11151 FACTA UNIVERSITATIS Series: Electronics and Energetics Vol. 36, No 2, June 2023, pp. 239-251 https://doi.org/10.2298/FUEE2302239S © 2023 by University of Niš, Serbia | Creative Commons License: CC BY-NC-ND Original scientific paper STRENGTH ANALYSIS OF A BLADE WITH DIFFERENT CROSS-SECTIONS* Bader Somaiday1, Ireneusz Czajka1, Muhammad A. R. Yass2 1AGH University of Science and Technology, Krakow, Poland 2University of Technology, Baghdad, Iraq Abstract. The efficiency of horizontal axis wind turbine (HAWT) blades is examined in this paper concerning the effect of cross-section airfoil type. Three dif-ferent airfoils were examined: symmetric (NACA 4412), asymmetric (NACA 0012), and supercritical (NACA 4412). (EPPLER 417). The anal-yses that were performed combined theory and experiment. Theoretical analyses were carried out using Fortran 90 code and the blade element momentum-based Qblade code. The blade was created using SolidWorks software and a 3D printer for testing purposes. The findings of experi-mental tests supported the conclusions of the theory. Research revealed that the EPPLER 417 blade, which has a supercritical airfoil, performed better than other examined objects. NACA 4412, NACA 0012, and EPPLER 417 each have a power coefficient of 0.516, 0.492, and 0.510. According to the experimental data, the EPPLER 417 airfoil outperforms other air-foils in terms of power and speed reduction. To calculate the deformation and stresses of the three blades with various cross sections, CFD analysis was done in ANSYS Workbench. The CFD results showed that NACA 4412 has the highest strength but EPPLER 417 was considered the optimum cross-section based on power generation and acceptable stress values. Key words: HAWT, CFD analysis, Optimum power coefficient, Qblade code 1. INTRODUCTION The aerodynamic efficiency of an airfoil is defined by the lift-to-drag ratio. It achieves the highest values at a specific angle of attack, and the value of this angle varies between airfoils. [2] The lift-to-drag ratio depends on zero-lift drag, aspect ratio, and span efficiency and is independent of weight. The use of airfoil in a wind turbine is no more limited than in an aircraft wing because a wind turbine operates at a lower speed than an aircraft. [3] There have been many theoretical and scientific studies on the performance of wind turbine blades. Received September 29, 2022; revised December 11, 2022; accepted January 06, 2023 Corresponding author: Bader Somaiday AGH University of Science and Technology, Krakow, Poland E-mail: somaiday@agh.edu.pl * An earlier version of this paper was presented at the 7th Virtual International Conference Science, Technology and Management in Energy (eNergetics 2021), Belgrade, Serbia, December 16-17 2021 [1]. mailto:somaiday@agh.edu.pl 240 B. SOMAIDAY, I. CZAJKA, M. A. R. YASS Symbols a Axial factor á Angular factor Cd Drag coefficient Cl Lift coefficient Cp Power Coefficient N Number of revolutions of rotor per minute (rpm) P Power (W) r Radius (m) R Radius of turbine rotor (m) U Wind speed (m/s) 𝛼 Angle of attack (degree) 𝜆 Tip speed ratio φ Relative flow angle (degree) Ω Angular velocity of the rotor(rad/s) Acronyms CFD Computational Fluid Dynamics HAWT Horizontal Axis Wind Turbine BEM Blade Element Momentum NACA National Advisory Committee for Aeronautics FEM Finite Element Method URANS Unsteady Reynolds Averaged Navier-Stokes [4] This paper investigated an aerodynamic performance evaluation system using two groups of NACA profiles which were used in a series of five-digit NACA (63-221, 65- 415; 23012,23021) and four-digit NACA (2421, 2412,4412, 4424) for three HAWT blades. The same airfoils were used along the entire blade. A computer pro-gram was developed to automate the entire procedure. Their results show that the elementary power coefficient of NACA 4412 and NACA 23012 was higher than the other profiles. [5] In this paper, a stable and aerodynamic design using NACA 4412 profile with blade length (800 mm) and power (600 W) with mini HAWT was pro-posed. The length chord and twist angle distributions of the initial blade model were calculated. A reasonable compromise between high efficiency and good starting torque was obtained. The blades were developed using MATLAB software. The op-timized blade chord was reduced by 24% and the thickness by 44%. The power level of the optimized blade was significantly increased