Design and Performance Analysis on the Airfoil Shape of Horizontal Axis Wind Turbine

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Design And Performance Analysis on the airfoil shape of Horizontal Axis Wind Turbine

1Thae Mon Aung Thin Zar Lin, 2Myat Myat Soe, 3Win Pa Pa Myo

1M.E Student, 2Asst.Professor, 3Asst.Professor

Department of Mechanical Engineering

Mandalay Technological University, Mandalay, Myanmar

, ,

Abstract—The objective of this paper is to design and flow analysis on the airfoil shape of a horizontal axis wind turbine for 5kW power generation. For various aerodynamic forces and the required power, Blade Element Momentum Theory is used. The velocity and pressure distribution on the blade is analysed by COMSOL Multiphysics software. After observation the flow analysis on the blade of various airfoil type, NACA 4409 airfoil with angle of attack 5° is more suitable than other airfoil type to get the optimum blade design. So, this blade design can be provided to construct the HAWT where the average wind speed with 4.5m/s.

Keywords –Aerodynamics,BEM, HAWT, Wind Turbine

I.INTRODUCTION

Wind power has been identified as a clean renewable energy source that does not contribute to global warming and is known without emissions or harmful wastes.Wind power is one of the most important sources of renewable energy. Wind turbine is a device, which converts the kinetic energy from the wind to mechanical energy and then final output of electrical energy is obtained.Optimizing a blade design means maximizing the power output and so a suitable solution to blade element momentum (BEM) equations is necessary. The main flows are (1)Axial flow field (2)Tangential flow field (3)Radial flow field.A wind turbine consists of several main parts, i.e. the rotor, gearbox, generator, driven chain, control system and so on. Power is transferred from the wind to the rotor then passed through the gearbox, generator, and power electronics until it finally reaches the grid. Each stage of the power transfer has a certain efficiency.

II. Wind Turbine Technology

A. Types of Wind Turbine

This paper is restricted to Horizontal-Axis Wind Turbines within two general configurations of wind turbines, horizontal axis and vertical-axis wind turbines. In the Horizontal Axis Wind Turbine, the rotor which is located on the top of a tower with generators and gearboxes is mounted on a horizontal axis and perpendicular to the shaft. This type (HAWT) needs to have yaw drive. In this type, turbine blades are connected to a

shaft which is rotating on a horizontal axis. The rotor should be positioned in line with the wind direction by means of a tail or active yawing by a yaw motor.

Figure 1. Horizontal Axis Wind Turbine and Vertical Axis Wind

Turbine

B.Horizontal Axis Wind Turbine

Typical Horizontal-Axis Wind turbine for generating electricity either has two or three blades. Being upwind and downwind, these three bladed wind turbines are operated “upwind’, with the blades facing into the wind and the alternator placed at the top of the tower. In both cases, the axis of the blade rotation is horizontal with respect to the ground and roughly parallel to the wind stream.Three bladed -rotor is more efficient than any other rotor in the same wind velocity and rotor size.

Figure 2. Components of Horizontal Axis Wind Turbine

III. Methodology

This paper develops the design of a 5kW wind turbine power, using Blade Element Momentum (BEM) method for each blade element. The average wind speed in Kyaukse Town (2012) is 4.58 m/s and the rated wind speed for the required power is 9.16 m/s. According to the equation (1), the length of blade is 2.76m. The number of blade is three.

Pe = (½) CpηmηgρAv3(rated) (1)

Where, Pe, electrical power =5kW

Cp, power coefficient=0.52

ηm ,mechanical efficiency=0.93 ( 0.93~0.99)

ηg, generator efficiency=0.85 ( 0.85~0.98 )

ρ, Air density=1.146 kg/m3[Steam Table; T=286.2K,P=0.97806bar, z=300m]

Figure3. Power Transmission from wind to generator

Wind power, Pw = ½ ρAv3 (2)

Rotor power, Pr =PwCp (3)

Power output from gear box, Pg = Prηm (4)

Airfoil Selection

To select the airfoil shape using Profili software, Reynolds’ Number (Re) is required. The following equation (5) to (8) are related in selection airfoil shape.

