View of AIRFOIL SELECTION FOR LARGE HAWT 14M BLADE

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Vol. 03, Issue 04,April 2018 Available Online: www.ajeee.co.in/index.php/AJEEE

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1 Rabindranath Tagore University, *Corresponding author: [email protected]

AIRFOIL SELECTION FOR LARGE HAWT 14M BLADE Praveen Kumar Nigam¹, M. K. Pradhan², Nitin Tenguriya³

Abstract:- Wind turbine provides an alternate means of generating electricity from the power of wind. Efficient extraction of the energy from wind turbine blade is depends on the wise selection of airfoil. Wind turbine blades sustain high operational loads and undergo variable environmental conditions. A proper airfoil selection is important for better aerodynamic performance, structural strength and manufacturability. In this research work five thick NACA airfoil has been chosen for design of 14m blade of model RRB V27-225 kW HAWT (horizontal axis wind turbine). Out of these five NACA airfoil 63(4)-221was chosen for design of selected wind turbine.

Keywords:- Airfoil selection, HAWT, Blade, Wind turbine.

1. INTRODUCTION

Wind energy is a major clean energy source. An airfoil selection is the basis of wind turbine blade design. Airfoil optimization is responsible for aerodynamic performance, structural strength and noise control of blade. Wind speed is generally characterized by Reynolds numbers. Improper design of blade airfoil leads to deterioration in aerodynamic performance which greatly affects the operating performance of the wind turbine.

2. LITERATURE SURVEY

W.J. Zhu et al. (2014) identified an integrated method to design new airfoil for specified rotor size and given Tip Speed Ratio of large wind turbine blades.

The airfoil was designed having objective to maximize power coefficient (Cp) in minimum chord length maintaining structural performance. The initial parameters are calculated by defining the optimum flow angle and rotor solidity.

A unique shape perturbation function was developed to make easy of design and optimize of the existing airfoils. The aerodynamic tool XFOIL was used for optimization of airfoil at Reynolds number

= 16x10⁶ and Mach number = 0.25. As a result it was shown that the optimized airfoil has a better power coefficient at a large range of angles of attack. Finally, computational fluid dynamics (CFD) and blade element momentum (BEM) technique was used for a complete blade analysis which justifies the integrated

design method [1].

R. K. Gupta et al. (2017) worked for designing a rotor blade for Reynolds number = 100,000. Design procedure included the choice of appropriate airfoil for small scale HAWT, twist and chord along the blade length. Modelling was performed on Creo-Parametric 5.0. Blade element momentum theory (BEMT) was used for aerodynamic analysis to get optimimum power and torque. Four Airfoils was selected based on their maximum L/D ratio.

The selected airfoils were SG6050, SG6043, E555, and E216, where SG6050 and E555 are thick and airfoils SG6043 and E216 are thin. Two rotors were developed through mixing of 2 airfoils in each blade. First rotor was made by mixing SG6050 & SG6043 and second rotor by mixing E555 & E216.

Thick airfoils were used at the root of the blade to provide maximum strength and thin at the tip of blade to improve aerodynamic performance.

Design was performed theoretically with the help of BEM Theory.

After theoretical calculations, torque developed by first rotor is 7.52003 at Cp=0.445 whereas second rotor 6.3792 at Cp=0.3771. These calculations were made at TSR=7, wind velocity=6 m/s and rotor diameter=2.6m. The results show that first rotor is more suitable for small scale horizontal axis wind turbine aerodynamically [2].

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2 V. Salgado (2016) developed a new method for selection of airfoil to optimize small wind turbine under low cut-in speed. Initially, airfoil data is verified using software XFOIL to check its compatibility with the simulator. To eliminate the airfoil which has low performance the arithmetic mean criteria is recursively used. Then airfoil data is transferred to Matlab for a further analysis. In later part, data points were interpolated using splines to determine glide ratio (L/D) and stability at different angles of attack. Finally three airfoils out of initial group of 189, were selected based on its performance [3]

V. Manikandan et al. (2013) chosen airfoil profile NACA 63-215 for analysis of wind turbine blade. In this analysis, software Pro/E and Hyper mesh has been used to design blades. The modelling of blade was done and created several sections from root to tip with the alteration of the original design to enhance the efficiency. For the further improvement in the efficiency and noise reduction of the blade, the winglet was included at the tip of the blade. The existing original turbine blade and modified blade with the winglet were compared for their performance [4].

