This project is devoted to investigate the parameters that governs the efficiency of a wind turbine and to design blades capability of maximizing the energy generated from the turbine. Using the help of current technology, CAD virtual prototype of the design blade may be produced. The CAD design blade will undergo CFD analysis for the aerodynamic effect of the blade to produced sufficient force for optimum power output.
Keywords
Blade design parameter, CAD virtual prototype, CFD analysis, optimum energy production.
1. Introduction
1.1 Project Goal and Scope
The goal of this project is devoted to investigate the parameters that governs the efficiency of a wind turbine and to design blades capability of maximizing the power generated from the turbine. The Scope of this project is to design the CAD virtual prototype by using Solidwork 2008 software and then done the CFD analysis on the prototype by using Solidwork 2008 Cosmos Flow Work.
1.2 Problem Statement
Although there are currently many types and brands of wind turbine blade for energy production purpose offer in market, but none of it is design specifically suit for air velocity in Perlis. So this project is to design a specific wind turbine blade for wind velocity at Perlis in order to optimize energy production.
1.3 Project Overview
Wind machines were used long time ago; the first electricity generating windmill was built in the United Kingdom. It was a battery charging machine, which was installed in year 1887 by James Blyth at the location of Scotland. While the first utility grid-connected wind turbine also was built in United Kingdom by the John Brown Company in year 1954 at Orkney Islands.[1]
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The main function of wind turbines was design to exploit the wind energy which exists at a location, in another words, modern wind turbines is used to convert the existing wind energy to electrical energy. It is a system that comprises three integral components with distinct disciplines of engineering science. The rotor component includes the blades for converting wind energy to an intermediate low speed rotational energy. The generator component includes the electrical generator, the control electronics, and most likely a gearbox component for converting the low speed rotational energy to electricity. The structural support component includes the tower for optimally situating the rotor component to the wind energy source [1].
Wind turbines are classified due with their axis in which the turbine rotates, into horizontal axis and vertical axis wind turbines. Due to the ability to collect the maximum amount of wind energy for the time of day and season and to adjust their blades to avoid high wind storms; horizontal axis wind turbine are considered more common than vertical-axis turbines. Turbines that used in wind farms for commercial production of electric power these days are usually three-bladed and pointed into the wind by computer-controlled motors. This type is produced by the most common wind turbines manufacturers.
To design a wind turbine blade, there are several parameter need to be take consider. This parameter is such as the number of blade, tip speed ratio (TSR), blade radius, and wind speed and aerofoil profile. These parameter is important and must be determined before calculated the chord, twist and the angle of attack.
The development of the wind turbine blade can be design by using Autocad and Solidwork. By comparing this two CAD software, Solidwork is more advance due to its capability of 3D modelling is more easier.
To perform the comparison of the wind turbine blade, a test to study the performance of the wind turbine blade needs to be performed. Since we cannot actually build out the wind turbine for studying it performance, so the Solidwork 2008 Cosmos flow work is required to analysis the wind turbine's performance.
Literature Review
Wind energy is the faster growing renewable energy source. In the future renewable energy derives such as wind turbines are playing a significantly increasing role in the generation of electrical power. The turbines fall into two types: horizontal axis wind turbines (HAWT) and vertical axis wind turbines (VAWT), by the name suggest, turbines differ in the position of the axis.
In previous, there are several optimization techniques of blades design had been used in designing an efficiency blade. In my point of view the most completed and developed method is introduced by Danish experts P. Fuglsang and H.A. Madsen from the Danish National Institute RISO. They have been engaged in the design process and in the optimization of wind energy use for many years. In their works [9], they divide the design process for the following components:
Block of initial data. Set the goal function, input parameters, limitations and preliminary design options; wind conditions and structural model of the wind turbine.
Calculation block. Provides estimations of output parameters of wind turbine for given initial data. This unit will include consideration of operational (noise, power, mechanical loads) and design (economic) parameters.
Design block. Makes changes in the input design data and provides an optimized variant.
Rotor Concepts
Wind turbines are energy conservation devices used to harness the power of wind for electricity generation. The primary component of a wind turbine is the rotor. The rotor transforms the kinetic energy of moving air into mechanical energy, where it will then be converted into electric power. The ability of the rotor to convert a maximum proportion of wind energy flowing through the swept area into mechanical energy is depending on the aerodynamic properties.
Wind direction
Blade Rotor
Swept area
Figure 1: Swept area of a Horizontal axis wind turbine
There are two types of rotor concepts for horizontal axis wind turbines, upwind and downwind. A downwind configuration allows the rotor to have free yawing and it is simpler to implement than active yawing which requires a mechanism to orient the nacelle with the wind direction in an upwind configuration. Both upwind and downwind configuration can have one, two, three or even more blades and selection of the number of blades is a trade-off among three different points of view that are discussed below:
Operation point of view
Despite higher moment of inertia of three bladed rotors, the main advantage of them is that the polar moment of inertia with respect to yawing is constant while for a two bladed rotor it varies with azimuthal position with the highest amount when the blades are horizontal and the lowest when they are vertical [2]. This phenomenon contributes to a smooth yawing of three bladed rotors and an imbalance for two bladed rotors. To overcome this problem a teetering hub can be used for two bladed rotors that can lessen this effect when the nacelle yaws [3].
Structural design point of view
There is a coupling between tip speed ratio, number of blades and rotor solidity. To be optimum, a high speed ratio rotor should have less blade area than the rotor of a slower turbine. For a given number of blades the chord and the thickness decrease as the tips speed ratio increase and these results in an increase in blade stresses [4]
Performance point of view
In general the optimum tip speed depends on the number of blades and profile type used [5].