to 30% compared to the standard blade. [6] This paper explained the design and optimization of a small HAWT blade using custom code. The blades were made using NACA 4412, NACA 2412 and NACA 1812 at a wind speed of 5 m/s, which was the most frequent wind speed pre-vailing in the Indian peninsula. Based on a self-created code based on BEM theory, an optimum blade profile was generated which performs with high efficiency using multiple airfoils. The twist angle distribution, chord distribution and other parame-ters for different airfoil sections along the blade were determined using the proposed code. For a rotor with a diameter of 4.46 m, a power factor of 0.490 and an output power of 0.56 kW was obtained. The blade analysis result obtained using Q-blade software showed reliable agreement with the proposed code and wind turbine per-formance analysis. The power factor obtained using the MATLAB code was 0.490, which was very close to that obtained using Q-blade (0.514). In addition, the differ-ence in output power between the two values was only 28.58 W. [7] The behaviour and performance of a multi-section HAWT blade with and without a fence are researched in this paper. The multi-section HAWT blade was designed using supercritical airfoils (SG6043, FX63-137S and FX66-S-196V). The overall performance of the multi-section blade was compared with the single-section NACA4412 blade. Numerical analyses were performed using the author's code (Fortran 90) and the Qblade package based on BEM theory. The multi-pass vanes show an increase of about 8% in power factor compared to the single-pass vanes. The boundary layer theory was used to design the fences and their Strength Analysis of a Blade with Different Cross-Sections 241 position was de-termined experimentally. An increase in total power factor of about 16% with the use of fences and high flutter stability. [8] This paper investigated the aero-elastic behavior of horizontal axis wind tur-bine (HAWT) flexible blades by using computational and aerodynamic models ap-proach. To study the unstable blade airfoil aerodynamic properties, the B-L (Bed-does-Leishman) dynamic stall model was added to the modified Blade Element Mo-mentum (BEM) model. [9] In this paper investigation of the aero-elastic model of multi-rotor HAWT was done. The method used in this system was to integrate the single-rotor HAWCStab2 with the multi-rotor tool HAWC2. Therefore, this method of fidelity linear time-invariant aero elastic modelling was verified by comparing the frequency responses of different rotors. [10] This paper studied the aero elastic be-havior of a MW (multi-megawatt) HAWT is influenced by the integrity of the aero-dynamic simulation. The main purpose of this research is the comparison between engineering model results and CFD aero elastic simulations results that needs less empirical modeling. To investigate the influence of the aerodynamic models on the aero elastic results for large HAWT, two distinct models (BEM- and CFD-based) were used. [11] The two-part study looks at horizontal axis wind turbines which have improved aero elastic performance and hence boost yearly energy output is proposed in this paper. The structural characteristics of a standard blade were then idealized using an adaptable shear. This development's power curve is evaluated, and it is proven to dramatically boost yearly energy output over traditional systems by 1.51 % than the maximum power at a wind speed of 15 m/s. [12] Researchers developed the URANS equations that were integrated with the FEM in a flexible way to describe the aero-elastic behaviour of Tjreborg horizontal axis wind turbine blades. At four different horizontal inflow wind speeds, this approach was validated by comparing simulated and experimental data. The aero-elastic behaviour of the Tjreborg wind turbine was also estimated and studied for yaw angles of 10, 30, and 60 degrees. [13] This research was done by developing a horizontal axis wind tur-bine rotor blade model for showing the coupling effect of rotor bulk rotation and blade flexible motion. The model was created with Lagrange's technique, as well as the blade was discretized utilizing the finite element method (FEM). The two differ-ent relationships between aerodynamics wind and structural behavior are captured in this design. [14] Researchers developed a wind speed model for n-blades of hori-zontal axis