Finite element analysis and experimental investigations

INTERNATIONALMechanical Engineering and Technology (IJMET), ISSN 0976 –
International Journal of JOURNAL OF MECHANICAL ENGINEERING
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
AND TECHNOLOGY (IJMET)

ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
IJMET
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)
©IAEME
www.jifactor.com

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

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –

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

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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

U p p e r S u r f a c e V a lu e s
L o w e r S u r f a c e V a lu e s

10
Airfoil Ordinates

8

6

4

2

0

-2

-4

-6
0 20 40 60 80 100

A ir fo il S t a tio n 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.

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Fig: 2 R21 SWT Blade Assembly Fig: 3 R22 SWT Blade Assembly

Fig:4 Static Analysis of R-22- GFRP + Epoxy + SW Fig:5 Static Analysis of R-22- GFRP + Epoxy +
Blade - at 0.02450 N/mm2 Wind Pressure - Displacement SW Blade - at 0.02450 N/mm2 Wind Pressure -
Vonmises Stress

Fig:6 Modal Analysis of R-22- GFRP + Epoxy + SW Fig:7 Modal Analysis of R-22- GFRP + Epoxy +
Blade – I Mode SW Blade – II Mode

Fig:8 Modal Analysis of R-22- GFRP + Epoxy + SW Fig:9 Modal Analysis of R-22- GFRP + Epoxy +
Blade – III Mode SW Blade – IV Mode

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Fig:10 Modal Analysis of R-22- GFRP + Epoxy + SW Blade – V Fig: 11 Harmonic Analysis of R-22- GFRP + Epoxy +
Mode SW Blade – Root– at 0.02450 N/mm2 Wind Pressure
- Displacement

Fig: 13 Harmonic Analysis of R-22- GFRP + Epoxy +
Fig: 12 Harmonic Analysis of R-22- GFRP + Epoxy + SW Blade SW Blade – Tip– at 0.02450 N/mm2 Wind Pressure -
– Mid – at 0.02450 N/mm2 Wind Pressure - Displacement Displacement

Fig: 14 Harmonic Analysis of R-22- GFRP + Epoxy + SW Blade Fig: 15 Harmonic Analysis of R-22- GFRP + Epoxy +
– Root– at 0.02450 N/mm2 Wind Pressure - Vonmises Stress SW Blade – Mid – at 0.02450 N/mm2 Wind Pressure
- Vonmises Stress

Fig: 16 Harmonic Analysis of R-22- GFRP + Epoxy + SW Blade Fig: 17 Partial Deflection of the Blade
– Tip– at 0.02450 N/mm2 Wind Pressure - Vonmises Stress

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Fig: 18 Cyclic Load of 15 Kg. Applied on the
Fig:19 Cyclic Load of 25 Kg. Applied on the
Blade Blade

600 Lo ad D eflectio n T es t
Lo ad A pp lied a t T IP
B la de P ro file - R 22
500 M a te ria l - G F R P + E P O X Y+ S W

400

Deflection in 'mm'
300

200

100
T ip
M id
0
R o ot

-10 0 10 20 30 40 50 60 70
Lo a d in 'K g s'

Fig: 20 Failure at the Root of Blade in Cyclic
Fig:21 Load Deflection Test - R-22 - GFRP +
Load Test
Epoxy + SW Blade – Load Applied at Tip
180 50 Load D eflection Test
Load D eflection Test
Load Applied at MID Load Applied at RO O T
160
Blade Profile - R 22 Blade Profile - R 22
Material - G FR P+EPO XY+ SW 40 M aterial - G FR P+Polyester + SW
140

120
30
Deflection in 'mm'

Deflection in 'mm'

100

80
20

60

40 10

20 Tip T ip
Mid M id
0
0 Root R oot

-10 0 10 20 30 40 50 60 70 80 0 20 40 60 80
Load in 'Kgs' Load in 'K gs'

Fig:22 Load Deflection Test - R-22 - GFRP + Fig:23 Load Deflection Test - R-22 - GFRP +
Epoxy + SW Blade – Load Applied at Mid 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.

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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
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
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
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
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
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.

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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 Distance from the fixed Distance from the fixed Distance from the fixed
Profile end to Root Section end to Mid Section 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

500


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.