C. C. Z. Zuo et al. (2017) investigated the aerodynamic performance of a modified airfoil with a single leading edge protuberance and made comparison with the airfoil NACA 63(4)-021. Spalart Allmaras turbulence model was used for the purpose of numerical simulation. As compared to the quick decrement of baseline lift coefficient, the stall angle in the modified airfoil declined and the small decline in the lift coefficient was observed. An improved post-stall performance of the modified airfoil was noticed, while the pre-stall performance was reduced.

Asymmetric flows along the span wise direction was noticed in the altered airfoil, and the local region around one shoulder of the protuberance affected from leading edge separation at pre-stall angles of attack, which can be reason for the performance decline. Experimental

visualization method, including surface tuft and smoke flow, were applied, and the asymmetric flow pattern past the protuberance was successfully captured [5].

D. Holst et al. (2017) analyzed the performance of the symmetrical airfoil NACA 0021 at 3 different Reynolds numbers = 100k, 140k, and 180k based on 180° incidence. The critical problem of blockage in a wind tunnel was ignored using an open test section. The experiment was done in respect to surface pressure distribution over the airfoil for a tripped and a baseline configuration. The pressure was used to gain lift, pressure drag, moment data. Further analysis with positive and negative pitching revealed a second hysteresis loop in the deep post stall region results in a variation of 0.2 in moment coefficient and 0.5 in lift [6].

In this research work, eight thick NACA airfoil has been chosen for design of 14m blade of model RRB V27-225 kW HAWT (horizontal axis wind turbine).

These are NACA 0018, NACA 0021, NACA 0024, NACA 16-021, NACA 63(4)-221, NACA 64(4)-221, NACA 65(4)-221and NACA 66(4)-221. Airfoil shape comparison has been done using online airfoil analysis tool. Location of Maximum thickness and maximum camber has been analysed for all airfoils in terms of percentage of chord. Then for all airfoil Cl/Cd ratio has been found at different Reynolds number.

3. METHODOLOGY 3.1 Airfoil

3.1.1 Airfoil selection

There are many airfoils specified by NACA (National Advisory Committee for Aeronautics) can be classified broadly into thin and thick airfoil. Thick airfoils are most suitable for large blades due to its structural strength. The performance criteria of best airfoil is that it must possesses maximum lift coefficient/ drag coefficient ratio. There are some of the NACA series thick airfoils shown in Table 3.1 having high L/D ratio.

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Table 3.1 4/5/6 digit thick airfoil for comparison Airfoil name Airfoil type

NACA 0018 4 digit Thick airfoil NACA 0021 4 digit Thick airfoil NACA 0024 4 digit Thick airfoil NACA 16-021 5 digit Thick airfoil NACA 63 (4)-221 6 digit Thick airfoil NACA 64 (4)-221 6 digit Thick airfoil NACA 65 (4)-221 6 digit Thick airfoil NACA 66 (4)-221 6 digit Thick airfoil 3.1.2 Airfoil shape comparison

It is important to compare airfoil shapes to achieve better aerodynamic performance. Airfoil shape defines its lift and drag coefficient (Cl, Cd) with respect to angle of attack, . Airfoil shape indicates chord length, mean line, maximum thickness, location of maximum thickness in terms of percentage of chord, location of maximum camber in terms of percentage of chord. Various airfoil shapes from NACA family having better performance are shown from Fig. 3.1 to 3.8.

Shape comparison of these airfoils is shown in Fig. 3.9 and comparative specification is listed in Table 3.2 using airfoil data tool. Comparison shows maximum thickness and maximum camber position in terms of percentage of chord. In case of 4 digit NACA series airfoil the 1^st digit shows the maximum value of the mean line ordinate in percentage of the chord. The 2^nd digit indicates the distance from the leading edge to the position of the maximum camber in tenths of the chord. The last

two digits show the thickness of airfoil in percentage of the chord.

