Wind Turbine Intro And Eveythong.pdf

CHAPTER 1 INTRODUCTION 1.1 Background of the study For human development to continue, it is a must to find new sources of renewable or virtually inexhaustible energy. In the present scenario the growing demand for energy is one of supply that has never been able to match, it is incalculable. Energy demand plays a very important role in these generations, due to the economic growth, the energy demand of the world increase every year. Continuous usage of energy results in a quick depletion of the fossil fuel which is the primary source of energy in these days. In the energy conversion process in power plants and small engines, energy efficiency is a key factor because the equipment with higher efficiency have more work output. The constant search for new and viable energy sources has led to a discovery about an alternative source of energy which is renewable energy sources such as solar and wind energy which can help substitute the fossil fuel. Nowadays lot of countries continually use wind energy for power generation, as it is one of the feasible renewable energy sources. The wind force can be very strong, as what we’ve seen in the aftermath of a typhoon or a cyclone as it damages the infrastructures. In early times, people have harnessed wind energy as means of using the sails of the ship. Wind Energy is a viable industry that has become a valuable energy source. The energy generated from wind is clean and efficient. The wind energy industry helps to ensure that electric demands are met, wildlife impact is minimal, the environment is not devastated, as well as creates new jobs during 1

the construction of wind farms, daily operations, manufacturing components, and exporting components to foreign countries. Wind has been used in windmills to grind grain or to pump water for irrigation. Small scale wind turbines should reliable, affordable and almost zero maintenance. In a large scale wind turbines, a generator will be used as a motor to start and accelerate the rotor and produce power. Windmills now in the form of wind turbines have been used for millennia to convert the wind’s kinetic energy into mechanical energy. Throughout the 20th century parallel paths developed small wind plants suitable for farms or residences, and larger utility-scale wind generators that could be connected to electricity grids for remote use of power. Today wind powered generators operate in every size range between tiny plants for battery charging at isolated residences, up to near-gigawatt sized offshore wind farms that provide electricity to national electrical networks. In recent years, wind energy has become one of the most economical renewable energy technologies. Today, electricity generating wind turbines employ proven and tested technology, and provide a secure and sustainable energy supply. At good, windy sites, wind energy can already successfully compete with conventional energy production. Many countries have considerable wind resources, which are still untapped. Following the recent developments in renewable energy sources, wind turbines have been one of the primary devices focused on. Basically, wind turbines are devices that convert the kinetic energy from the wind into electrical power for human usage. “Wind farms” are created in very windy places to harness this energy. It is however impossible to harness the entire 2

power potential from the wind. Only 59% of the total kinetic energy of the wind flowing in the turbine can be harnessed. Efficiency greatly depends on the maintenance of the wind turbine and its components. 1.1.1 Historical Review of Wind Energy It was centuries ago when the technology of wind energy made its first actual steps although simpler wind devices date back thousands of years ago with the vertical axis windmills found at the Persian-Afghan borders around 200 BC and the horizontal-axis windmills of the Netherlands and the Mediterranean following much later (1300-1875 AD). (Pasqualetti MJ, et.al. 2004) Further evolution and perfection of these systems was performed in the USA during the 19th century, i.e. when over 6 million of small machines were used for water pumping between 1850 and 1970. On the other hand, the first large wind machine to generate electricity (a low speed and high-solidity wind turbine (WT) of 12 kW) was installed in Cleveland, Ohio, in 1888, while during the late stages of World War I, use of 25 kW machines throughout Denmark was widespread. Further development of wind generators in the USA was inspired by the design of airplane propellers and monoplane wings, while subsequent efforts in Denmark, France, Germany, and the UK (during the period between 1935 and 1970) showed that large-scale WTs could work. European developments continued after World War II. In Denmark, the Gedser mill 200 kW three-bladed upwind rotor WT operated successfully until the early 1960s, while in Germany, a series of advanced horizontal-axis designs were developed, with both of the aforementioned concepts dictating the future horizontal- axis design approaches later emerging in the 70s. (Meyer NI, 1995) 3