Tip Speed Ratio
Cp
Figure 2: Effect of number of blades on power
Performance [2]
The fewer the number of blades, the faster the rotor needs to turn to extract maximum power from the wind. Three bladed rotors have a higher achievable performance coefficient which does not necessarily mean that they are optimum. Two bladed rotors might be a suitable alternative because although the maximum Cp is a little lower, the width of the peak is higher and that might result in a larger energy capture. To achieve this goal a variable speed rotor can be used [2].
2.2 Wind turbine aerodynamic
2.2.1 Aerofoils
An aerofoil is a body with a shape similar to that shown in Fig.3 the mean chamber line is the locus of point halfway between the upper and lower surfaces of the aerofoil. The cord length, c, is the distance from the leading to the trailing edge. The angle of attack, α is defined as the angle between the relative wind direction and the chord line. Aerofoils create a lifting force in a fluid flowing from a specific range of angles of attack. The flow velocity is higher over the convex surface resulting in lower average pressure on that side of the aerofoil compared with high pressure on the bottom side of the aerofoil. Friction also occurs between the fluid and the aerofoil surface. The result is lift forces and a pitching moment, this moment acts at a distance of c/4 from the leading edge. (Fig 4).
Mean chamber Line
Halfway between top and bottom
Figure 3: Typical aerofoil body shape [6]
Figure 4: Pressure distribution [6]
Flow characteristic of aerofoils can be described by non-dimensional parameters. The most important parameter is the Reynolds number, Re defined by Eq.1 where,µ is the fluid viscosity, v is the kinematic viscosity. V and c describe the scale of the flow.
(1)
Other important coefficients are the two-dimensional lift coefficient, (Eq. 2), while the drag coefficient, (Eq.3) are shown as below:
(2)
(3)
2.2.2 Chord length
Chord length is subjected to wind turbine rotor diameter, blade numbers located on the rotor and rotor end speed rate (Piggott 2006).
(4)
Where, C is the cord length, D is the rotor diameter, λ is the tip speed ratio and b is the number of blade.
2.2.3 Tip speed ration λ
Tip-speed ratio is the ratio of the speed of the rotating blade tip to the speed of the free stream wind. There is an optimum angle of attack which creates the highest lift to drag ratio.
Because angle of attack is dependent on wind speed, there is an optimum tip-speed ratio.
(5)
Where,
Ω = rotational speed in radians /sec
R = Rotor Radius
V = Wind "Free Stream" Velocity
Figure 5: Parameter of tip speed ratio
2.2.4 Angle of attack
The angle of attack, or angle between the chord line and the relative velocity, is calculated by this expression:
(6)
Where,
is the flow angle
is the twist of the blade
is the pitch angle
Figure 6: Flow around section of a wind turbine blade
2.2.5 Twisting angles
There are some important angles in blade design, which is been listed as below:
1. The angle of attack is the angle between the profile's chord line and the direction of the airflow wind.
2. The flow angle is the angle between the relative velocity and the rotor plane.
3. The pitch angle p is the angle between the tip chord and the rotor plane.
4. The twisting angle, which is the angle measured relative to the tip chord. We can calculate this value using the Eq.6
It is important to find out the optimum twisting angle, because a rotor blade will stop providing enough lift once the wind hits the blade at a steeper angle of attack. The rotor blades must therefore be twisted to achieve an optimal angle of attack throughout the length of the blade.
3.0 Methodology
Figure 7: Methodology of the project.
The project is started by doing the literature review. The related affected parameters in been study in this section. After that some reference data is collected by the flow analysis on the blade design with 3 types of NACA aerofoil profile series. After the data collected, some theoretical calculation and judgement are make. With the judgement maked, a initial design is make and after that Solidwork 2008 cosmos flow work is used to done a flow analysis on the initial design. With the data collected form the analysis, a comparison is make, and based on this data, a redesign is make. These step keep repeating until an optimum design is occur.
4.0 Project progress
Figure 7: Gantt Chart
4.1 Result
4.1.1 Aerofoil Profile used in the Design
Figure 8: NACA 0012 aerofoil Profile.
Figure 9: NACA 4412 aerofoil Profile
Figure 10: NACA 4415 aerofoil Profile
In this project, the blade optimizing process will be done in 3 type of aerofoil profile blade. Several parameters will be set and test on the selected aerofoil profile in order to find out the optimum design of the turbine blade for optimizing energy production purpose.
4.1.2 Effect of Blade Length
Blade Length (R)
Figure 11: CAD drawing for the wind turbine blade
In this section, the wind turbine blade is been design and tested on its efficiency ratio according to different blade length.
The range of the blade is set as 15m- 20m which is calculate from the equation of power:
(7)
Where,
P is the desired output power (100kW)
is the coefficient of performance (0.45)
is the Mechanical/ electrical efficiency (0.9)
R is the blade length
V is the nominal wind speed. (7 m/)
Ï is the air density (1.226 kg/)
Figure 12: Pressure distribution and streamline on NACA 0012
Lift Force
Drag Force
Figure 13: Pressure distribution and streamline on NACA 4412
Lift Force
Drag Force
Figure 14: Pressure distribution and streamline on NACA 4415
Figure 1: Comparisons of efficiency ratio of NACA 0012, NACA 4412, and NACA 4415 based on different blade length.
By comparing the efficiency ratio of the wind turbine blade, the most efficiency aerofoil profile due to the effect of radius length is NACA 4412 with blade length 20m
Conclusion:
Based on the tested result on the effect of blade length, wind turbine blade design with NACA 4412 aerofoil profile is the most optimum design among all of the tested length. In the future improvement, the design will be tested on the effect of angle of attack, twisted angle, chord length, and tip speed ratio towards the efficiency ratio.
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