The objective of this project is to design and build a vertical-axis wind turbine to generate electric power. The vertical turbine has the advantage of being deployable in urban or other crowded zones, whereas horizontal-axis turbines require a large footprint due to the space needed for safe spinning of the blades. Further, a vertical axis turbine does not need to be facing any particular wind direction, which is important in a region where wind direction changes day to day.
Component Selection and Design
Readily available materials were selected for the turbine in order to avoid the purchase of new materials, as this fit with the eco-friendly theme of our design.
Table SEQ Table \* ARABIC 1: Parts List for final design.
The sheet aluminum blades, ball bearings, steel dowel, DC motor, and all wooden components were reclaimed from scrap sources; the pulley components and fasteners were bought new and/or machined from raw materials.
Two ball bearings were deemed sufficient for smooth operation of the shaft as the axial loads were found negligible. The blades and flaps were cut from sheet aluminum, and manually into the required geometry as needed; the sheet aluminum offers sufficient stiffness with minimal volume and weight, minimizing the torque losses when starting the turbine from rest.
Initially, the curved blades were mounted to the shaft flush, but upon testing it were found that placing spacers between the blades and the shaft greatly increased the speed of the turbine due to Bernoulliís principle. Testing with this spacer configuration on a moving ATV yielded smooth operation even at high wind speeds
A multi-radius pulley system was made using aluminum and brass for their relatively high density. These act to reduce the high speed of the turbine, and also to increase the moment of inertia of both the turbine and motor for smoother operation. A permanent magnet DC motor was chosen for its simplicity and ability to generate power at a variety of speeds.
The flaps were found to make the speed intermittent at low speeds, and then stopped generating any torque at high speed. At high enough speed, the flaps did not have enough time to drop down from their horizontal position at each revolution, and so would stay horizontal, and so the flaps were eliminated from the final design. One of the motors used during testing did not generate the operating voltage, and shocked anyone touching the motor, so this motor was replaced with a similar one in the final design.
The final design, featured on the right, does not use the horizontal flaps, shown on the left. All other components of the design are implemented, and 1.5 V DC is generated by the motor during operation. The turbine runs at approximately 200 RPM in regular breeze, and higher when gusting, but the motor produces 1.5V once the speed reaches 100 RPM.
What we Learned?
During the design process, we learned about basic aerodynamics, and how a fast flow of air across a surface generates a force on the opposite side of that surface. We also learned how a permanent magnet DC motor has the advantage of simplicity, only two wires, and compact size. Most importantly, the advantage of reusing readily available materials was learned, as the cost of the final design was minimal.
The mechanical portion of the wind turbine functioned as needed after some redesign, operating at consistent and high speed in a variety of winds in field tests; using a ready-made PM DC motor made it easy to generate a voltage from this rotation, however this voltage is small. Future amendments to the design could include multiple flaps, different blade geometry, as well as a motor better able to convert the high RPM of the turbine into a high voltage. A redesign could use a variable transmission coupled to a synchronous motor in order to generate usable AC power for domestic use or as a supply to the local grid.