New ways of using the energy of the wind eventually spread around the world. By the 11thcentury, people in the Middle East used windmills extensively for food production. Returning merchants and crusaders carried this idea back to Europe. The Dutch refined the windmill and adapted it for draining lakes and marshes in the Rhine River Delta. When settlers took this technology to the New World in the late 19th century, they began using windmills to pump water for farms and ranches and later to generate electricity for homes and industry. The first windmill for electricity production is built by Professor James Blyth of Anderson's College, Glasgow (now Strathclyde University). The professor experiments with three different turbine designs, the last of which is said to have powered his Scottish home for 25 years. (Wind Energy Foundation, 2018) HISTORY OF WIND TURBINE

Fig. 1 (courtesy: clean future.co)

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1.1.2 Categories of Wind Turbine There are two categories of wind turbines: the horizontal axis design (HAWT) and the vertical axis design (VAWT) as shown in figure 1.1. The most commonly used turbine in today's market is the horizontal-axis wind turbine. Since it is the more practical and popular, the HAWT enjoys more attention than VAWT. The HAWT (see fig.1) has its main rotor shaft at the top of the column along with the electrical generator. The turbines must be pointed into the wind and is positioned favorably by either a small weathervane or a wind sensor. The amount of power a horizontal-axis turbine will produce is determined by the diameter of its rotor. The diameter of the rotor defines its "swept area," or the quantity of wind intercepted by the turbine. The turbine's frame is the structure onto which the rotor, generator, and tail are attached. The rotor shaft and gearbox of the VAWT (see fig. 1) are positioned vertically and are also installed near the ground. This makes it more accessible for maintenance and other necessary adjustments. One of the reasons why this type of wind turbine is less popular is that it can produce what is known as pulsating torque. Vertical-axis wind turbines consist of two types: Savonius and Darrieus. A Savonius turbine (see fig.1.2) can be recognized by its "S" shaped design when viewed from above. Darrieus turbines (see fig.1.3) look like an eggbeater and have vertical blades that rotate into and out of the wind. It is a type of wind turbine where the main rotor shaft is set transverse to the wind (but not necessarily vertically) while the main components are located at the base of the turbine. This arrangement allows the generator and gearbox to be located close to the ground, facilitating service and repair. VAWTs do not need to be pointed into the wind which removes the need for wind-sensing and 5

orientation mechanisms. Horizontal-axis turbines convert more of the wind’s energy into useful mechanical motion because the blades are perpendicular to wind direction, and the blades pick up the energy throughout their range of movement. By comparison, the blades on a vertical-axis turbine suffer an efficiency disadvantage, capturing energy from the wind only on the front side; at the rear part of their rotation, they drag on the system.

That’s why in this

study, it is more efficient to use HAWT. (Abas, M.F., 2006)

Fig. 1.1. HAWT (left), VAWT (right) (source: Hughes, K. 2008)

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Fig. 1.2. Savonius wind turbine (source: NW Wind & Solar, 2016)

Fig. 1.3. Darrieus wind turbine (source: Aggeliki K, 2011)

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1.1.3 Wind Turbine Blade Wind turbine blades have been fashioned in many different configurations and wind turbines themselves operate according to different philosophies depending at least to some extent on the use to which the turbine is put. The blade figure plays a big role in a wind turbine as it increases or decreases the efficiency of the turbine and twisting it will theoretically increase its harvested wind. Because of the aerodynamic design of the blades you can notice that the blades start rotating very slowly and then begin accelerating faster and faster. Wind turbines are commonly used to generate electricity, and can be connected directly or indirectly to a generator. It is often desired to generate current at a predetermined frequency, and direct connection then requires either that the turbine be operated at constant speed, or that a variable frequency output be converted in for example a static converter to a fixed frequency. The blades of a wind turbine are shaped similar to an airplane wing, with one side (rear) much more curved than the other (front). With a wing, air flows fastest over the top which reduces the pressure and causes the lift needed for the aircraft to fly. Turbine blades also rely on pressure differentials due to changes in air speed in order to operate. When the wind begins blowing and passing over the blade, air behind the blade starts travelling at a higher velocity than air in front of the blade. In fact, the greatest velocity is at the rounded front edge which creates a pocket of low-pressure air. This literally pulls the blade forward and we get the start of rotation. Once the blades are rotating, they create their own headwinds (like what we feel on our face when cycling). The velocity of this additional wind 8

