DESIGN OF VERTICAL AXIS WIND TURBINE FOR LOW WIND SPEED APPLICATION IN HIGHWAY LIJIN E M 1 & ASHOK S 2

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1 TJPRC: International Journal of Power Systems & Microelectronics (TJPRC: IJPSM) Vol. 2, Issue 1, Jun 2017, TJPRC Pvt. Ltd. DESIGN OF VERTICAL AXIS WIND TURBINE FOR LOW WIND SPEED APPLICATION IN HIGHWAY ABSTRACT LIJIN E M 1 & ASHOK S 2 Department of Electrical Engineering, National Institute of Technology Calicut, India Wind energy is considered as the fastest growing source of renewable energy. Availability of wind force will depend on the season. Highway roads can provide considerable amount of wind force to drive a turbine due to pressure difference created by the vehicle movement on both side of the median. Here design of airfoil based on vertical axis wind turbine (VAWT) for low wind speed application ranging from 2 to 8m/s is done. The main advantage of vertical axis wind turbine over horizontal axis wind turbine is that blades can have constant shape over the length. It can extract power from any direction of wind without the yaw mechanism. Due to the vehicle movement in highway wind force is created on both side of the highway in opposite direction. The VAWT can be placed on the median so that air flow on both side of highway can be extracted. The national Advisory Committee for Aeronautics NACA series blades NACA0012, NACA0015, NACA0021 Were analyzed here. The graphical relationship between optimal angle of attack and Reynolds number which predict the flow pattern were analyzed, based on this The angle of attack that generate high lift over draw ratio (C d /C l ) can be identified. KEYWORDS: Renewable Energy, Wind Power, Vertical Axis Wind Turbine, Blade Aerodynamics, PMSG Received: Feb 01, 2017; Accepted: Feb 16, 2017; Published: Feb 22, 2017; Paper Id.: TJPRC: IJPSMJUN20172 INTRODUCTION Original Article Nowadays the electric energy requirement is much higher than that its production. One of the biggest issue is that natural resources are going to be finished one day and a replacement has to be found out. Presently we are more dependent on fossil fuels, which is the main cause of global warming, pollution and greenhouse gases. In order to rectify such problems, we should give more focus on renewable energies such as sunlight, wind, rain. Energy is the fuel for development. Due to massive urbanization global demand for energy is rising rapidly. As we realize that fossil fuels are going to run out, we re trying harder to develop other means of generating the electricity on which we depend. Renewable resources, such as solar, hydro-electric, tidal powers are particularly attractive, although they are having some drawbacks. Wind energy is considered the fastest growing source of clean energy. Availability of wind force depends upon the seasonal weather condition. Sometime the wind speed will be very high, but it is highly fluctuating in nature. Highways can provide a required considerable amount of wind to drive a turbine due to pressure difference created by vehicle traffic on both side of highway. This project aims to extract this energy in the most efficient manner. Small vertical axis wind turbines can be installed in the medians of highway to extract this wind power. The wind turbines will be placed on the road dividers so that wind flow from both sides of the highway will be acting tangentially in opposite directions on both sides of the vertical axis wind turbine. These types of turbines can be installed on express highways and other high speed traffic areas to generate electricity. The generated power

