WIND TURBINE
Time Period: October 2016 - December 2016
Course: Three-Dimensional Modeling for Design
Skills Developed: Design thinking, Aerodynamics, 3D Printing
Software Used: SolidWorks
Project Background
The project aims to address the renewed interest in producing energy through a pollution-free mean of generating electricity. Often times this objective is accomplished through a system known as the wind turbine which converts wind energy to electricity. There are four major activities that compose the project: designing and creating the turbine rotor blades, the support tower and generator housing, determining the power output, and determining the stiffness of the wind turbine.
By designing unorthodox blades for this project, we aim to test how well our sickle-shaped blades will function when compared t o the conventional blades for horizontal-axis wind turbines. Furthermore, by incorporating both cylindrical and conical shape into our tower, we hoped to increase our stiffness-to-weight- ratio in order to allow our tower to withhold strong currents of wind.
After the designing and production stages of our project the final height of our tower turned out to be 16 inches tall and it weighed 370.5 grams, excluding the weight of the motor, and the cost of production was $121.50. We, then proceeded to test our tower by placing our wind turbine 14.5 inches away from the fan to apply wind that came into contact with the blades at 25.2 miles per hour. By testing our wind turbine multiple times with varying the load on the motor, we discovered that our wind turbine has a max efficiency percentage of 82.2% and achieved a stiffness constant of 1361.61 kg/mm. Overall, the aforementioned data show that we were able to successfully design a sturdy, working wind turbine that produces electricity. Although we had slight misunderstanding of the requirements we had to address, we were able to fix that issue by sanding down parts of our tower and inserting a housing for the motor. Overall, we were able to achieve our overall goal of producing a functioning wind turbine that convert wind energy to electricity.
DESIGN
Using a basic understanding of aerodynamics and 3D printing, we began to design the turbine as a team. This process also involved analyzing the mass properties as our task was to minimize weight of the unit.
The profile of each blade is a scaled down version of the prior profile as it extends farther from the hub. The angle of attack decreases and increases. The goal of our blade was to maximize surface area while minimizing wind resistance. The blade is extremely thin. The fillet is 0.008in which is about 0.20cm, the minimum layer height for most Fused Deposition Modeling 3D printers.
The idea for the tower is to have a series of extruded circles (the shape that encases the most area given a perimeter) to make the tower as wide as possible with limited 3D-printing filament. The longest cylinder tapers off to a conical shape to distribute stress into the base.The shell of most of the tower is 0.18 in, but the base rim (see CAD files section) is 0.20 in to add extra stability. The motor encasing is also a 0.18 shell that form fits a motor and has the motor rest on top.
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BUILD
We prototyped the blades printing them on a Monoprice Makerselect V2 FDM printer with PETG 3D FDM (1.75 mm) filament and PLA 3D FDM (1.75 mm) filament. All the support was removed with a precision knife, and sanded for smoothness.
Later, the blades were printed with the tower using ABS. The tower was printed in two pieces. These two pieces were glued together and onto the plate with Loctite instant adhesive 495. Parts that did not fit perfectly were filed down with various grit fils and sanded down with sandpaper.
TESTING
We ran two tests on this model: power generation and stiffness.
The purpose of testing the power generated was to find the wind turbine’s maximum power and under what load this occurred. In order to test for power, we needed to find the voltage and current. We used a power meter which was connected to the motor and to the load box to read the output voltage, current, and power values. We used a load box which contains a potentiometer and several LEDs to increase resistance, thus drawing more power from the turbine. In order to obtain the desired wind speed of 25 mph, we used a wind speed measuring meter to adjust the speed and location of our turbine until we reached the desired wind speed. We used a tachometer to measure the speed of the rotor.
The purpose of testing stiffness is to see how much stress the tower can withstand compared to its volume. The deflection of the tower is measured by loading the top plate (where the motor lies) with weights connected to a pulley with a string. These weights acted as an applied load. We also used an eyebolt which was attached to the upper plate of our turbine. This was attached to a string pulled over the pulley with the load hanging on it. Finally, we used a dial indicator to measure the displacement of the top of the tower with each added load.
TESTING OUTCOMES
Based on the test results, we made many observations:
The voltage decreases as current increases.
As the current increases, the power generated increases. However, once the current reaches a certain value, the power generated has reached its peak and begins to decrease as the current continues to increase. In the case of our turbine the power generated increased until the current was 1.16 A with 0.1261 mW of power and decreased as the current kept increasing.
The displacement of the turbine increases as the load increases. This is due to the offset of the center of mass as more weight is added. Our data appears to be almost perfectly linear with a correlation factor of 0.999. Our turbine was very strong and is able to withstand heavy loads having produced a high stiffness value of 1361.61 kg/mm.
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Max. Power: P = 0.1261 mW when I = 1.16 A
For this particular wind turbine the theoretical power generated is 0.1533 W
The peak efficiency of this turbine is 83%
Conclusion
With the 3D designs we drafted and printed, we were able to successfully construct a working wind turbine that generated electricity. Rather than designing conventional blades, we decided to try an unorthodox blades for our wind turbine, creating sickle-shaped blades. As for the tower, we believed circular shaped cross-sections would allow us to build a stiff tower. Thus, we decided to use a mixture of cylinder and cone to create a tower that could withstand heavy winds. We were able to create a turbine with an 82.2% efficiency if 100% efficiency represents the theoretical power generated by our tower.
According to the American Wind Energy Association, conventional wind turbines’ capacity factors can vary between 40 percent and 80 percent. Although we did not have enough data points to calculate our wind turbine’s capacity factor, our wind turbine generated 82.2% of its theoretical maximum power output. While it may seem like our peak efficiency may sound like we have invented a revolutionary wind turbine, that certainly is not the case. Developers often have to consider other factors of constructing wind turbines, such as the cost of producing such wind turbine, as well as which environment the wind turbine will be placed in. With all of these factors on mind, developers design wind turbines that vary in capacity factors to create best design for the given environment and funds. Therefore, I cannot say that we created the best wind turbine, but we designed a functioning wind turbine.
REFLECTION
Through this project, I was able to solidify my familiarity with Solidworks and familiarize myself with wind turbines. I learned about how wind turbines worked along with the theories behind wind turbines through this project. Furthermore, I learned how to calculate and analyze efficiency of wind turbines. Although our wind turbine worked, I believe we could have done better if we had a better understanding of aerodynamics for our blades thus designing better blades that could generate more electricity for the given volume limit. Furthermore, I believe had we made the tower a truss structure, it would have improved our stiffness to volume ratio.