helps to lower the pressure on the back side of the blade and contributes to even more lift. This causes the blade to rotate faster and produce additional headwind. The net effect is that the blades of a turbine spin more rapidly until they reach their maximum velocity. (Megraw, 2012). 1.1.4 Generating Energy from wind Wind is created by the unequal heating of the Earth's surface by the sun. Wind turbines convert the kinetic energy in wind into mechanical power that runs a generator to produce clean electricity; wind rotates the turbine to generate electricity. The rotor blades on a wind turbine catch the kinetic energy in the wind and transfer it via a rotor shaft to the generator. The wing blades can be rotated and adjusted to the wind direction and strength, for maximum utilization of energy. When the rotor spins, the power is transferred via the drive shaft and gearbox. Then, the generator converts the kinetic energy from the turbine into electrical energy. The electricity is sent to the substation, where it is converted and then transported out on the net. (DOE, 2018) 1.1.5 Twisted Blade Modern wind turbine blades have a twist along the length of the blade. The airfoil's optimal angle of attack is affected by the apparent wind direction. The apparent wind direction changes as the speed of blade increases, even when a uniform wind velocity exists across the rotor swept area. As the tip of the blade travels much faster than segments of the blade closer to the hub of the rotor, the blades have incorporated a twist as to achieve an optimal angle of attack along the full length of the turbine blade.

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A lifting force is generated due to the curved shape of the blades just as in case of an airplane wing. A low air pressure is created on the side with most curves, while the high pressure created beneath pushes the other side of blade aerofoil. This results in generation of a lift force that is perpendicular to the air flow direction. The rotor blade also needs to be designed appropriately to generate the right amount of rotor blade thrust and lift to produce the exact amount of deceleration of air. The twist closer to the tip of the blade, the faster the blade is moving through the air and so the greater the apparent wind angle is. The blade needs to be turned further at the tips than at the root, in other words it must be built with a twist along its length. The requirement to twist the blade has implications on the ease of manufacture. (Peters, 2013)

Fig. 1.4. Image credit: Murdoch University

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1.1.6 Conceptual Framework

Airfoil selection Designing(solidworks) Simulation (CFD) Fabrication of design

Conclusions/ recommendations

Modification Experimental set-up BEM (calculations)

1.2 Statement of the Problem This study seeks to answer the following questions: 1. What is the importance of airfoil selection when designing a wind turbine? 2. What is the effect of twisting the blade? 3. Why does the wind speed affect the over-all performance of wind turbine? To answer the above questions, this study required the simulation results from CFD in solidworks and the fabrication of blades to optimize the maximum power output to be generated.These fabricated blades will then be tested in a wind tunnel with a different velocity. In order to conclude that the designed blade is at its best, it will be compared to the 3 base blades which are the normal blade, twisted blade and twisted NACA 4412. The null hypothesis to be tested in the study are the following: 1. The airfoils are an important part of the design. The airfoil shape is in charge of generating lift by taking advantage of the Bernoulli Effect. Even minor changes in the airfoil can greatly affect the power output and noise produced by the turbine as the results display with the modifications done in the baseline turbine. 11

2. The blades rotate, the tip moves faster than the hub. So to make the blades efficient, the blades are twisted, angle of attack of the blades at the tip is lower than at the hub because it is moving at a higher velocity than the hub. 3. Wind speed determines the amount of electricity generated by a turbine, thus, modifying the aerodynamic performance of the aerofoil blade is so challenging to obtain results that might be of use for small-scale applications. 1.3 Objectives of the Study The main purpose of this study is to evaluate the performance of SD 7032 airfoil,

to aerodynamically design, optimize twist angle distribution and pitch

angle using CFD to produce more power. But before that, the following issues were considered: Study the effect of twist and pitch on the performance of a small-scale

 HAWT. 

