Wind Turbine Model for Wind- Tunnel Testing - The City College of ...

City College of New YorkSpring 2012 Senior Design Project: ME 473Wind Turbine Model for Wind-Tunnel TestingInstructor: Professor WatkinsAdvisor: Professor AndreopoulosDesign Team:Christopher Ruano (Leader)Kam CoinLuis Roldan1

Table of ContentsNomenclature3Introduction4Problem Statement 5Product Design Specifications 5Product Architecture 5Design Concept7Turbine Geometry 7Airfoil Selection 8BEM Theory 10Linearization 12Alignment 13Final Design 15Analysis 16Parametric Design19Motor Selection 19Nacelle Design 202

Tower Design 21Base/Support 22Final Assembly 23Design Embodiment24Wind Turbine 24Manufacturing and Fabrication 26Assembly 29Performance Evaluation31Mass Properties 31Experiment 1 Turbine Configuration 32Experiment 2 36Experiment 3 38Experiment 4 41Conclusion and43RecommendationsAcknowledgements463

NomenclatureAngle of AttackPitch AngleTwist AngleDensity of airTip speed ratioTurbine time constantRelative angleAngular VelocityNumber of BladesChord lengthPower CoefficientLift CoefficientDrag CoefficientTurbine diameterCurrentTurbine radiusEffective blade radiusMechanical PowerElectrical PowerVoltageCenter of gravityCenter of pressure4

IntroductionWind turbines are quickly becoming the world’s fastest growing renewableenergy technology. Over the years, wind turbines have become reliable, efficient andreduce cost of energy. Wind turbines have the ability to power homeowners, farms andeven business owners. Wind turbines are often used in arrays known was wind farms.These wind farms can be seen throughout the world and are gaining popularity here inthe United States. Wind turbine farms placed on the land are called Inland Wind Farmsand turbine farms placed in the sea are called Offshore Wind Farms. This senior designproject will model both an Inland and Offshore wind farm. Before the wind farm can becreated, a single wind turbine must be designed.The wind turbine is assembled in four parts as shown in figure 1. The first part isthe three blade wind turbine design, which converts the kinetic energy of the wind intoMechanical energy. The wind turbine is then connected to a Nacelle, the housing, whichconceals all mechanical components like the motor, resistor and wires. The third partsupports the wind turbine and nacelle to a certain height above the surface. And lastly isthe support base. This will support the entire wind turbine assembly and connects it tothe foundation.Figure 1 Wind Turbine Assembly5

Problem Statement and ObjectiveThe purpose of this project is to design a scale down version of a wind turbine.Along with the wind turbine, a wind farm will be design in the process. The goal ofdesigning the wind turbine is to be able to plot power as a function of wind velocity. Ourobjective is to collect data on the behavior of the wind turbine. Some of these datainvolve finding the rotation speed at a given wind velocity. The power that the windturbine generates will be calculated.Product Design SpecificationThe wind turbine design has to be a scale model three-blade horizontal axis windturbine. The model needs to fit a 4x4x24 feet working section of the department windtunnel. The wind turbine needs to be rugged to withstand high wind speeds as well asversatile to allow interchangeability.Project ArchitectureThe wind turbine with be tested from inside the department wind tunnel. Asshown below (Figure 2). From the schematic diagram the wind turbine will be stationedin inside the wind tunnel. The wind tunnel will provide different wind speed variation.The wind will cause the turbine to rotate by aerodynamic forces. A high speed camerawill be used to calculate rotation speed, which in this case will act as a tachometer.Since the wind turbine is connected to a motor which outputs voltage, the powergenerated will be calculated from the voltage. This data will be collected through a dataacquisition system. For this project a data acquisition system was not available, sosimple multimeters were used to record the data.6

