fig:4 Static Analysis of R-22- GFRP + Epoxy + SW
Blade - at 0.02450 N/mm2 Wind Pressure - Displacement
Fig:5 Static Analysis of R-22- GFRP + Epoxy +
SW Blade - at 0.02450 N/mm2 Wind Pressure -
Vonmises Stress
Fig:6 Modal Analysis of R-22- GFRP + Epoxy + SW
Blade – I Mode
Fig:7 Modal Analysis of R-22- GFRP + Epoxy +
SW Blade – II Mode
Fig:8 Modal Analysis of R-22- GFRP + Epoxy + SW
Blade – III Mode
Fig:9 Modal Analysis of R-22- GFRP + Epoxy +
SW Blade – IV Mode
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
497
Fig:10 Modal Analysis of R-22- GFRP + Epoxy + SW Blade – V
Mode
Fig: 11 Harmonic Analysis of R-22- GFRP + Epoxy +
SW Blade – Root– at 0.02450 N/mm2 Wind Pressure
- Displacement
Fig: 12 Harmonic Analysis of R-22- GFRP + Epoxy + SW Blade
– Mid – at 0.02450 N/mm2 Wind Pressure - Displacement
Fig: 13 Harmonic Analysis of R-22- GFRP + Epoxy +
SW Blade – Tip– at 0.02450 N/mm2 Wind Pressure -
Displacement
Fig: 14 Harmonic Analysis of R-22- GFRP + Epoxy + SW Blade
– Root– at 0.02450 N/mm2 Wind Pressure - Vonmises Stress
Fig: 15 Harmonic Analysis of R-22- GFRP + Epoxy +
SW Blade – Mid – at 0.02450 N/mm2 Wind Pressure
- Vonmises Stress
Fig: 16 Harmonic Analysis of R-22- GFRP + Epoxy + SW Blade
– Tip– at 0.02450 N/mm2 Wind Pressure - Vonmises Stress
Fig: 17 Partial Deflection of the Blade
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
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Fig: 20 Failure at the Root of Blade in Cyclic
Load Test
-10 0 10 20 30 40 50 60 70
0
100
200
300
400
500
600 Load D eflection Tes t
Load App lied a t T IP
B lade Pro file - R 22
Materia l - GFRP+EPO XY+ SW
De
flection
in
'mm
'
Load in 'Kgs'
T ip
M id
Root
Fig:21 Load Deflection Test - R-22 - GFRP +
Epoxy + SW Blade – Load Applied at Tip
-10 0 10 20 30 40 50 60 70 80
0
20
40
60
80
100
120
140
160
180
Load in 'Kgs'
Load Deflection Test
Load Applied at MID
Blade Profile - R22
Material - GFRP+EPOXY+ SW
De
flection
in
'mm
'
T ip
Mid
Root
Fig:22 Load Deflection Test - R-22 - GFRP +
Epoxy + SW Blade – Load Applied at Mid
0 20 40 60 80
0
10
20
30
40
50 Load Deflection Test
Load Applied at ROOT
Blade Profile - R22
Material - GFRP+Polyester + SW
De
flection
in
'mm
'
Load in 'Kgs'
T ip
M id
Root
Fig:23 Load Deflection Test - R-22 - GFRP +
Epoxy + SW Blade – Load Applied at Root
4. LOAD DEFLECTION TEST
The moments, thrust torque and power on the rotor can be produced from the various
forces that cause loads on the small wind turbine rotor system are aerodynamic forces,
centrifugal forces and gravitational forces. For small wind turbine rotors aimed to produce
the power approximately 1 kW, their blades which actually experience these forces are to be
tested for their ability in withstanding them. The turbine blades can be tested for their
ultimate strength by conducting load deflection test. A fixture setup is constructed, to hold
the blade at its root section.