In case of five-digit NACA series airfoil the 1^st digit indicates the value of camber in terms of the relative magnitude of the coefficient of lift. The 2^nd and 3^rd digits together show the distance from the leading edge to the position of the maximum value of camber. This distance is in percentage of the chord. The last two digits show the section thickness in percentage of the chord. In NACA 6-series airfoil, 6 is the series designation.

The 2^nd digit denotes the position of minimum pressure in tenths of the chord behind the leading edge for the basic symmetrical section at zero lift. The 3^rd digit which can be in small bracket or in subscript gives the range of lift coefficient in tenths above and below the design coefficient of lift in which favourable pressure gradients exist on both surfaces. The 4^th digit following the dash gives the design lift coefficient in tenths. The last two digits indicate the thickness of the airfoil in percentage of the chord.

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Fig. 3.9: Shape comparison of NACA airfoil 0018, 0021, 0024, 63-021, 63(4)-221, 64(4)-221, 65(4)-221, 66(4)-221

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Table 3.2 Specification comparison of airfoil NACA 0018, NACA 0021, NACA 0024, NACA 63-021, NACA 63(4)-221, NACA 64(4)-21, NACA 65(4)-221, NACA 66(4)-221

3.1.3 Airfoil sliding ratio (Cl/Cd) comparison

As maximum Cl/Cd ratio is required for achieving maximum aerodynamic performance. Using airfoil data tool maximum Cl/Cd ratio has been found at

different Reynolds number of various selected airfoil listed in Table 3.1 and shown in Table 3.3. Airfoil NACA 64(4)- 221 shows maximum Cl/Cd ratio = 107.4 at α=7.25° for Reynolds number = 10,00,000, hence, chosen for blade design.

Table 3.3 Maximum Cl/Cd ratio at different Reynolds number Airfoil Reynolds

number Max Cl /Cd

NACA 0018 5,00,000 65.8 at α=9.25°

NACA 0018 10,00,000 77.9 at α=10°

NACA 0021 5,00,000 60.6 at α=10.25°

NACA 0021 10,00,000 74.7 at α=8.5°

NACA 0024 5,00,000 52.1 at α=10.25°

NACA 0024 10,00,000 68.8 at α=9°

NACA 16-021 5,00,000 39.5 at α=5.25°

NACA 16-021 10,00,000 42 at α=4.75°

NACA 66(4)-221 5,00,000 68.6 at α=6.5°

NACA 66(4)-221 10,00,000 100.8 at α=5.5°

NACA 65(4)-221 5,00,000 86.2 at α=7.25°

NACA 65(4)-221 10,00,000 105.8 at α=6.25°

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NACA 64(4)-221 5,00,000 87.7 at α=8.25°

NACA 64(4)-221 10,00,000 107.4 at α=7.25°

NACA 63(4)-221 5,00,000 88 at α=8.5°

NACA 63(4)-221 10,00,000 108 at α=7.5°

3.1.4 Specification of selected airfoil After comparing various 4 digits, 5 digits and 6 digits thick NACA airfoils on basis of various parameters describe in Table 3.3, airfoil NACA 63(4)-221 shows high lift/drag ratio which is prime requirement of better aerodynamic performance. The specification of selected airfoil is as

follows in Table 3.4. To re-create the shape of the airfoil the set of coordinates are required. The airfoil coordinates are given in two columns, x and y separately for the upper and lower surface. Re- creation of the shape of the airfoil using the set of coordinates is shown in Fig.

3.10.