Figure 2: schematic diagram of wind turbine.7

Design ConceptTurbine GeometryWind turbines are characterized by their diameters. The diameter of a windturbine s defined by the diameter of the imaginary circle made around the turbine.Figure illustrates how the diameter of the wind turbine is measured. The radius of theturbine is then defined as the distance from the hub to one of the tips of the wind turbineblades. The blade itself can be broken into several subsections such as the shaft andeffective blade. The effective blade is the part that is responsible for creating theaerodynamic forces that produce the torque. This section is formed several airfoils, andresembles that of a delta wing. Most of the design of the wind turbine will focus on thedesign of the effective blade.Figure 3: Wind Turbine GeometryThe blade can be divided into small elements, dr, that consists of airfoils. Eachblade section has a relative angle, or the angle facing the relative velocity while rotating.The difference between the relative angle at the tip and the relative angle at the root isknown as the twist angle, or the amount of twist on the blade. Figure 4 shows the layoutof a blade section as seen from the right. This figure illustrates how a portion of the8

we could compare different airfoils within the series. From analyzing the design ofcurrent wind turbines, and researching their construction, we noticed that the airfoils arefairly thin and significantly curved. We then looked at which NACA profiles matched thisparticular shape. Determining this compatibility was fairly easy because the NACAprofiles have a very particular classification. The four digit series consist of four digitnumbers that describe the curve, or camber, of the airfoil, the placement of maximumthickness from the leading edge, and the maximum thickness as a percentage of chordlength. For example, a NACA 2412 has a camber value of 2, has a maximum thicknesslocated 4/C, and a thickness of 12/C.The airfoil that was selected had to have a high camber, and overall thin shape,but also had to have more of a thickness towards the root of the blade. The initial designwas composed of a NACA 2412 airfoil at the root and NACA 6410 airfoil from mid to tip,but this blade was too thin at some points, and would not lend itself to 3D printing. Itwas also more difficult to align the airfoil sections since they had different center ofpressures. One modification that had to be made was to choose an airfoil with a thickersection. For the final design the NACA 6412 was chosen, but it was also modifiedslightly so that it was slightly thicker than the NACA 6412. The figure below shows acomparison between the modified and unmodified NACA 6412 airfoils.0.4NACA 6412NACA 6412 Mod0.30.20.10-0.1-0.2-0.30 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Figure 5: NACA Profile10

Blade Element and Momentum TheoryAfter the airfoils that would constitute the blades of the wind turbine wereselected, determining the chord lengths and angles of the airfoils then had to bedetermined. These parameters depended upon how fast the wind turbine was going torotate and how much power was going to be generated with respect to wind velocity.From the previous section these parameters were derived from the tip speed ratio andthe power coefficient of the turbine, respectively. There are several methods commonlyoutlined by sources on wind turbines. Perhaps the most common is known as BladeElement and Momentum theory, or BEM. BEM theory divides the blade into severalsmall sections and determines the chord length and relative angle at these sections.This is done by applying the momentum equation and solving for the torque generatedat each section of the blade. These equations are outlined below.The first step in defining the blade shape is to break up the blade into severalsmall sections. From the figure below, we see that the blade section, r, starts at the root,so r=0, and the at the blade tip r=R. The tip speed ratio is then defined for eachindividual section of the blade. Since we know the tip speed ratio, and the coefficient oflift for the individual sections of the blade, we can then solve for the relative angle ateach individual section. The tip speed ratio for each of the blade sections is thendefined. The chord length that is necessary to produce the lift force is calculated by thesecond equation.11

c/RPitch AngleThe pitch and twist angles are then calculated by subtracting the angle of attackfrom the relative angle. We can then plot how the chord length and pitch angle changewith blade section r. In order to make this more applicable to any length of the blade,the parameters are normalized by the total length of the blade, R. The plots for theseparameters are provided below. The resulting chord lengths and pitch angles are tooexaggerated for implementation on modern wind turbine designs. This is because BEMtheory should only be used as a starting point for design, further refinement of the bladeshape is necessary for the final design. It is often recommended that a linearization ofthe chord length and pitch angle be made so that the blade becomes sleeker and easierto manufacture. If we were to construct the blade using specifications, the blade wouldalso look awkward and un-aesthetically pleasing. The only way of verifying whether ornot the final design of the wind turbine matches up with the design parameters is tophysically test them using wind tunnel tests, or to run computational fluid dynamicstudies using finite element software.0.50.40.30.20.10-0.16050403020100-0.20.2 0.4 0.6 0.8 1r/R-100 0.2 0.4 0.6 0.8 1r/R12