Fig: 18 Cyclic Load of 15 Kg. Applied on the
Blade
Fig:19 Cyclic Load of 25 Kg. Applied on the
Blade
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
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Table 2 R21 GFRP + Polyester Solid Blade - MODE Frequency Values
Sno Mode Frequency (Hz)
1 I 23.607
2 II 100.775
3 III 110.642
4 IV 233.534
5 V 300.236
Table 3 R21 - GFRP + Polyester + SW - MODE Frequency Values
Sno Mode Frequency (Hz)
1 I 24.801
2 II 105.709
3 III 115.140
4 IV 243.166
5 V 311.784
Table 4 R21 GFRP + Epoxy + SW - MODE Frequency Values
Sno Mode Frequency (Hz)
1 I 25.134
2 II 107.128
3 III 116.686
4 IV 246.430
5 V 315.969
Table 5 R22 GFRP + Polyester Solid Blade - MODE Frequency Values
Sno Mode Frequency (Hz)
1 I 17.471
2 II 72.585
3 III 83.156
4 IV 187.266
5 V 259.289
Table 6 R22 GFRP + Polyester + SW - MODE Frequency Values
Sno Mode Frequency (Hz)
1 I 22.051
2 II 91.441
3 III 104.551
4 IV 235.532
5 V 323.911
Table 7 R22 GFRP + Epoxy + SW - MODE Frequency Values
Sno Mode Frequency (Hz)
1 I 22.437
2 II 93.043
3 III 106.381
4 IV 239.661
5 V 329.595
The blade resembles a cantilever beam when it is fixed, critical sections are
identified on which the load is to be applied and corresponding deflections are measured.
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
500
The three critical sections are at tip, middle and root. The experiment is conducted for all
blade varieties and it contains three phases initially the load is applied at tip of the blade,
deflections are measured at tip, mid and root. In the second phase the load is applied at mid
section and the deflection is measured at tip, mid and root. In the final phase the load is
applied at root and the deflection is measured at three locations. The load is increased with a
unit value from 0 Kgs, and is continued till the blade fails. The experimental setup showing
the partial deflection of the blade when the load is applied at the tip is represented in Figure
17. Table 8 show the measured distances for R21 and R22 profile blades at which the load
should be applied and the deflections are to be measured.
Table 8 Distance Measurement from Fixed End to Critical Sections Sno Blade
Profile
Distance from the fixed
end to Root Section
Distance from the fixed
end to Mid Section
Distance from the fixed
end to Tip Section
1 R21 150 mm 610 mm 950 mm
2 R22 200 mm 660 mm 1030 mm
The load deflection test results for R22 profile blade produced from GFRP + Epoxy +
SW material are represented in Figures 21, 22 and 23.
5. CYCLIC LOAD BENCH TEST
A wind turbine blade is subjected during life time a large number of dynamic loads
produced by the rotation and turbulent nature of wind on blades[3]. Fatigue comes in to
picture for wind turbine blades as they are subjected to cyclic loading. These loading cause
failures of blade like cracks and rupture and it is very much essential to identify the fatigue
behavior of the wind turbine blades [7,8] .
As there is no standard procedure for determining the spectrum loads on small wind
turbines, cyclic load bench test was developed to understand the behavior of the blade based
on the failures by causing strain on the blades[6]. The cyclic load bench test setup is shown
in the Figures 18 and 19.
5.1 Cyclic Load Test Procedure
The bench can be used for small wind turbine blades with a maximum length of 1.5
meters. The test bench is having a load cell located at the top portion of the setup. A fixture
is also developed for holding the blade at its root section and the blade is instrumented with
strain gauges to measure the deformation. In the test a cyclic load will be applied on the
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
501
blades with constant number of cycles (30000) and the load which is applied on the blade
will be further increased once the blade can withstand the cyclic loads.
The test procedure is performed based on “constant cycles-incremental load-strain
measurement”, will be continued till the crack or any other failure occurs. The strain
measurement is carried out after the completion of prescribed number of cycles at each
magnitude of load applied on the blade. The experimental results are shown in Figures 24,
25, 26, 27, 28 and 29.
0 5000 10000 15000 20000 25000 30000
-6
-5
-4
-3
-2
-1
0
1 C yclic Load - D e flection T esti - R 21-
G F R P + P olys te r S o lid B lade
De
flection in 'm
m'
N um ber of C yc les
3 K g . 6 K g .
9 K g .
12 K g.
15 K g.
Fig.24 Cyclic Load Test Results of R-21 –
GFRP + Polyester Solid Blade
0 5 0 0 0 1 0 0 0 0 1 5 0 0 0 2 0 0 0 0 2 5 0 0 0 3 0 0 0 0
-6
-5
-4
-3
-2
-1
0
1 C y c l ic L o a d - D e f le c t io n T e s t i - R 2 2 -
G F R P + P o ly s te r S o lid B la d e
Deflection
in 'm
m'
N u m b e r o f C yc le s
3 K g .
6 K g . 9 K g .
1 2 K g .