1 C y clic L o a d - D e fle ctio n T e sti - R 2 1 - 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 lys te r S o lid B la d e G F R P + P o ly s te r S o lid B la d e

0 0

-1 -1

Deflection in 'mm'
Deflection in 'mm'

-2
-2

-3
-3

-4
-4
3 Kg. 3 K g.
6 Kg. -5 6 K g.
-5 9 Kg. 9 K g.
1 2 K g. 12 K g.
-6
1 5 K g. 15 K g.
-6
0 50 0 0 1 0 00 0 1 50 0 0 2 00 0 0 25 0 00 3 00 0 0 0 5000 10000 15000 20000 25000 30000
N u m b er of C yc le s N u m b e r o f C y c le s

Fig.24 Cyclic Load Test Results of R-21 – Fig.25 Cyclic Load Test Results of R-22 –
GFRP + Polyester Solid Blade GFRP + Polyester Solid Blade
1 .0 C y c lic L o a d - D e fle c tio n T e s ti - R 2 1 - 1 C y c li c L o a d - D e f l e c t i o 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 G F R P + P o ly s te r + S W B la d e
0 .5
0
0 .0

- 0 .5 -1

- 1 .0
Deflection in 'mm'

Deflection in 'mm'

-2
- 1 .5

- 2 .0 -3
- 2 .5
-4
- 3 .0 3 K g.
3 K g. 6 K g.
- 3 .5 6 K g. -5 9 K g.
9 K g. 12 Kg.
- 4 .0
12 K g. 15 Kg.
15 K g. -6
- 4 .5 18 Kg.

0 5000 10000 15000 20000 25000 30000 0 5000 10000 15000 20000 25000 30000
N u m b e r o f C y c le s N u m b e r o f C y c le s

GFRP + Polyester + SW Blade GFRP + Polyester + SW Blade
C y c lic L o a d - D e fle c tio n T e s ti - R 2 1 - C y c lic L o a d - D e fle c tio n T e s ti - R 2 2 -
2
G F R P + E p o x y + S W B la d e 1
G F R P + E p o x y + S W B la d e
0 0
-1
-2 -2
-3
-4 -4
-5
-6 -6
Deflection in 'mm'

Deflection in 'mm'

-7
-8
-8
-9
-1 0
-1 0 3 Kg.
-1 2 3 K g. -1 1 6 Kg.
6 K g. -1 2 9 Kg.
-1 4 9 K g. -1 3 12 K g.
12 Kg. -1 4 15 K g.
-1 6 15 Kg. -1 5 18 K g.
18 Kg. -1 6 21 K g.
-1 8 21 Kg. 25 K g.
-1 7

0 5 00 0 10 00 0 1 50 00 200 00 2 50 00 3 00 00 0 5000 10000 15000 20000 25000 30000
N u m b e r o f C y c le s N u m b e r o f C y c le s

GFRP + Epoxy + SW Blade GFRP + Epoxy + SW Blade

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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.

REFERENCES

1) T.Y. Kam, J. H. Jiang, H. H. Yang, R. R. Chang, F. M. Lai, and Y. C. Tseng,
“Fabrication and Testing of Composite Sandwich Blades for a Small Wind Power
System”, PEA-AIT International Conference on Energy and Sustainable
Development: Issues and Strategies (ESD 2010), June 2010.
2) Jorge Antonio Villar A1e, Gabriel da Silva Simioni, Joao Gilberto Astrada Chagas
Filho, “Procedures Laboratory for Small Wind Turbines Testing”.
3) Jorge Antonio Villar A1e, Carlos Alexander dos, Santos, “Aerodynamic Loads of
Fatigue of Small Wind Turbine Blades: Standards and Testing Procedure” EWEA
2011-Europe’s Premier Wind Energy Event 14-17-March 2011, Brussels, Belgium.

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4) Brian Hayman, Jakob Wedel-Heinen, Povl Brondsted, “Materials Challenges in
Present and Future Wind Energy” Harnessing Materials for Energy, MRS Bulletin,
Volume 33, April 2008.
5) Jayantha A Epaarachchi and Philip D Clausen “Accelerated full scale fatigue testing
of a Small Composite Wind Turbine Blade using a Mechanically operated test rig”
SIF-2004 Structural Integrity and Fracture.
6) DET Norske Veritas “Design and Manufacture of Wind Turbine Blades, Offshore
and Onshore Wind Turbines”– October 2006.
7) Jayantha A. Epaarachchi, Philip D. Clausen “An empirical model for fatigue behavior
prediction of glass fiber-reinforced plastic composites for various stress ratios and test
frequencies” Journal of Applied Science and manufacturing – 2003.
8) P.Rajaram 1 A.Murugesan 2 and G.S.Thirugnanam “Experimental Study on behavior
of Interior RC Beam Column Joints Subjected to Cyclic Loading” International
Journal Of Applied Engineering Research, Dindigul Volume 1, No 3, 2010 Research
Article Issn 09764259.
9) Nitin Tenguria 1 , Mittal.N.D 1 , Siraj Ahmed 2 “Design and Finite Element Analysis
of Horizontal Axis Wind Turbine blade” Journal of Materials Processing Technology
167 (2005) 463–471
10) M. Grujicic, G. Arakere, E. Subramanian, V. Sellappan, A. Vallejo, and M. Ozen
“Structural-Response Analysis, Fatigue-Life Prediction and Material Selection for 1
MW Horizontal-Axis Wind-Turbine Blades” – 2009.

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Finite element analysis and experimental investigations

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