wind turbines with the considerations of wind shear and buildings shad-ow impacts. The systematic approach was utilized to calculate the wind shear, build-ing shadows, synthesis, and equivalent wind velocity disturbances elements, as well as their relative positions in the rotor disc region. [15] This paper investigated the influence of diagonally input upon the wake parameters of a HAWT (Horizontal Axis Wind Turbine) inside a wind farm. A HAWT with a generator limit of 30 kW and then rotor diameter of 10.0 m was employed in this work. A field study was used to analyse the influence of tilt angle on the energy and thrust efficiency of a HAWT. On this foundation, the HAWT's wake properties were investigated with various wind orientations and pitch angles. As a result, the peak power coefficients Cp were 0.31, 0.33, and 0.27, respectively, and correlate to tip velocity ratios l= 7.5, 7.4, and 6.8 with pitch angles b= 0°, 2°, and 4°. The wind turbine experimental model predicts around 51% of annual power generation compared to the experimental research model. In this study, the behavior and performance of different blade cross-sections, symmetrical, asymmetrical and supercritical airfoils (NACA0012, NACA 4412 and EPPLER 417) were investigated experimentally and by ANSYS. The horizontal axis wind turbine blade design was performed using Fortran 90 code and QBlade software based on BEM theory. 242 B. SOMAIDAY, I. CZAJKA, M. A. R. YASS 2. THE BLADE CROSS-SECTION Table 1 shows the airfoil characteristics in cross sections and the airfoil shapes are shown in Figure 1. The HAWT rotor design parameters are shown in Table 2. Table 1 Cross-Section Airfoils Distribution Airfoil Max t/c Max Cl/Cd NACA 4412 12% at 30% 129.4 at 5.25° NACA 0012 12% at 30% 75.6 at 7.5° EPPLER 417 14.2% at 38.35% 135.9 at 2.25° Fig. 1 Airfoils geometry Table 2 Parameter of Design Rotor Diameter 1.07 m Hub Diameter 0.20 m Number of Blades 3 Rated Power 600 W Cut in Speed 2 m/s2 3. POWER COEFFICIENT Fig. 2 shows maximum power that can be produced by wind flowing through the ring. [7]. The velocity around the disc is assumed to be constant (U2 = U3) with the assumption that the upstream and downstream pressures are equal. The equations yield the rotor power coefficient. Equations [16]. 1 4 2 2 U U U + = (1) Strength Analysis of a Blade with Different Cross-Sections 243 1 2 1 U U a U − = (2) 2 1 (1 )U U a= − (3) 4 1 (1 2 )U U a= − (4) h h R R r r P dP dQ= =   (5) 2 3 1 1 2 h R r p wind dQP C P R U  = =  (6) \ 3 2 8 (1 ) 1 cot h d p r r l C C a a d C         =  − −           (7) The tip speed ratio; 1 2 60 R N U   = (8) Fig. 2 Wind turbine actuator disk model 4. DESIGN AND MANUFACTURING BLADES A program in FORTRAN (f.90) was written and the Qblade package was used to calculate the aerodynamic data and power factor based on Blade Element Momen-tum (BEM) theory, as shown in Tables 3, 4 and 5 and Figure 3. Solidworks software was used to design the 3D blade shapes (see Figure 4). The developed models were fabricated on a 3D printer (see Figure 5). Due to the limited size of the printer's print area, the blades were divided into several sections and then combined. The blades with different profiles in sections (NACA 4412, NACA 0012 and EPPLER 417) were mounted to the wind turbine for testing as shown in Figure 6. 244 B. SOMAIDAY, I. CZAJKA, M. A. R. YASS Table 3 NACA 4412 Cross-Section Geometry Position (m) Chord (m) Twist (deg) Foil 1 0.00 0.167 43.42 NACA 4412 2 0.10 0.156 23.14 NACA 4412 3 0.17 0.136 16.72 NACA 4412 4 0.27 0.109 10.91 NACA 4412 5 0.37 0.090 7.42 NACA 4412 6 0.47 0.076 5.11 NACA 4412 7 0.57 0.066 3.47 NACA 4412 8 0.67 0.058 2.25 NACA 4412 9 0.77 0.052 1.30 NACA 4412 10 0.87 0.046 0.56 NACA 4412 11 0.97 0.042 -0.05 NACA 4412 12 1.07 0.038 -0.56 NACA 4412 Table 4 NACA 0012 Cross-Section Geometry Position (m) Chord (m) Twist (deg) Foil 1 0.00 0.206 41.43 NACA 0012 2 0.10 0.194 21.14 NACA 0012 3 0.17 0.168 14.72 NACA 0012 4 0.27 0.136 8.91 NACA 0012 5 0.37 0.112 5.42 NACA 0012 6 0.47 0.094 3.11 NACA 0012 7 0.57 0.082 1.47 NACA 0012 8 0.67 0.072 0.25 NACA 0012 9 0.77 0.064 -0.69 NACA 0012 10 0.87 0.057 -1.44 NACA 0012 11 0.97 0.052 -2.05 NACA 0012 12 1.07 0.048 -2.56 NACA 0012 Table 5 EPPLER 417 Cross-Section Geometry Position (m) Chord (m) Twist (deg) Foil 1 0.00 0.283 47.42 EPPLER 417 2 0.10 0.266 27.14 EPPLER 417 3 0.17 0.231 20.72 EPPLER 417 4 0.27 0.186 14.90 EPPLER 