1 5 K g .
Fig.25 Cyclic Load Test Results of R-22 –
GFRP + Polyester Solid Blade
0 5 0 0 0 1 0 0 0 0 1 5 0 0 0 2 0 0 0 0 2 5 0 0 0 3 0 0 0 0
-4 .5
-4 .0
-3 .5
-3 .0
-2 .5
-2 .0
-1 .5
-1 .0
-0 .5
0 .0
0 .5
1 .0 C y c lic L o a d - D e f le c t io n T e s t i - R 2 1 -
G F R P + P o ly s te r + S W B la d e
De
flection in 'm
m'
N u m b e r o f C yc le s
3 K g . 6 K g .
9 K g . 1 2 K g . 1 5 K g .
Fig.26 Cyclic Load Test Results of R-21 –
GFRP + Polyester + SW Blade
0 5 0 0 0 1 0 0 0 0 1 5 0 0 0 2 0 0 0 0 2 5 0 0 0 3 0 0 0 0
- 6
- 5
- 4
- 3
- 2
- 1
0
1 C y c lic L o a d - D e f le c t io n T e s t i - R 2 2 -
G F R P + P o ly s te r + S W B la d e
De
flection in 'm
m'
N u m b e r o f C y c le s
3 K g . 6 K g . 9 K g .
1 2 K g . 1 5 K g . 1 8 K g .
Fig.27 Cyclic Load Test Results of R-22 –
GFRP + Polyester + SW Blade
0 5 00 0 10 00 0 1 50 00 200 00 2 50 00 3 00 00
-1 8
-1 6
-1 4
-1 2
-1 0
-8
-6
-4
-2
0
2C yc lic L oa d - D e flec tio n T es ti - R 2 1 - G F R P + E p o x y + S W B la d e
De
fle
ctio
n in
'mm
'
N u m ber o f C ycles
3 K g. 6 K g.
9 K g. 1 2 K g .
1 5 K g .
1 8 K g . 2 1 K g .
Fig.28 Cyclic Load Test Results of R-21 –
GFRP + Epoxy + SW Blade
0 5 0 0 0 1 0 0 0 0 1 5 0 0 0 2 0 0 0 0 2 5 0 0 0 3 0 0 0 0
-1 7
-1 6
-1 5
-1 4
-1 3
-1 2
-1 1
-1 0
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
C y c lic L o a d - D e fle c t io n T e s ti - R 2 2 - G F R P + E p o x y + S W B la d e
De
fle
ctio
n in
'mm
'
N u m b e r o f C yc le s
3 K g .
6 K g . 9 K g .
1 2 K g .
1 5 K g . 1 8 K g .
2 1 K g . 2 5 K g .
Fig.29 Cyclic Load Test Results of R-22 –
GFRP + Epoxy + SW Blade
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
502
CONCLUSIONS
The paper shows a specific methodology to determine the load deflection
characteristics and the cyclic load behavior of small wind turbine blades. The following are
some of the important conclusions drawn from the experiments
� All the blades are capable to bear maximum loading value when applied at the root
section and the blades will fail at lower magnitude of loading, when the load is
applied at tip of the blade.
� It is observed that all the blades when subjected to loading irrespective of the location
at which the load is applied, the failure crack is observed near the root of the blade.
The blade tends to fail by creating a crackling sound.
� When the load deflection test results are compared for all varieties, the R22 profile
blade produced from GFRP + Epoxy + SW is showing more structural strength.
Even in R21 profile also the produced from the same material is showing more
structural strength.
� In cyclic load bench test, the GFRP + Epoxy + SW blades have shown a better
performance in both R21 and R22 blade profiles. Out of all the six varieties of blades
R22 profiled based blade fabricated from GFRP + Epoxy +| SW has shown the
leading performance by with standing a cyclic load of 25 Kgs. with a deflection of
16mm below the reference point, at 30000 cycles.
� In R21 profile, the blade fabricated from GFRP + Epoxy +| SW has shown the
leading performance by with standing a cyclic load of 21 Kgs with a deflection of
16.75 mm below the reference point, at 30000 cycles.
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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
503
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