LinearizationLinearization of the blade involves describing the chord length and pitch angle forthe sections throughout the blade with linear equations. These equations are formulatedby picking two points relatively close to those found by BEM theory and drawing astraight line between them. This line can then be described by a linear equation usingthe points before. The reason for linearizing the chord and pitch distribution is becauseit makes the turbine more aesthetic. Most large scale wind turbines do not have theshape found from BEM theory. Another reason is that the linearized blade is easier tomodel and manufacture. The linearized chord distribution throughout the chord is shownin figure 6. The equation used for the chord distribution is shown under the figure. Thepoints chosen are labeled a and b. The point a is at the start of the effective blade, andb is at the tip. It is evident that the chord length decreases throughout the blade so a isgreater than b. Similarly, angle e is at the effective blade and f is at the tip. We can seethe pitch angle decreases, so the blade twists up along the blade.Figure 6: Blade Linearization13

A MATLAB code was written to create a table of the blade sections, the chordlengths, pitch angles, center of pressure, and centers of gravity. This MATLAB code isentitled Turbine Design, and is available in the group project website or dropbox. Theinputs for the code are the linearizations a, b, e, f, and the length of the blade. The tableis created by using the chord and pitch angle distribution equations above. The tablealso features the center of pressures and centers of gravity for each of the bladesections. The methods used to determine this are described in the next section, and areprimarily used for alignment of the blade sections. The output for the code is a text fileof the table created. This text file can then be read by another code used to create andalign the sections.AlignmentDetermining this location along the airfoil is well documented since it is used asthe location for applying the aerodynamic forces. The center of pressure is defined asone quarter of the chord length minus the pitching moment at one fourth of the leadingedge divided by the lift force. Since we don’t know the pitching moment or the lift force,we can determine the coefficient of moment and coefficient of lift for the airfoil used atthe angle of attack selected. The equation for the location of the center of pressure thenbecomes the second equation below.The center of gravity for each of the individual airfoil was also calculated by usingthe built in Evaluate feature in SolidWorks. This feature displaces the x, y, and z pointsfor the center of gravity. We then tabulated the results for the center of pressure andcenter of gravity for each of the airfoils shapes. The airfoils were then aligned in their x-position by their center of pressure, and y-position by their center of gravity. The airfoilsare then rotated about the location of alignment. The amount that they are rotated isdefined by the pitch angle calculated in the previous section.14

A separate MATLAB code was written to create the airfoil shapes and align themaccording to the method described above. This MATLAB code is called airfoils becauseit creates the exact airfoils that will be used for the solid model of the turbine. The codeinputs the text file from the code used to design the blade. It begins by creating theairfoil shapes with the exact chord lengths determined by the design process. Theairfoils are then aligned in the x-axis by their centers of pressure. This becomes theorigin of the blade. Each blade profile is then tilted by the pitch angle and then all theprofiles are shifted to the center of gravity of the first airfoil. This is where the effectiveblade will be connected to the rest of the turbine blade and hub. A separate text file iscreated for each airfoil. The text file has the x, y, and z coordinates of the airfoil. Thesetext files can then be directly imported into SolidWorks, where the actual blade iscreated.3210-1-2-3-4-5-5 -4 -3 -2 -1 0 1 2 3 4 5Final DesignFigure 7: MATLAB ProfilesThe solid model of the wind turbine begins by creating the blade sections inSolidWorks. This step was made simpler with the text files created by the MATLABcode used before. The text files are imported by the use of the insert curve through xyzoption. The shaft of the blade is made after all the sections are imported. The hub is15

AnalysisOnce the turbine has been designed using SolidWorks, the analysis of theturbine can begin. CFD simulations are performed on the finished wind turbine design todetermine the performance of the turbine. The setup for the simulations is a singleturbine placed inside a control volume or enclosure, and inputting a wind velocity in thedirection of the turbine. After the geometry is created, a mesh is formed around theentire geometry. The boundary conditions for the simulations are the inlet velocities thatwere similar to those used in the wind tunnel. The simulations are done using a nonrotatingturbine. A user defined function, or UDF, was developed by graduate studentsthat rotated the turbine according to torque developed on the turbine and the moment ofinertia. The code assumed a steady state angular velocity according to the last timestep of the simulation, and so the rotational speed was somewhat arbitrary. Theequation that describes the angular velocity of the turbine with respect to time is morecomplicated, and so this is only determined by the use of actual experiments conductedon a physical model.Figure 10: Fluent MeshThe simulations only calculate the velocities and pressures throughout theturbine when it is not rotating. The forces and moments can then be calculated by17