Rotational speed, N =(60λv/2πR)(5)

Angular velocity,Ω =2πN/60 (6)

Chord length, c =[16πR(R/r)]/(9λ2B) (7)

Reynolds’ Number, Re=vc/υ (8)

Where, λ=6

r=R/2

B=number of blade

υ=1.4964x10-5 m2/s [Steam table,z=300m]

By substituting the value of Re and chord length (c) in Profili software , airfoil shapes and the values of lift coefficient (CL), drag coefficient (CD) and the ratio of lift and drag coefficient (CL/CD) can be obtained. By comparing the value of CL/CD and the angle of attack (α) airfoil shape is selected. To get the efficient power the values of CL/CD should be maximize. The angle of attack also should be 3 ≤ α ≥ 7 to be stable the blades according to the effect of wind.

According to the results of CL/CD, NACA 2410 is moresuitable than other two types (NACA1412 and NACA0012) to select for the required power.

(a)NACA 2410

(b) NACA 1412

Figure 5. Airfoil Selection

Figure 4. The relation of α and CL/CD for NACA 2410, 1412 and 0012

Figure 5.The relation of CL and α for NACA2410

B. Design of Blade Profile for each section

The procedure develops a preliminary design of the turbine blades by solving Equation (9)-(19) for each differential blade elements in each radial position.

Radius of each section, ri=ri-1+dr (9)

Chord length, c=(ri . SP)/(B.CL) (10)

Tip speed ratio for each section, λi= λ (ri/R) (11)

Thickness, t=0.1 c ( 10% of chord length) (12)

SP: shape parameter [Fig.12]

Wind angle, ϕ=tan-1[(2/3)(1/λi)] (13)

Blade Setting Angle, β= φ-αc(14)

Aspect Ratio, AR=R/cavg (15)

Blade Correction Angle,

αc = α0+{(CL/0.11).[1+(3/AR)]}(16)

Zero angle of attack, α0 = -1.8 at CL=0 [Figure.7]

Linear velocity, ωi=reiΩ(17)

Relative velocity, vi=(v2rated +ωi2)1/2(18)

Area of each element,

d A=1/2 (ci cosβi+ ci+1 cosβi+1 ).dr (19)

Aerodynamic Forces, Torque and Power

Figure 6. Angles, Wind Speed and Forces on Blade Element

Lift Force, dFL=1/2 ρa dAb vi2CL(20)

Drag Force, dFD=1/2 ρa dAb vi2CD(21)

Thrust Force, dFT=(dFL cosϕ + dFD sinϕ)(22)

Torque, dT=rei (dFL sinϕ - dFD cosϕ ) (23)

Power, dPr=ΩT(24)

IV.Results And Discussion

A. Theoretical Results

TABLEI

Results Datafor Each Section

Cross Section No. / ϕ(°) / β(°) / c(m) / t(m)
1 / 53 / 46 / 0.341 / 0.031
2 / 33 / 26 / 0.627 / 0.063
3 / 23 / 17 / 0.559 / 0.056
4 / 18 / 11 / 0.470 / 0.047
5 / 14 / 8 / 0.417 / 0.042
6 / 12 / 5 / 0.382 / 0.038
7 / 10 / 3 / 0.343 / 0.034
8 / 9 / 2 / 0.298 / 0.03
9 / 8 / 1 / 0.265 / 0.026
10 / 7 / 0.7 / 0.225 / 0.023
11 / 6.9 / 0.04 / 0.205 / 0.02
12 / 6.3 / -0.54 / 0.2 / 0.02

Figure7. Blade Profile

TABLE II

Aerodynamic Forces, Torque and Power for

Each Sectionof Blade

Cross Section No / dFL
(N) / dFD
(N) / dFT
(N) / dT
(Nm) / dPr
(W)
1 / 5.27 / 0.08 / 3.23 / 1.44 / 18.00
2 / 12.19 / 0.19 / 10.25 / 3.80 / 65.19
3 / 17.60 / 0.28 / 16.19 / 5.55 / 100.27
4 / 23.07 / 0.36 / 22.00 / 7.19 / 133.15
5 / 29.59 / 0.47 / 28.71 / 9.07 / 170.78
6 / 36.42 / 0.57 / 35.68 / 10.98 / 208.82
7 / 42.03 / 0.66 / 41.41 / 12.44 / 238.18
8 / 46.73 / 0.73 / 46.22 / 13.60 / 261.34
9 / 50.35 / 0.79 / 49.92 / 14.41 / 277.49
10 / 53.60 / 0.84 / 53.24 / 15.09 / 291.08
11 / 60.14 / 0.95 / 59.81 / 16.66 / 322.43