417 5 0.37 0.153 11.42 EPPLER 417 6 0.47 0.129 9.11 EPPLER 417 7 0.57 0.112 7.47 EPPLER 417 8 0.67 0.098 6.25 EPPLER 417 9 0.77 0.087 5.31 EPPLER 417 10 0.87 0.079 4.55 EPPLER 417 11 0.97 0.072 3.94 EPPLER 417 12 1.07 0.066 3.44 EPPLER 417 Strength Analysis of a Blade with Different Cross-Sections 245 Fig. 3 Cross-section blades by Qblade package Fig. 4 Cross-section blade by SolidWorks (a) NACA 4412 Blade (b) NACA 0012 Blade (c) EPPLER 317 Blade Fig. 5 3D Printing Process 246 B. SOMAIDAY, I. CZAJKA, M. A. R. YASS Fig. 6 Wind turbines (a) with NACA4412 cross-section blades (b) with NACA0012 cross-section blades (c) with EPPLER 317 cross-section blades The material assigned to the blades was carbon fiber and its properties are shown in Figure 7. Applied pressure was 14.25 MPa, 251 MPa, 986.4 MPa and 1370 MPa to derive the post-processing results of Total Deformation, Equivalent Stress and Equivalent Strain shown in Table 7. Fig. 7 Carbon Fiber Properties Strength Analysis of a Blade with Different Cross-Sections 247 5. RESULTS AND DECISIONS The primary design element of a wind turbine blade is the cross-sectional area of the airfoil, which transforms the airflow velocity into a pressure distribution throughout the length of the blade. In this investigation, many profiles including symmetrical, asymmetrical, and supercritical have been used. When evaluating the performance of the profiles, the primary factors to consider are the amount of energy absorbed from the free stream, the maximum lift-to-drag ratio, and the angle of attack. Not just the power factor peak, but also the airfoil's overall cross-sectional efficiency, was taken into account. Figure 8 demonstrates that compared to the other profiles, the EPPLER 417 profile produced less drag. Additionally, as shown in Figure 9, the Eppler 417 profile produced the greatest pressure dispersion in the second third of the blade radius. As indicated in Fig. 10, the NACA 4412 profile had the highest power factor value (Cp = 0.516), followed by the NACA 0012 (Cp = 1.491), and the Eppler 417 (Cp = 0.510) profiles. However, according to Figure 11, the Eppler 417 profile had the highest overall efficiency. According to the experimental findings (see Table 6), Eppler 417 performs the best and produces the most power of the other profiles. CFD results showed that NACA 4412 goes through less deformation and stresses (Figures 12 to 17 and Table 7). Fig. 8 Normal force distribution along the blades radius Fig. 9 Tangential force distribution along the blades radius 248 B. SOMAIDAY, I. CZAJKA, M. A. R. YASS Fig. 10 The power coefficient of the cross-sections blades versus tip speed ratio Fig. 11 The area under power coefficient curve (a) NACA 4412 cross-section blade (b) NACA 0012 cross-section blade (c) EPPLER 317 cross-section blade Strength Analysis of a Blade with Different Cross-Sections 249 Table 6 Experimental Results Wind speed (m/s) NACA 4412 NACA 0012 EPPLER 417 rpm Power W rpm Power W rpm Power W 3 62 13 51 10 68 20 4.2 88 93 69 28 95 122 5.4 107 144 96 125 122 173 6.5 125 306 114 285 147 330 7.5 171 506 132 363 178 546 Fig. 12 Equivalent Stress for NACA 4412 at 251 Pa and 1370 Pa Fig. 13 Equivalent Stress for NACA 0012 at 251 Pa and 1370 Pa Fig. 14 Equivalent Stress for EPPLER 417 at 251 Pa and 1370 Pa Fig. 15 Total Deformation for NACA 4412 at 251 Pa and 1370 Pa 250 B. SOMAIDAY, I. CZAJKA, M. A. R. YASS Fig. 16 Total Deformation for NACA 0012 at 251 Pa and 1370 Pa Fig. 17 Total Deformation for EPPLER 417 at 251 Pa and 1370 Pa Table 7 CFD Results Blade Models Applied Pressure (Pa) Total Deformation (mm) Equivalent Stresses (MPa) Equivalent Strain (mm/mm) EPPLER 417 14.25 0.1016 0.0653 3.49E-06 251 1.7888 1.1505 6.15E-05 986.4 7.0299 4.5213 2.42E-04 1370 9.7638 6.2796 3.35E-04 NACA 0012 14.25 0.4138 0.1628 8.70E-06 251 7.2898 2.8688 1.53E-04 986.4 28.648 11.274 6.02E-04 1370 39.789 15.659 8.37E-04 NACA 4414 14.25 2.05E-04 1.49E-04 8.13E-09 251 3.61E-03 2.62E-03 1.43E-07 986.4 1.42E-02 0.01028 5.63E-07 1370 1.97E-02 0.01427 7.81E-07 6. CONCLUSIONS The effects of several cross-section airfoil types on the effectiveness of HAWT blade efficiency were studied. Analysis was done on three different airfoils: supercritical (EPPLER 417), asymmetric (NACA 0012), and symmetric (NACA 4412). The analyses that were performed combined theory and experiment. 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