Study the effect of external forces for power generation.



The angle of attack to be considered for twist distributions.



The equipment and location used for this study.

1.4 Significance of the Study This study aims to expand the knowledge of St. Peter’s College students specifically the Mechanical Engineering students in the area of Wind Power Technology sharing thru community extension services which the department is currently limited and inadequate and further more it can be used as a reference to innovate the recent technologies for generating wind power.

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1.5 Scope and Limitation 

The blade design is limited to the blade geometry and fabrication is limited to available resources (equipments and instruments) and experiment shall be done at SPC Mechanical Shop.



The blade design is based on untwisted blade SD7032 only and will be modify into a twisted blade.



This study focuses on the right angle of attack, blade design, and the twisted blade will be compared to the 3 base blades that were fabricated in FABLAB Mindanao located at MSU-IIT.

1.6 Theoretical Framework 1.6.1 Blade Element Theory The Betz law explains that some of the wind needs to move through the turbine blades in order to make room for the next amount of wind coming in. If 100% of the power would be harnessed, no more could be contained and converted. Betz scientifically calculated that only 59% of the power in the wind can be successfully captured and converted. This means that just over half of the power available to us is being converted and is available for use. Betz's law calculates the maximum power that can be extracted from the wind, independent of the design of a wind turbine in open flow. It was published in 1919, by the German physicist Albert Betz. The law is derived from the principles of conservation of mass and momentum of the air stream flowing through an idealized "actuator disk" that extracts energy from the wind stream. According to Betz's law, no turbine can capture more than 16/27 (59.3%) of the kinetic energy in wind. The factor 16/27 (0.593) is known as Betz's coefficient. 13

Practical utility-scale wind turbines achieve at peak 75% to 80% of the Betz limit. (Betz, 1966)

1

P = ρAV3∞ ⋅ 2

16

(eq. 1)

27

Where: ρ= Density of air (kg/m2) A= Swept area (m2) V∞= Velocity force (Newton) 1.6.2 Reynolds Number Reynolds number is a dimensionless quantity that is used to help predict similar flow patterns in different fluid flow situations. ρ

V=μ

Re =

(eq. 2) Cm V

Where:

(eq. 3)

ν

V = Velocity of the fluid (mps) μ = viscosity of fluid (mPa) ν = the kinematic viscosity of the fluid (m2/s)

Cm = the characteristics length, the chord width of an airfoil (m)

1.6.3 Swept Area

The swept area is the plane of wind intersected by the generator. As such, the height of the blades times the diameter of rotation will produce the square meters or feet of the swept area. It is the area though which the rotor blades of a wind turbine spin, as seen when directly facing the center of the rotor blades. 14

The power output of a wind turbine is directly related to the swept area of its blades. The larger the diameter of its blades, the more power it is capable of extracting from the wind. The larger the blades, the stronger they need to be withstand the higher levels of centrifugal and cyclic varying gravitational loads. (Molaeb, 2011) A = πr2

(eq. 4)

Where:

r = Swept radius (m)

Fig. 1.6. wind turbine 1.6.4 Planform Area The planform area of a wing is the area of a wing as if it were projected down onto the ground below it. (Everything2, 2002) (eq. 5)

AT = Cm xb

Where:

Cm = Average cord length (m) b = Blade length (m)

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1.6.5 Aspect Ratio Aspect Ratio is the ratio of its sizes in different dimensions. Blade’s aspect ratio is equal to its span over the average chord length. (Kermode, 1972) Cm = CN + … + CN+1

(eq. 6)

b

(eq. 7)