Fluent according the pressures developed on the turbine. These types of reportscalculate the pressure per each face of the mesh, and so can used accurately todetermine the torque of the turbine. This is accomplished by telling Fluent in what originand what axis to calculate the moment developed, and since the turbine rotates about acertain axis, the torque is this moment calculated. An example report is shown in thefigure below. The highlighted section is the torque that was calculated. The torques arethen tabulated for each of the velocities used and plotted. A plot of the torques witheach of the velocities is shown in the figure below.Figure 11: Fluent ResultsFigure 12: Torque Report18

Torque (Nm)0.010.0090.0080.0070.0060.0050.0040.0030.0020.00102 3 4 5 6 7 8 9 10 11Wind Velocity (m/s)Figure 13: Fluent Calculations of Torque19

Parametric DesignMotor SelectionFor this project, the power generated by the turbine will be measured byelectrical means. This requires that the turbine be attached to some type of generator.Currently, there are no generators that are made to this scale, but small DC motors canbe used effectively as generators. The selection of the motor had to be critical becauseit must be around the same scale as the turbine, be efficient at the speeds of theturbine, and have a small starting torque. Of those requirements, the most importanthad to be the low starting torque. The starting torque is the torque necessary for themotor to start rotating. If this is too high, the turbine will not start to rotate at low windspeeds and so have a large cut in wind speed. The overall angular velocity will also beaffected because some of the torque produced will be consumed by the motor. Thismeans that the motor shaft had to spin easily when rotated.Figure 14: Pololu Brushed DC MotorThe selection of the motor analyzed several different types of motors fromdifferent manufactures, but ultimately one motor was chosen that most closely fit all therequirements. This motor is brushed DC motor from a company called Polou. The selleralso provided the efficiency of the motor along with some operating parameters. The20

adapter will make a tight fit with the tower so that movement of the two components isdifficult, but still possible if adjustment is necessary.Tower DesignThe tower holds the turbine at a certain height so that the turbine blades arecapable of capturing the most wind. The height of the tower is dependent on the velocityprofile of the environment. If for example the turbine is placed in an area that is heavilycondensed with trees and other obstacles, the velocity will be low towards the ground,so the tower should be built higher above the ground. If the turbine is placed in an areathat is relatively isolated, like the plains or ocean, the tower does not have to be as tall.The expense of the tower increases the taller it is, but the power extracted alsodramatically increases, so there is often an optimization of this length. Since the modelturbines in this project are supposed to model both land and offshore wind turbines, theheight is left to interpretation. On average, the tower height to turbine ratio is about oneto one for most turbines, most of the times it is a little over one. For this project thetower height to turbine diameter is 1.25, which would make the height 25 centimeters. Inthe solid model, the tower is design as a hollow tube. In this way, the wires can berouted from the motor to the base.Figure 16: Tower22

Base/SupportThe base is the part of the wind turbine assembly that supports the tower andprevents it from tipping over during high wind speeds. There was some concern that theturbine assembly would behave like a cantilever beam when subjected to high winds,but this could be avoided if the tower was sturdy and if the base supported theassembly sufficiently. At first, the base was designed as something that resembled aplumbing flange, but this designed left the wires from the motor hanging out andoccupied too much space. The redesigned space is a lot more space friendly andincorporates a method for connection to a data acquisition system. It is still sturdyenough to support the wind turbine assembly under high wind speeds and has amethod of attachment to some sort of platform via small holes around the perimeter.Figure 17: Base DesignMost data acquisitions use BNC connections to transmit the analog signal fromsensors to the analog to digital converter inside. In this situation, the generator acts likea sensor that transmits the amount of voltage being produced. It could be said thatthese BNC connections are an industry standard method of connection. There alsoplenty of BNC cables located in the departmental wind tunnel room. A male adaptor isconnected to the base so that a BNC cable with a female end can be attached. Theseadaptors are available from most electronic parts retailers. A picture of BNC adaptorthat was used is shown below.23

Figure 18: BNC PlugFinal AssemblyThe final design of the wind turbine is the wind turbine assembly. The entire windturbine assembly consists of all the components mentioned above. The wind turbine isplaced onto the motor via a small hole in the center of the turbine. The turbine is held inplace by a tight fit made between the two components. The motor is placed into thenacelle, and is held in place by the plastic standoffs. The nacelle is assembled withmachine screws. The nacelle and wind turbine are attached by an adaptor that is gluedonto the bottom piece of the nacelle. The tower connects to the base again by tight fit,and the wires that connected to the motor are routed from the tower to the base. Theterminals are connected to a BNC connector, which is capable of attaching to most dataacquisition systems. The entire assembly can be bolted or screwed down to some sortof platform by the four holes around the base.Figure 19: Final Wind Turbine Assembly24

