6340(Print), ISSN (Online) AND TECHNOLOGY Volume 3, Issue 3, Sep- (IJMET) Dec (2012) IAEME

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1 INTERNATIONAL International Journal of Mechanical JOURNAL Engineering OF MECHANICAL and Technology (IJMET), ENGINEERING ISSN (Print), ISSN (Online) AND TECHNOLOGY Volume 3, Issue 3, Sep- (IJMET) Dec (212) IAEME ISSN (Print) ISSN (Online) Volume 3, Issue 3, September - December (212), pp IAEME: Journal Impact Factor (212): (Calculated by GISI) IJMET I A E M E FINITE ELEMENT ANALYSIS AND EXPERIMENTAL INVESTIGATIONS ON SMALL SIZE WIND TURBINE BLADES ABSTRACT T.Vishnuvardhan, Associate Professor, Intell Engineering College, Anantapur.A.P Dr.B.Durga Prasad, Associate Professor, JNT University, Anantapur.A.P 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 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 493

2 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 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 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 Upper Surface Values Lower Surface Values Station Ordinate Station Ordinate

3 L.E. Radius = percent c Slope of Mean Line at LE =.1685 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 1 Airfoil Ordinates A i r f o i l S t a t i o n s Fig: 1 NACA 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 1. 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. 495

4 Fig: 2 R21 SWT Blade Assembly Fig: 3 R22 SWT Blade Assembly Fig:4 Static Analysis of R-22- GFRP + Epoxy + SW Blade - at.245 N/mm 2 Wind Pressure - Displacement Fig:5 Static Analysis of R-22- GFRP + Epoxy + SW Blade - at.245 N/mm 2 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 496

5 Fig:1 Modal Analysis of R-22- GFRP + Epoxy + SW Blade V Mode Fig: 11 Harmonic Analysis of R-22- GFRP + Epoxy + SW Blade Root at.245 N/mm 2 Wind Pressure - Displacement Fig: 12 Harmonic Analysis of R-22- GFRP + Epoxy + SW Blade Mid at.245 N/mm 2 Wind Pressure - Displacement Fig: 13 Harmonic Analysis of R-22- GFRP + Epoxy + SW Blade Tip at.245 N/mm 2 Wind Pressure - Displacement Fig: 14 Harmonic Analysis of R-22- GFRP + Epoxy + SW Blade Root at.245 N/mm 2 Wind Pressure - Vonmises Stress Fig: 15 Harmonic Analysis of R-22- GFRP + Epoxy + SW Blade Mid at.245 N/mm 2 Wind Pressure - Vonmises Stress Fig: 16 Harmonic Analysis of R-22- GFRP + Epoxy + SW Blade Tip at.245 N/mm 2 Wind Pressure - Vonmises Stress Fig: 17 Partial Deflection of the Blade 497

6 Fig: 18 Cyclic Load of 15 Kg. Applied on the Blade Fig:19 Cyclic Load of 25 Kg. Applied on the Blade 6 Load D eflection Test Load Applied at TIP Blade Profile - R 22 5 Material - GFRP+EPOXY+ SW Tip Mid Root Fig: 2 Failure at the Root of Blade in Cyclic Load Test Load in 'Kgs' Fig:21 Load Deflection Test - R-22 - GFRP + Epoxy + SW Blade Load Applied at Tip Load Deflection Test Load Applied at MID Blade Profile - R22 Material - GFRP+EPOXY+ SW 5 Load Deflection Test Load Applied at ROOT Blade Profile - R22 4 Material - GFRP+Polyester + SW Tip Mid Root Tip Mid Root Load in 'Kgs' Fig:22 Load Deflection Test - R-22 - GFRP + Epoxy + SW Blade Load Applied at Mid Load in 'Kgs' 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. 498

7 Table 2 R21 GFRP + Polyester Solid Blade - MODE Frequency Values 1 I II III IV V Table 3 R21 - GFRP + Polyester + SW - MODE Frequency Values 1 I II III IV V Table 4 R21 GFRP + Epoxy + SW - MODE Frequency Values 1 I II III IV V Table 5 R22 GFRP + Polyester Solid Blade - MODE Frequency Values 1 I II III IV V Table 6 R22 GFRP + Polyester + SW - MODE Frequency Values 1 I II III IV V Table 7 R22 GFRP + Epoxy + SW - MODE Frequency Values 1 I II III IV V 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. 499

8 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 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 15 mm 61 mm 95 mm 2 R22 2 mm 66 mm 13 mm The load deflection test results for R22 profile blade produced from GFRP + Epoxy + SW material are represented in Figures 21, 22 and 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 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 5

9 blades with constant number of cycles (3) 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 C yclic Load - D eflection T esti - R 21- G F R P + P olyster S olid B lade 1 C y c lic L o a d - D e fle c tio n T e s ti - R G F R P + P o ly s te r S o lid B la d e K g. 6 K g. 9 K g. 12 K g. 15 K g K g. 6 K g. 9 K g. 1 2 K g. 1 5 K g. Number of Cycles Num ber of Cycles Fig.24 Cyclic Load Test Results of R-21 GFRP + Polyester Solid Blade Fig.25 Cyclic Load Test Results of R-22 GFRP + Polyester Solid Blade 1. C y c lic L o a d - D e fle c tio n T e s ti - R G F R P + P o ly s te r + S W B la d e C y c lic L o a d - D e fle c tio n T e s ti - R G F R P + P o ly s te r + S W B la d e K g. 6 K g. 9 K g. 1 2 K g. 1 5 K g K g. 6 K g. 9 K g. 1 2 K g. 1 5 K g. 1 8 K g N u m b e r o f C yc le s Fig.26 Cyclic Load Test Results of R-21 GFRP + Polyester + SW Blade N u m b e r o f C y c le s Fig.27 Cyclic Load Test Results of R-22 GFRP + Polyester + SW Blade C yc lic L oa d - D e flec tio n T es ti - R G F R P + E p o x y + S W B la d e 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 C y c lic L o a d - D e fle c tio n T e s ti - R G F R P + E p o x y + S W B la d e 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 Number of Cycles Num ber of Cycles Fig.28 Cyclic Load Test Results of R-21 GFRP + Epoxy + SW Blade Fig.29 Cyclic Load Test Results of R-22 GFRP + Epoxy + SW Blade 51

10 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 3 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 mm below the reference point, at 3 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 21), June 21. 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 211-Europe s Premier Wind Energy Event March 211, Brussels, Belgium. 52

11 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 28. 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-24 Structural Integrity and Fracture. 6) DET Norske Veritas Design and Manufacture of Wind Turbine Blades, Offshore and Onshore Wind Turbines October 26. 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 23. 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, 21 Research Article Issn ) 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 (25) ) 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