AR = Cm Where: Cm = Average cord length (m) b = Blade length (m)

1.6.6 Lift and Drag Coefficient The lift coefficient (CL) is a dimensionless coefficient that relates the lift generated by a lifting body to the fluid density around the body, the fluid velocity and an associated reference area. A lifting body is a foil or a complete foil-bearing body such as a fixed-wing aircraft. CL is a function of the angle of the body to the flow, its Reynolds number and it’s Mach number. The lift coefficient c1 refers to the dynamic lift characteristics of a two-dimensional foil section, with the reference area replaced by the foil chord. (Clancy, 1975) CL = Where:

2FL

(eq. 8)

ρV2 AT

FL = Lift Force (Newton)

Ar = Planform Area (m2) V = Velocity (mps)

ρ = Density of air (kg/m2) 16

The drag coefficient (Cd) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water. It is used in the drag equation, where a lower drag coefficient indicates the object will have less aerodynamic or hydrodynamic drag. (McCormick, 1979) . The drag coefficient is always associated with a particular surface area. The drag coefficient of any object comprises the effects of the two basic contributors to fluid dynamic drag: skin friction and form drag. The drag coefficient of a lifting airfoil or hydrofoil also includes the effects of lift-induced drag. (Clancy, 1975) CD = Where:

2Fd

(eq. 9)

ρV2 AT

FD = Lift Force (Newton) Ar = Planform Area (m2) V = Velocity (mps)

ρ = Density of air (kg/m2)

1.6.7 Tip-speed Ω=N

2πr

(eq. 10)

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Where: N = rotational speed (rpm) r = radius (m) 1.6.8 Tip Speed Ratio =

Ω

(eq. 11)

U

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Where: Ω = Blade tip speed (mps) U = Wind Speed (mps)

1.6.9 Local tip-speed ratio for the ith blade element r,i =  (ri/ R)

(eq. 12)

Where:  Tip Speed Ratio ri = ith radius (m)

R = Overall Radius (m) 1.6.10 Optimum relative wind angle for the ithblade Ɵopt,i=

2

tan-1 (1 / r,i)

(eq. 13)

Ɵopt,i=

2

tan-1 (1 / r,i)

(eq. 14)

Where:

3

3

r,i= Local tip-speed ratio for the ith blade element 1.6.11 Twist distribution for the ithblade iƟopt,i- 

(eq. 15)

Where: Ɵopt,i= Optimum relative wind angle for the ithblade(degrees) angle of attack (degrees)

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1.7 SD 7032 airfoil SD7032 is an asymmetric, low Reynolds number airfoil with a maximum thickness of 10% and a maximum camber of 3.4% at 26.6% and 45.1% chord length respectively, measured from the leading edge. The profile of the Selig/Donovan, SD7032 airfoil with the points of maximum relative thickness and maximum camber as shown in Figure 1.7

Fig.1.7: SD-7032 airfoil profile with 10% relative thickness 1.8 Definition of Terms

Fig.1.8. airfoil parameters

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

Angle of attack: is the angle between the reference line of a body and relative wind. On an airfoil such as one on a wind turbine, it is the angle between the chord line and the relative wind vector. (Hall, 2018)



Chord Length: the distance between the trailing edge and the point on the leading edge where the chord intersects the leading edge. (Houghton, 2003)



Leading edge: It’s the point at the front of an airfoil, which has the maximum curvature. (Crane, 1997)



Chord Line: It’s the straight line that connects the leading edge and trailing edge of an airfoil. (Wikipedia, 2015)



Trailing Edge: It’s the point at the rear of an airfoil, which has the maximum curvature. (Crane, 1997)



Mean Camber Line: A line joining the leading and trailing edge of an airfoil from the upper and lower surfaces. The mean camber line determines the characteristics of the airfoil. (Illustrated Dictionary of Aviation, 2005)



Tip Speed Ratio: Tip speed ratio is the most commonly and conveniently used scaling parameter, which integrates the principle aerodynamic effect of the wind speed, rotor size and rotor’s angular speed with the power coefficient of the wind turbine rotor. It evaluates the tangential speed of the turbine’s blade with respect to the free wind speed (Duquette et al 2003).