Design EmbodimentWind TurbineThere was a great amount of consideration taken into the design of the turbine,especially to the turbine blades. That is why it is important the turbine be manufacturedas closely as possible to the solid model. Using inadequate methods of manufacturingwould jeopardize the entire project since any data collected from the physical modelwould not reflect theoretical values. The method that was chosen to be most suitable forthe creation of the wind turbine was 3D printing. The first step to having a 3D printedmodel was to find a source for printing. The 3D printer in the school was deemedunsuitable as the resolution was fairly low, and the quality of the finished product wasrough. A company called Shapeways, which is located in Long Island City, printedmodels based on the stl file submitted. The solid model of the wind turbine wasconverted into an stl file, but before the file was uploaded it had to be refined so that thequality would be high.Figure 20: Shapeways ModelUploading a file that was acceptable by Shapeways and that was able to printwas somewhat of a challenge. This is because Shapeways has certain conditions for25

Figure 24: Tower ManufacturingAll of the nine bases were fabricated from two inch thick aluminum stocks thatmeasured eight by eight inches. The tool path was again made in HSM, but requiredmore complex operations since it would be 3D contouring. A picture of what the stocklooked like after it was milled is shown in figure . After the bases were milled out, theywere sanded to remove the tool marks and polished to give them a finished look. Theholes around the perimeter and the hole for the BNC connector were drilled using anordinary hand drill. This completed the fabrication process, and the task of puttingtogether all the parts came next.29

Figure 25: Base ManufacturingAssemblyOnce all the components of the wind turbine were manufactured and ready, theassembly of the components could be begin. Since multiple turbines had to be puttogether, all the turbines were assembled using an assembly line method. That meantthat one stage of the assembly was done at the same time for all the turbines, and allthe turbines were finished at the same time. This process began by gluing all the partsthat made up the nacelle. These included the plastic standoffs and the adaptor. Theadhesive of choice for this step was JB bond epoxy resin. The BNC connector was alsoglued onto the base because threads were not able to be made. The connections forthe connector were soldered, and the tower was placed inside the base.Figure 26: Assembly Method30

The tower was connected to the nacelle by means of tight fit on to the adaptor.Before the motor was placed inside the nacelle, the wires and a resistor were solderedonto it. The resistor made it easy to measure the voltage and the current. Once Themotor was fitted onto the nacelle, and all the wires were properly placed, the two nacellepieces were joined together. The circuit was then checked to see if there were anyshorts by checking the voltage when the motor was spun. The wind turbines were thenplaced onto the motor shafts. A very tight fit was necessary so that the turbines wouldnot slip during high wind speeds. The turbines were then ready to be used inside thewind tunnel.Figure 27: Wind Turbine Farm31

Performance EvaluationMass PropertiesThe theoretical calculations of the wind turbine depended on several massproperties of the wind turbine. This included the total mass and the mass moment ofinertia. SolidWorks has an accurate calculator for the mass properties, but this requiredthat the material type be chosen. The material for the wind turbine was nylon, but thedensity of nylon could not be used because the wind turbine was 3D printed, and so nota homogenous material. To determine the density of the turbine, we got the mass froma scale and divided by the volume determined by SolidWorks. The density came out tobe 920 kg/m^3. This was close to the density of nylon, which is about 1200 kg/m^3, butthe turbine is not completely solid. Once the density was determined, the density wasinputted into the solid model, and the mass properties were evaluated.Figure 28: Mass Determination32

Experiment 1The purpose of this project was to examine the behavior of wind turbines andmeasure the power of the turbines for given wind speeds. Before several wind turbinescould be placed inside the wind tunnel, each turbine that was to be used had to beplaced inside the wind tunnel alone. This way, the angular velocity of the turbine can bemeasured at each wind speed. This would also serve in calibrating each turbine. Eachturbine had to be calibrated because the motor of each could differ slightly. Theexperiment began by placing the wind turbines inside the wind tunnel and the windspeed is set according the frequency control. Once the wind enters the wind tunnel, theturbines begin to spin, and a voltage and current is measured by the multimeter. Theelectrical power generated is then calculated by the equation shown below. The angularvelocity is captured by the high speed camera. A small mark is made on one of theblades of the turbine, and the number of frames per rotation is counted. The power andthe angular velocity are plotted against the wind speed.Figure 29: Wind Turbine Calibration33