2 12 Lijin E M & Ashok S from these kind of turbine can be used for providing power to street lights, traffic lights etc. This kind of VAWT proposes an independent power supply for highways. Also this system can be connected to the grid to cater the demand in the main grid[1]. Wind turbines can be classified according to orientation of rotor axis and the type of aerodynamic forces used to take energy from wind. Depending upon the. The major classification of wind turbines is related to the rotating axis position in respect to the wind direction. Horizontal Axis Wind Turbines (HAWT): In HAWT the axis of rotation of the turbine will be oriented parallel to the wind in order to produce power. Majority of the wind turbine are of HAWT [2]. Vertical Axis Wind Turbines (VAWT): In VAWT the axis of rotation is perpendicular to the wind direction. The main advantage of VAWT is that the blades can be have same dimension along the length and there is no need of yaw mechanism to orient the blade in the direction wind. As the WAVT are very close to ground wind speeds available are lower. Another advantage of VAWT is that the generator can be mounted easily in ground itself [3]. SIGNIFICANCE OF THE PROJECT We are mainly depending on non-renewable energy sources for our requirement, which is depleting very fast in manner. And also these are the major cause of pollution [4]. So in order to reduce the above reason we are trying to incorporate renewable energy sources like solar wind tidal wave etc. These renewable sources are long term source of energy and first time investment cost is only significant as it has less running cost. The vehicle density is increasing day by day and because of drastic development in the transportation such as express, national highway, large amount of wind energy will be generated in the highway which can be effectively utilized by this proposed project. AERODYNAMIC ANALYSIS In this section, the wind turbine rotor design parameters are described as well as the model used to calculate its aerodynamic performance [5]. The wind turbine parameters considered in the design process are: Swept area Power and power coefficient Tip speed ratio Blade chord length Number of blades Initial angle of attack The swept area of the turbine determines the volume of air enclosed by turbine in its movement [7]. Depending upon the rotor configuration the shape of swept area will vary. In the case of HAWT swept area will be circular in shape, while for VAWT it has rectangular shape and is calculated using the formula: A= 2RL (1)

3 Design of Vertical Axis Wind Turbine for Low Wind Speed Application in Highway 13 Where A is the swept area [m 2 ], R is the rotor radius [m], and L is the blade length [m]. Swept area is the limiting factor for the volume of air which passes through the turbine. The turbine convert the energy from the wind contained in the swept volume of the turbine. So bigger the swept area, higher the power output for the same physical conditions [8]. The available power in wind for a vertical axis wind turbine can be found from the formula [9]: P w = ½ ρav 0 3 (2) Where V o is the velocity of the wind [m/s] and ρ is the air density [kg/m 3 ], the reference density used its standard sea level value (1.225 kg/m 3 at 15ºC). From the above equation we can observe that the power available in the wind is proportional to cube of the wind speed. The power the turbine takes from wind is calculated using the power coefficient: (3) C p value represents the part of the total available power that is actually taken from wind, which can be understood as its efficiency. There is a theoretical limit in the efficiency of a wind turbine determined by the deceleration the wind suffers when going across the turbine. For HAWT, the limit is 19/27 (59.3%) and is called Lanchester-Betz limit. The power coefficient consider the mechanical power conversion from energy available in the wind to turbine output only, it does not deal with the mechanical to electrical energy conversion, which includes the efficiency of generator [10]. The power coefficient is strongly dependent on tip speed ratio. TSR is defined as the ratio between the tangential speed at blade tip and the actual wind speed: TSR = R ω/ V 0 (4) Where ω is the angular speed [rad/s], R the rotor radius [m] and V o the ambient wind speed [m/s]. Each rotor design has an optimal tip speed ratio at which the maximum power extraction is achieved. The chord is the length between leading edge and trailing edge of the blade profile. The blade thickness and shape is determined by the airfoil used, in this case it will be a NACA airfoil, where the blade curvature and maximum thickness are defined as percentage of the chord [11]. The blade number has direct effect on the smoothness of operation of the turbine. Four and three bladed turbine are commonly used. The solidity σ is defined as the ratio between the total blade area and the projected turbine area [12]. It is an important non dimensional parameter which affects self-starting capabilities and for straight bladed VAWTs is calculated with σ = Nc/R (5) Where N is the number of blades, c is the blade chord, L is the blade length and S is the swept area, it is considered that each blade sweeps the area twice. This formula is not applicable for HAWT as they have different shape of swept area. Solidity determines when the assumptions of the momentum models are applicable, and only when using high σ 0.4 a self-starting turbine is achieved [13].