Cut-in Speed: The cut-in speed of a wind turbine is defined as the minimum wind speed at which the wind turbine starts on its own and generates some usable power. 20



Rated Speed: The rated speed of a wind turbine is defined as the minimum wind speed at which the wind turbine generates its indicated rated power.



Cut-out Speed: The cut-out speed of a wind turbine is the maximum wind speed up to which the wind turbine should operate. This is required as a safety feature to protect the wind turbine from being damaged at the high wind speed.

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CHAPTER II REVIEW OF RELATED LITERATURE 2.1 Twist angle The lift generated by an aerofoil section is a function of the angle of attack to the in flowing air stream (Section 5.4). The inflow angle of the air stream is dependent on the rotational speed and wind speed velocity at a specified radius. The angle of twist required is dependent upon tip speed ratio and desired aerofoil angle of attack. Generally the aerofoil section at the hub is angled into the wind due to the high ratio of wind speed to blade radial velocity. In contrast the blade tip is likely to be almost normal to the wind.

The total

angle of twist in a blade maybe reduced simplifying the blade shape to cut manufacturing costs. However, this may force aerofoils to operate at less than optimum angles of attack where lift to drag ratio is reduced. Such simplifications must be well justified considering the overall loss in

turbine

performance. 2.2 Blade Shape Summary An efficient rotor blade consists of several aerofoil profiles blended at an angle of twist terminating at a circular flange (Figure 2.2). It may also include tip geometries for reducing losses. To facilitate production, several simplifications maybe made by: 

Reducing the angle of twist.



Linearization of the chord width.



Reducing the number of differing aerofoil profiles. 22

As Burton et al. (2011) stated “a successful blade design must satisfy a wide range of objectives too, some of which can be in conflict” (p. 377). These objectives are the followings: 1. maximize annual energy production; 2. restrict the maximum power output in the turbine 3. endure fatigue loads; 4. limit tip deflections to avoid blade and tower collisions; 5. prevent resonances and 6. overall, minimize weight and cost. Burton et al. (2011) also affirmed that: The design process can be divided into two stages: the aerodynamic design, in which objectives (1) and (2) are satisfied, and the structural design. The aerodynamic design addresses the selection of the optimum geometry of the blade, the external surface, also referred as the blade geometry. The blade geometry is defined by the airfoil family and the chord, twist and thickness distribution. The structural design consists of blade material selection and determination of a structural cross section or spar within the external envelope that meets objectives (4) to (6). (p. 377). The two stages are intrinsically linked, as the blade thickness needs to be large enough to accommodate a spar which is structurally efficient. The focus on this study is to improve only the blade geometry through the different design case studies of the parameters within.

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2.2.1 Design Angle of Attack As for the design angle of attack, generally, a high lift (which contributes most to positive torque) and a low drag (which contributes most to thrust and cause negative torque) are preferable for maximum power coefficient design of wind turbine blades, thus the design angle of attack is often selected at the critical angle of attack where the lift to drag ratio (cl/cd) is maximum. For this blade design case, the design angle of attack is set at the critical angle of attack 8°. 2.2.2 Airfoil Characteristic For wind turbine blade design and analysis, it is essential to have the aerodynamic data of the selected airfoil at the corresponding flow conditions, i.e. Reynolds (Re) numbers. The Reynolds number is defined as:

Where:

Re =

Cm V

(1)

ν

V = Velocity of the fluid (mps) μ = viscosity of fluid (mPa) ν = the kinematic viscosity of the fluid (m2/s)