Angular Velocity (rad/s)Electrical Power (Watts)The plot of angular velocity versus wind speed for the first, second, and thirdturbines are shown in figures 30, 31, and 32, respectively. The angular velocity for theturbines are calibrated by the voltage produced. The mechanical power for the turbinesis then calculated by multiplying the torque times the angular velocity. The powercoefficient and tip speed ratio can then be derived for each of the turbines. Theelectrical power for the wind turbine is calculated by the product of the voltage and thefrequency measured. The electrical power for each of the turbines is then calibrated byeach of the voltages. We can see that all the turbines rotate at the same speeds, buthave some differences in the electrical power. This is because of the differences of themotor.200Motor Calibration for Turbine 10.010.009Motor Calibration for Turbine 1180160140120100800.0080.0070.0060.0050.004600.003400.002200.00100 0.1 0.2 0.3 0.4 0.5 0.6 0.7Voltage (V)00 0.1 0.2 0.3 0.4 0.5 0.6 0.7Voltage (V)Figure 30: Calibration for Turbine 134

Angular Velocity (rad/s)Angular Velocity (rad/s)Electrical Power (Watts)Electrical Power (Watts)200Motor Calibration for Turbine 20.01Motor Calibration for Turbine 21800.0091600.0081400.0071201008060402000 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Voltage (V)0.0060.0050.0040.0030.0020.00100 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Voltage (V)Figure 31: Calibration for Turbine 2200Motor Calibration for Turbine 30.01Motor Calibration for Turbine 31800.0091600.0081400.0071201008060402000 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Voltage (V)0.0060.0050.0040.0030.0020.00100 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Voltage (V)Figure 32: Calibration for Turbine 335

Figure 33: Turbine 1 Power CurveFigure 34: Turbine 2 Power Curve36

Figure 35: Turbine 3 Power CurveExperiment 2The second experiment consisted of 2 turbines positioned side by side. The twoturbines were placed equal distance off the wind tunnel wall. The purpose of setting theturbines in this manner was to see the effect of the turbines when they are placed sideby side. The turbines are both calibrated. We were aware of the fact that these twoturbines were not exactly equal distance. There was some inaccuracy. The two turbinesthat were calibrated were also off by 2-4%. This is due to the manufacturinginconsistency of the motors. The distance between the two turbines was 3D. 3D is thestandard length of most offshore wind farm. The diameters of the turbines are 20cm.The figure below shows the visual illustration of the setup. (figure 36)37

Figure 36: Two Wind TurbinesThe experimental result did not show any change in the power of these twoturbines. As mention earlier, we have to take into account that the difference in thecalibration and the inaccuracy when setting up the turbine, equal distance from the wall.The both of the turbines were set to be 1 foot away from the wall, but we mounted theturbines on plywood. The plywood was not all the same size.Taking account of the discrepancies, the power output did not change. We hadsimilar results from both of the wind turbines. This is the last analysis we will be doingside by side. The change in power is insignificant. They both remain the same We cancome to a conclusion wind turbines placed at 3D side to side will not have any drop inpressure. We can see the Results shown below.38

Electrical Power (W)0.0120.01Side by SideLeftRight0.0080.0060.0040.00201 2 3 4 5 6 7 8 9 10 11Wind Speed (m/s)Figure 37: Side by Side ResultExperiment 3For this following experiment, 3 turbines (which was calibrated) were placedstraight behind one another. The distance behind one another was 6D (the conventionaldistance for offshore turbines). One of the major discrepancies in this experiment wasthe first turbine. The first calibration of the first turbine was 15% greater than the othertwo. We also have to consider the boundary layer effects. The first one was placedclose to the inlet. The experiment was continued to see the difference in angularvelocity. The figure below shows the setup of the experiment. (Figure 38)39

Experiment 4For the fourth experiment, we placed the turbines staggered to one another inrows. For this experiment, we moved the second turbine 1.5D to the left from where itwas positioned from experiment 3. From the 1 st experiment, we knew the first turbinehad some discrepancies, so we were expecting a similar result for this experiment aswell.Figure 40: Three Turbines StaggeringFrom the fourth experiment, we saw another significant drop on the first turbine.What we saw this time was a greater increase in the third row in power. The staggeringhelp overcome the wake distribution. The angular velocity also increased compared tothe 3 rd experiment. The gap between the 2 nd and third turbine in the power graphdecreased.41