Table 3.4 Airfoil specification of NACA 63(4)-221 Upper surface Lower surface Station Ordinate Station Ordinate

0.00000 0.0000 0.00000 0.00000

0.00367 0.01627 0.00633 -0.01527

0.00600 0.02001 0.00900 -0.01861

0.01075 0.02628 0.01425 -0.02414

0.02292 0.03757 0.02708 -0.03385

0.04763 0.05375 0.05237 -0.04743

0.07253 0.06601 0.07747 -0.05753

0.09753 0.07593 0.10247 -0.06559

0.14767 0.09111 0.15233 -0.07765

0.19792 0.10204 0.20208 -0.08612

0.24824 0.10946 0.25176 -0.09156

0.29860 0.11383 0.30140 -0.09439

0.34897 0.11529 0.35103 -0.09469

0.39934 0.11369 0.40066 -0.09227

0.44969 0.10949 0.45031 -0.08759

0.50000 0.10309 0.50000 -0.08103

0.55027 0.09485 0.54973 -0.07295

0.60048 0.08512 0.59952 -0.06370

0.65063 0.07426 0.64937 -0.05366

0.70071 0.06262 0.69929 -0.04318

0.75073 0.05054 0.74927 -0.03264

0.80067 0.03849 0.79933 -0.02257

0.85056 0.02693 0.84944 -0.01347

0.90039 0.01629 0.89961 -0.00595

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Fig. 3.10 Airfoil shape of NACA 63(4)-221 4. CONCLUSION

Result shows maximum Cl/Cd for airfoil NACA 66(4)-221 and found suitable for further analysis of performance of RRB V27-225 kW HAWT (horizontal axis wind turbine) with new blade design.

5. ACKNOWLEDGEMENTS

The authors would like to acknowledge the research support from the Rabindranath Tagore University, Bhopal, India.

REFERENCES

1. W.J. Zhu, W.Z. Shen, and J.N. Sørensen,

“Integrated airfoil and blade design method for large wind turbines”, Renewable Energy, Science Direct, Vol 70, pp 172-183, 2014.

2. R. K. Gupta, V. Warudkar , R. Purohit and S. S. Rajpurohit (2017). "Modeling and Aerodynamic Analysis of Small Scale, Mixed Airfoil Horizontal Axis Wind Turbine Blade". 6th International Conference of Materials Processing and Characterization, ScienceDirect, Materials Today: Proceedings 4 (2017) 5370–5384.

3. V. Salgado, C. Troya, G. Moreno, J. Molina (2016). "Airfoil Selection Methodology for Small Wind Turbines". International journal of renewable energy research. Vol.

6, No. 4.

4. N. Manikandan, B.Stalin (2013). "Design of Naca 63215 Airfoil for a Wind Turbine". IOSR Journal of Mechanical and

Civil Engineering (IOSR-JMCE). Volume 10, Issue 2 (Nov. - Dec. 2013), PP 18-26.

5. C. C. Z. Zuo, S. Liu, T. Maeda (2017).

"Effect of a single leading-edge protuberance on NACA 634-021 airfoil Performance". Journal of Fluid Engineering.

6. D. Holst, B. Church, G. Pechlivanoglou, E.

T¨ uz ¨ uner, J. Saverin, C. N. Nayeri, C. O.

Paschereit (2017). "Experimental Analysis of a NACA 0021 Airfoil Section Through 180-Degree Angle of Attack at Low Reynolds Numbers for Use in Wind Turbine Analysis". Proceedings of ASME Turbo Expo 2017: Turbo machinery Technical Conference and Exposition.

Authors Biography

1. Praveen Kumar Nigam is Ph.D.

research scholar in the Department of Mechanical Engineering, Rabindranath Tagore University, Raisen, India. He has obtained Bachelor of Engineering From SATI, Vidisha, India, in 2003 and M.Tech. From BUIT, Bhopal, India in 2012. His current area of research includes Material science, Wind turbines, Renewal Energy.

2. M. K. Pradhan is Assistant Professor in the Department of Mechanical Engineering, and Head of Production Engineering Lab. &

Computer aided Manufacturing

0.95018 0.00708 0.94982

1.00000 0.00000 1.00000

LE Radius: 0.0265, slope of radius through LE 0.0842 -0.00076

0.00000

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8 lab of the Maulana Azad National Institute of Technology, Bhopal, India. He received his M. Tech and Ph.D. in Mechanical Engineering from NIT, Rourkela, India.

3. Nitin Tenguria received M. Tech.

and Ph.D. from NIT, Bhopal, India in 2007 and 2012. He is a Head in the Department of Mechanical Engineering, SIRT, Bhopal, India.

He has more than 10 years of experience in teaching and research. His research area includes Wind Turbine blade.