Cm = the characteristics length, the chord width of an airfoil (m) 2.4 Twist distribution Choosing the twist distribution is the least controversial design parameter to be selected according to Schubel and Crossley (2012). In most cases, the full length of the blade is twisted through the hub to the tip to change the blade angle that increases the lift and prevents over speed of the rotor. Exceeding 24

the rotor speed may lead to a catastrophic failure under excessive load or the overload of the generator. Gurit (2013) affirmed that “close to the tip of the blade is where the faster the blade is moving through the air, so the largest the wind angle is. Thus the blade needs to be turned further at the tips than at the root it must be built with a twist along its length”(p.6) as it is shown in Figure 2.1. Typically the twist is around 10-20º for large HAWT, in the case of the hand-made small wind turbines like the Peruvian, the twist distribution goes from 14º to 2º. The requirements to twist the blade have implications on the difficulty of manufacture.

2.5 Blade Chord and Twist Angle Distributions In the standard BEM method, if the Cp of each section along the blade span is at its maximum, the maximum power coefficient of the whole blade is achieved. Referring to equations of the standard BEM method. The sectional power coefficient is expressed as: F sin 2  cos    r sin  (sin    r cos  ) r [1  C d / C d  cot  ]  Max (2) 2

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Where: F= is the tip-hub loss factor

 = relative angle of attack in rad r= local tip speed ratio Cd/Cl= drag to lift ratio Ignoring the tip-hub loss and drag effect, i.e. F is equal to 1 Cd/Cl is equal to zero, with the partial derivative of the main part being zero, the optimum twist angle is obtained. In the standard BEM method, the following equations are often used to calculate the optimal blade chords and twist angles: Φr=

2

tan-1 (1 / r,i)

(3)

Cr 

8r (1  cos  r ) ZC l

(4)

3

where, r= is local radius in m, Φr= is the local relative angle of attack in rad r= local tip speed ratio Cr= is the local chord in m 2.5.1 Blade Pitch and Twist Study The pitch and twist angles are very important parameters which have a considerable effect on the power production of wind turbine rotor blades. The twist angle decides on the values of the local angle of attack. Twisted blades for wind turbines have been proved to be superior to the untwisted ones due to their full utilization of the blade area to produce lift at low drag. The twist angle is defined in Fig.2.2. 26

Figure 2.2: The pitch and twist angles Where Vt is the tangential velocity, Vz is the axial velocity and Vrel is the relative velocity. The angles appearing in Fig.2.2 are defined as follow:

α: is the angle of attack defined as the angle between the chord line



and the relative velocity. 

Φ : is the flow angle defined as the angle between the relative velocity

and the plane of rotation. 

θ

: is the local pitch angle defined as the angle between the local

airfoil chord line and the plane of rotation. In fact

is called the local pitch angle which is a combination of the pitch angle

θp and the twist angle β: θ = θv+β

(5)

Where the pitch angle is the angle between the tip chord line and the plane of rotation and the twist angle is measured relative to the tip chord line. The pitch angle is constant and it is added to the varying twist angle along the blade span. In particular it is possible to use the twist to influence the flow separation and stall at a certain wind speed. For this reason, the fixed pitch rotor blades are not linearly twisted. The twist angles towards the root are greater than the 27

angles towards the tip. This variation in twist is determined by both the stall characteristics and the starting torque The effect of different blade twist variations on the power production of the blade can be seen in Fig.2.3. It is clear that non-twisting the blade results in considerable reduction in power. The advantage of untwisted blades is the easy and low cost manufacturing. However, since the modern blades are mostly manufactured in molds and made of fiber glass, manufacturing became also easy for twisted blades. The profit of the more energy produce by twisted blades is more than the price difference of manufacturing untwisted blades.