4 14 Lijin E M & Ashok S The initial angle of attack is the angle the blade has regarding its trajectory, considering negative the angle that locates the blade s leading edge inside the circumference described by the blade path. The main challenges of VAWT is the wide range of angle of attack the blade experience [14]. The initial angle of attack determines the self-starting capability of the turbine. With rise in rotational speed the maximum angle of attack decreases [15]. SIMULATION SETUP A simulation was done to compare the performance of different airfoils using Qblade software. The airfoil employs the NACA series foils NACA0012, NACA0015 and NACA The performance of the NACA series are compared through their Cl/Cd ratio. The airfoil configuration is illustrated in figure 1 SIMULATION RESULT Figure 1: The comparison of size and shape of NACA0012, NACA0015 and NACA0021 The analysis comprises of the lift(c l ), drag (C d ) and the lift to drag ratio. Figure 2: Comparison of C l /C d ratio Versus Angle of Attack for NACA0012, NACA0015 and NACA0021 In most case of turbine design the drag force is not desirable except in the case of drag type wind turbine such as Savonnius wind turbine. By comparing C l /C d ratio NACA0015 has higher C l /C d ratio. Here the angle of attack lies between 8 and15 degrees and C l /C d ratio is high for NACA0015 for this range of angle of attack. From the figure.1 it is clear that NACA0015 is the best solution for this purpose. A crucial factor for small turbine design is the low Reynolds range (< 1 million) in which they operate. Most studies in aerodynamics are performed for aircraft applications in which the Reynolds number lies above 3 million. It is very difficult and often impossible to find the right data for airfoils in this low Reynolds number range. For the NACA airfoils the maximum lift coefficient drastically decreases with decrease in Reynolds number. These effects can be seen in most types of NACA airfoils. For different airfoil the effect of Reynolds number is shown in figure.

5 Design of Vertical Axis Wind Turbine for Low Wind Speed Application in Highway 15 Figure 3: Effect of Reynolds number on C l /C d ratio for NACA0012 Figure 4: Effect of Reynolds number on C l /C d ratio for NACA0015 Figure 5: Effect of Reynolds number on C l /C d ratio for NACA0021 It is observed that the optimal angle of attack varies with the Reynolds number. And the drag to lift ratio also drastically decreases with decrease in Reynolds number. Most of the cases VAWT with fixed pitch blades is unable to start on itself. The main problem for Darrieus turbines is the negative power coefficient at low tip speed ratios. If the power coefficient is positive, the turbine is able to rotate independently and produce power. If the coefficient is negative, the turbine needs extra power to make it self-starting. A rotor blade was designed and simulated using the data from National Advisory Committee on Airfoils to test the power coefficient against tip speed ratio. Here in this case the tip speed ratio is less and the power coefficient is positive for the desired range, which means that the proposed prototype is self starting one.

6 16 Lijin E M & Ashok S Figure 6: Power Coefficient Versus Tip Speed Ratio Curve for Pitch Angle 0 and 1 Degree Figure 7 shows the three dimensional view of the proposed turbine. Here NACA0015 airfoil profile is used with three blades. Figure 7: Three Dimensional View of the Proposed Turbine DESIGN OF PMSG After identifying the characteristics of the turbine, the next step should be the determination of the necessary parameters to design the generators. Therefore, the design of generator-based on nominal values-will be carried out. Since the gearless structure of the turbine is taken into account, the rated speed of rotation of the blades will be considered as the synchronous speed. In addition, according to the basic design of generator, input torque should also be specified. To this end, transmitted torque in direct-drive wind turbine is expressed as: T w = J dw/dt +Dw +T w where Tw is the wind turbine torque, Tg is the input torque generator, ω is the angular velocity of rotation, D is the mechanical damping and J is the moment of inertia constant of both the rotor of the generator and the hub of the wind turbine. The machine is designed with maxwell RMxprt software. The design requirements of required machines are tabulated in table 1 Outer rotor PMSG is designed and its details are mentioned in [7] so just brief information about it will be given here. Optimization of PMSG is done aiming of low cogging torque which enables to generate electrical power even in low

7 Design of Vertical Axis Wind Turbine for Low Wind Speed Application in Highway 17 wind speed. In addition, magnet thickness, torque angle, flux density and efficiency optimizations are done. In design process, base speed is selected as 100 rpm. Table 1 Rated power 100w Rated speed 100rpm Base speed 90rpm Airgap length 1mm Cooling system Natural air Stacking factor 0.95 Figure 8: Flow Chart for Optimization of PMSG Figure 8 shows the flowchart followed for optimization of PMSG. In the first step, design requirements and constraints are introduced. In the next step, design parameters like characteristics of chosen material, winding parameters, etc are introduced. In this step, still the design variables are not assigned any value. Magnetic design is the first step after assigning the values to the air gap diameter and air gap flux density. Figure 9: Two dimensional geometry of PMSG