TABLE III

Power Transmission DirectlyBy Wind Speed

Wind speed(m/s) / Pw(W) / Pr(W) / Pg(W) / Pe(W)
vcut-in=3.21 / 452 / 249 / 239 / 215
4.4 / 1166 / 641 / 615 / 554
5.6 / 2404 / 1322 / 1269 / 1142
6.8 / 7008 / 3854 / 3700 / 3330
9.2 / 10659 / 5862 / 5628 / 5065
10.4 / 15398 / 8469 / 8130 / 7317
11.6 / 21367 / 11751 / 11281 / 10153
12.8 / 28707 / 15789 / 15157 / 13641
vcu-tout=13.74 / 35508 / 19529 / 18748 / 16873

Figure 8. Power and Wind Speed

B. Numerical Results

Imports the selectedNACA airfoil geometry which exported from the Profili software with the correct chord length to COMSOL Multiphysics. And create sufficient fluid domain. Then, rotate to the correct angle of attack.

Using Incompressible Navier-Strokes equation and Steady-state analysis, insert constants and properties of fluid domain and airfoil geometry. Inlet velocity is 3.21m/s (cut-in velocity).

Boundary condition of inlet is velocity and outlet is pressure, no viscous stress. Boundary conditions of rectangle are summetry and airfoil geometry is wall and no slip. Density and Reynolds’ number are used same as theoretical results.

(a)

(b)

Figure9. (a) Velocity plot and (b) Pressure plot (NACA 2410)

(a)

(b)

Figure 10. (a) Velocity plot and (b) Pressure plot (NACA 1412)

(a)

(b)

Figure 11. (a) Velocity plot and (b) Pressure plot (NACA 0012)

So, according to the result Table (II) and (III), total electrical power for wind turbine by sectional and whole unit are approximately equal. By observing the simulation results from Figure (9) to Figure (11), velocity distribution on the upper surface of the airfoil is greater than on the lower surface of it. And pressure distribution on the upper surface of the airfoil is less than on the lower surface of it. Among them, Figure (9), for NACA 2410 with angle of attack 5° is the most suitable to get the optimal blade design because the velocity and pressure distribution are more acceptable than other two types according to the average wind speed 4.5m/s. Moreover it’s maximum lift and drag coefficient ratio is greater than other two types. By theoretically, to get the optimum blade design maximum lift and drag coefficient ratio is as much as possible.

V. Conclusion

The required power can be calculated by using both BEM theory on each section of the blade and the power equations from wind to electrical. Testing in COMSOL Multiphysics, it can be found that the velocity flow is increased when the ratio of CL/CD is increased. The relation of velocity flow and power output can also be tasted by changing the angel of attack with this numerical method.

Acknowledgment

The author wishes to mention her heartfelt thanks to her Supervisor, Dr. Myat Myat Soe, Associate Professor, Department of Mechanical Engineering, Mandalay Technological University, for giving valuable suggestion, wise guidance, supervision and kind help to the completion of this paper. The author would like to express her deepest sense of gratitude and respect to her Co-supervisor, Dr. Win Pa Pa Myo, Associate Professor, and Dr Thein Min Htike, Lecturer, Department of Mechanical Engineering, Mandalay Technological University for their encouragement, helpful suggestion, true-line guidance, supervision and editing this paper.

References

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[2]Qiyue Song, Design, Fabrication, and Testing of a New Small Wind Turbine Blade, 2012

[3]Siraj Ahmed2, Evaluation of Performance of HAWT Blades Based On Optimal Rotor Theory, India, 2011

[4]Michael Schmidt, Wind Turbine Design Optimization. Strategic Energy Institute, Georgia Institute of Technology, 2011

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[10] wind power.com

[11]

Appendix

Figure 12. Shape Parameter and Speed ratio

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