Figure 2.3: Effect of blade twist on the blade power coefficient

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CHAPTER III METHODOLOGY The present work was performed in the following steps: 

Selection of airfoil to be modified



Design of the model using CFD (Solidworks)



Fabrication of blades using the 3d printer in FABLAB Mindanao



Performing the wind tunnel experiments



Data Analysis

3.1 Conceptual Design Through the use of Solidworks simulation, SD7032 was then simulated from 4° to 10° to get the best angle of attack with a wind velocity of 4.5m/s. From the simulation results, the highest lift-to drag ratio (Cl/Cd) was chosen and is used to get the optimum relative wind angle to be used in designing the twist distributions along the sectioning of the blade through the use of equations from the relative studies. 3.2 Geometry of Twist Distribution SD7032 was used as the blade profile for this design. Having a blade length of 300mm and a chord length of 100mm. Using Solidworks, the blade length was then divided into 10 sections, This modification has been performed such that twist distribution of the blade has been linearized. Using (eq.12) and (eq.13), the blade’s ith radius were calculated same as to the Optimum relative wind angle for the ithblade. From the results of this calculation,

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the twist distribution per section was obtained and is used for designing the twisted blade. 3.3 Determining the best angle of attack through Solidworks simulation.

Wind speed

4°

5°

6°

7°

8°

9°

10°

5m/s

5.785

5.496

7.565

5.579

5.989

5.392

5.576

6m/s

6.051

5.971

7.748

5.6212

6.255

5.609

5.623

Table 3.1: SD 7032

simulation reports

Fig. 3.2: L/D in Different Wind Speed for each angle of attack 3.4: Twist Distribution 3.4.1 Computation Using equations 10, 11, 12, 13 and 15 N=450RPM r1 

30  0 .1 300

U= 4.5m/s (wind speed) U= 6° 30

N

2r  450   2  .360  60  60 

  16 .964 m / s



 16.964   3.769 U 4 .5

r   30   r .i    i   3.769   0.3769  300  R i 

 1 2 tan 1  3   r ,i

 2   tan 1  1   46.23  3  0.3769  

10   i    46.23 o  6 o  40.23 o 3.4.2: Computation Design Result

Fig. 3.3: Blade sectioning (ith radius)

ri 0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30 0.33

ri/R 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.2

 3.768 3.768 3.768 3.768 3.768 3.768 3.768 3.768 3.768 3.768 3.768

r,i 0.3768 0.7536 1.1304 1.8072 1.884 2.2608 2.6376 3.0144 3.3912 3.768 4.5216

Ɵ,i 46.23 25.33 27.66 22.37 18.63 15.9 13.84 12.23 10.95 9.9 8.31

Table 3.2: Complete Computation

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 6 6 6 6 6 6 6 6 6 6 6

 40.23 29.33 21.66 16.37 12.63 9.9 7.84 6.23 4.95 3.9 2.31

3.4.3: Preliminary Design

Fig 3.4.: Tip angle

and root angle 40.23o

3.4.4: Blade Specification

Fig.3.5: Modified Twisted Blade

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Fig.3.6: front view

Fig.3.7: back view

3.5 Construction Ultra-maker 3d printer in FABLAB Mindanao was used for fabricating the blades. The whole duration of printing a single blade takes about 7 hours to finish. The blade was originally designed to have a blade length of 300mm, but then due to some restrictions from the 3D-printer it was scaled down to 295mm. The fabricated blades were then attached to the turbine rotor which is also designed to be detachable for an easy shifting of pitch angles. It was then set-up in the wind tunnel at SPC Machine Shop. Gathering of results was made possible through the use of 2 industrial fans as a source of wind.

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3.5.6 Actual set-up

Fig.3.8: Wind speed measurement

Fig.3.9: RPM measurement using the tachometer

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3.6 Schematic flow of the system

Source of Wind

Wind Turbine in Wind tunnel

Power output

3.7 Data analysis The blade testing is held at St. Peter’s College Machine shop during the time where external wind condition is normal to avoid additional external force while the testing is on-going, also

the number of people were limited. The

blades were attached 1.42 meters away from the industrial fan. The test started by adjusting the pitch angle of the blade which is already attached to the turbine, after this set-up, the industrial fan is turned on. By the use of tachometer, RPM is measured at 5 different speed. Using the 5 different speed, the voltage, current, energy and power output were then read and collected. Gathered results from the testing were put in Chapter IV.

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