8 18 Lijin E M & Ashok S Figure 10: Three dimensional geometry of PMSG In order to determine the geometrical dimensions of the permanent magnets, the effective air gap (magnetic air-gap) should be assessed. It should be noted that the large air gap produces a sinusoidal flux density with low harmonic content. But in this case, by increasing the size of the permanent magnets, the weight and cost of the generator will increase. The two dimensional geometry and final geometry of PMSG is shown in Figure 9 and Figure. 10 CONCLUSIONS From the analysis of different air foils it can be concluded that the NACA0015 shows better perfomance compared to NACA0012 and NACA0021. The lift to drag force ratio for NACA0015 is higher than NACA0012 and NACA0021. The power coefficient for the rotor blade designed is found to be positive which indicate the designed three blade rotor is a selfstarting one. Here anlysis and design of permanent magnet outer rotor synchronous generator is also done in Maxwell RmXprt. Based on the finate element analysis it is observed that the increasing pole number of PMSG for same number of slot per pole per phase, electromagnetic torque is increased. REFERENCES 1. Sathyanarayanan, R., et al. "Highway windmill." Communication Software and Networks (ICCSN), 2011 IEEE 3rd International Conference on. IEEE, Abd Aziz, P. D., et al. "A simulation study on airfoils using VAWT design for low wind speed application." Engineering Technology and Technopreneuship (ICE2T), th International Conference on. IEEE, Islam, Mazharul, David S-K. Ting, and Amir Fartaj. "Aerodynamic models for Darrieus-type straight-bladed vertical axis wind turbines." Renewable and Sustainable Energy Reviews 12.4 (2008): McLaren, Kevin W. "A numerical and experimental study of unsteady loading of high solidity vertical axis wind turbines." (2011). 5. McLaren, Kevin W., Stephen W. Tullis, and Samir Ziada. "Vibration response behaviour of a high solidity, low rotational velocity, vertical axis wind turbine." ASME rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, Kedam, Naresh, et al. "Enhancement of Wind Turbine Aerodynamic Performance Using New Designed Airfoils." ASME 2015 Gas Turbine India Conference. American Society of Mechanical Engineers, 2015.

9 Design of Vertical Axis Wind Turbine for Low Wind Speed Application in Highway Chu, Chin-Chou, et al. "Unsteady flow past a two-dimensional airfoil undergoing large-amplitude pitching motion." 38th Aerospace Sciences Meeting and Exhibit. 8. Loganathan, Bavin, et al. "An experimental study of a cyclonic vertical axis wind turbine for domestic scale power generation." Procedia Engineering 105 (2015): Sharma, Shailendra, and Bhim Singh. "Performance Evaluation of Fixed-speed and Variable-speed Stand-alone Wind Energy Conversion Systems." Electric Power Components and Systems (2016): Li, Qing an, et al. "Analysis of aerodynamic load on straight-bladed vertical axis wind turbine." Journal of Thermal Science 23.4 (2014): Micha Premkumar, T., et al. "Numerical Studies on the Effect of Cambered Airfoil Blades on Self-Starting of Vertical Axis Wind Turbine Part 1: NACA 0012 and NACA 4415." Applied Mechanics and Materials. Vol Trans Tech Publications, Mehendale, Anant B., and Han Je-Chin. "Reynolds number effect on leading edge film effectiveness and heat transfer coefficient." International journal of heat and mass transfer (1993): Bragg, Michael B., Andy P. Broeren, and Leia A. Blumenthal. "Iced-airfoil aerodynamics." Progress in Aerospace Sciences 41.5 (2005): Li, Qing an, et al. "Analysis of aerodynamic load on straight-bladed vertical axis wind turbine." Journal of Thermal Science 23.4 (2014): Yamazaki, Wataru, and Yuta Arakawa. "Efficient Aerodynamic Shape Optimization of VAWT Airfoil and Its Validation." 33rd Wind Energy Symposium

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