Electrical Power (W)0.0120.01Coloumns StaggeringFrontMiddleLast0.0080.0060.0040.00201 2 3 4 5 6 7 8 9 10 11Wind Speed (m/s)Figure 41: Columns Staggering ResultsExperiment 5For this experiment, we positioned the turbines in corresponding distance. Wepositioned the turbines back to back. There was no staggering in this experiment. Wewant to see the effects the second turbine will have by placing the turbines in differentdistances. We placed them in a distance 1.5D, 3D, 4D and 5D from each other. Thistime the turbines were calibrated at the same amount. The difference was less than 2%.The turbines were also placed away from the inlet to avoid any boundary layer affects.We also saw the wake distribution with a smoke test. The setup is illustrated below.42

Electrical Power (W)Figure 42: Two Turbines 1.5DThis time the results were as expected. As we increase the distance, the powerof the second turbine increases. The slow motion video also shows the wakedistribution of the first turbine affecting the flow of the second turbine.0.010.0090.0080.007Back Turbine1.5D3D4D5D0.0060.0050.0040.0030.0020.00101 2 3 4 5 6 7 8 9 10 11Wind Speed (m/s)Figure 43: Results for the Back Turbine for Different Spacings43

ConclusionThe objective of the project was to increase the efficiency of the wind turbines inevery row after the first row. We were aware of the wake distribution from the slowmotion video. With a number of conducted experiments in the wind tunnel, we were ableto find the affects the turbines encounter and how to overcome them. The turbine’s thatwere designed were structurally stable to withstand high velocity in the wind tunnel.With the addition of the BNC connector, it was possible to measure the voltage withoutinterfering the wind flow. One important parameter of this experiment is the tip speedratio and the power coefficient. The turbine used for the experiment had the same tipspeed ratio and power coefficient. The tip speed ratio is the ratio between the rpm andthe wind velocity. All of the turbines had similar results. The power coefficient is theoutput of the electrical power over the input over the input power.In the Experiments, we took account of the boundary layer affects and theturbines design. We calibrated each turbines used. The calibration gave us angularvelocity as a function of voltage and power as a function of voltage. The use if the highsped camera helped us measure the RPM. The high-speed camera also shows thewake distribution. Experiment one was important in determining which turbines to use.We calibrated all the turbines. Experiment one also showed the wake distribution.Experiment 2 was to see any possible affect we may have in the power output byplacing the turbines side by side. We saw that there was affect. We concentrated ourexperiments on the affects we will have by placing the turbines in columns. For the thirdexperiment, we placed 3 turbines back to back. The distance between the turbines is6D. This experiment helps us acknowledge the boundary layer affects in the windtunnel. We saw the first turbine began to decrease in voltage, the second and thirdturbine showed predictable results. The third turbine decreased in voltage compared tothe second turbine. Later on in Experiment 4, when we stagger the turbines, we can seethe second and third turbines power outputs are similar. Staggering help us increase the44

efficiency of the turbines. The greater the distance of the turbines in row, the moreefficient each turbine will be. This was the purpose of the fifth experiments. By changingthe distance between the turbines, we see the power output increasing with greaterdistance.Staggering and increasing the distance between the rows will increase theefficiency. All the turbines can have similar power output if we can avoid positioning theturbines directly behind each other. We see this affect in the staggering experiment andthe fifth experiment.45

RecommendationsFor future studies, in order to have a complete wind tunnel, we should consider abigger wind tunnel. With a bigger wind tunnel, we can place more turbines and have amore in depth study. We should also consider a bigger wind turbine. With a bigger windturbine we will be able to see a greater wake distribution with the high-speed camera. Abigger turbine is also easier to manufacture. The motor used in this experiment is a dcmotor. We can optimize the wind turbine design with a magnetic induction motor. Thesemotors are generally used in actual wind turbines.The voltages were measured with a multimeter. One multimeter was needed tomeasure each turbine. A proper DAQ system with voltage display would make the setupof the project less stressful. The current DAQ does not display the voltage output. Thedata need to be exported to such program like matlab to find the average voltage. Thiswas time consuming.46

AcknowledgementProfessor WatkinsProfessor AndreopoulosProfessor GouschaMr. ChenLouis Hernandez47