Wind Diverting Integrated Generator Turbine

Horizontal axis wind turbine was the obvious choice for this project. HAWTs produce the most power from a given volumetric flow rate of a fluid and they are more durable while experiencing the most axial forces. At high speeds, HAWTs can experience high turbulence effects with the addition of a horizontal shaft along the axis of the turbine to allow for the turbine to turn the generator and produce power. To minimize and neglect these effects, the turbine was designed with the intention of integrating the generator on the outer perimeter of the turbine. The turbine blade design is illustrated below.

The blades were designed as airfoils to allow for the maximum amount of lift drag on them for use vehicular conditions. The airfoil and its characteristics used in the design is illustrated below.

This clockwise-turning turbine will be the only object in the path the fluid flow will encounter. Typically, the generator sits behind the turbine blades along with the shaft, incurring turbulent flow effects and drag forces that will now be minimized, or even eliminated. For power generation, the generator used in this design will use a coil and magnet configuration that uses the principle that a moving magnetic field through stationary coil cross-sectional areas produces a voltage. This voltage produced, V, is related to the strength of the magnetic field produced by the magnet, B, the number of turns in each coil, N, and the cross-sectional area of a given coil, A, through the following equation:

This allows for the design of both the yoke and the stator. The yoke, illustrated below, is simply a cast iron U-channel used to hold the magnets and amplify the magnetic field produced by the magnets.

The stator was designed to be mounted on the actual casing of the turbine and sit within the U-channel to allow for the penetration of the magnetic field through the cross-sectional area of the coils. The stator is illustrated below.

Lastly, the casing of the entire turbine was designed to divert air in a way that would reduce forces on the vehicle this would be mounted on. A straight cylinder to house the turbine would cause for the air at the outlet of the turbine to encounter the vehicle parallel to its direction of motion. To reduce this, the housing was designed to be in a “Y” shape to divert the air at a 15 degree angle to minimize the component parallel to the direction of motion. This diversion was also crafted to be as smooth as possible to reduce the radial force effects of flow redirection. The casing and assembly are illustrated below.

Limitations of Manufacturing - Efficiency Losses

Due to the constraints of time and manufacturing costs, the design had to be altered for proof of concept. One of the defining characteristics of this design, the “Y” shaped housing had to be changed to a straight cylinder to prove the concept. Manufacturing a housing that would have the appropriate curve to minimize the effects of the forces applied to the vehicle by the air at the outlet would not only be very expensive. This is going to yield higher forces experienced than anticipated. Additionally, manufacturing a turbine that has airfoil blades would be extremely expensive and difficult to manufacture at such an elementary stage. Therefore the turbine blades had to be 3D printed through a multilayer extrusion process. This does not produce the smooth contours an airfoil needs to perform at its best. Ridges are left behind through this process that create a rough surface and will also lead to a decrease in efficiency. Lastly, the stator would also be an expensive and difficult piece to manufacture. Ideally, the stator would be manufactured out of cast iron as well to, again, amplify the magnetic field and maximize the induced emf in the coils. Because machining a part like this is costly, it was also 3D printed using the same extrusion process as the turbine blades.

These all lead to a less than ideal situation for the manufacturing of the wind diverting integrated turbine generator prototype. However, under the conditions the prototype was produced, the turbine can still be deemed feasible.

Final Prototype

The final prototype is shown below. The final form factor of the prototype had to be altered for manufacturing reasons discussed in the ‘Limitations of Manufacturing’ section above.

Time constraints and issues with 3D printing tolerances led to the omission of the yoke, which is used to amplify the magnetic field, and the inclusion of bearings. Bearings were included in the design, but required the presence of the yoke for them to be used.

Results

After completing the prototype, tests were run for the proof of concept. The aim was to prove that a turbine in this integrated generator configuration would be able to produce any power. The prototype was tested on a car with a speed of approximately 60 mph. In this testing configuration, the integrated generator turbine prototype produced 1mW of power. This small, almost worthy of disregard, power output was expected for several reasons. First, the materials used in the construction of the generator were not ideal for the production of power. As stated before, an iron stator would greatly increase the power produced. Second, the yoke was not included. A yoke would be able to amplify the magnetic field by the order of a thousand. Third, the rotation of the turbine was stifled greatly by the omission of the bearings. Rather than rotating on ball bearings, the plastic turbine had to rub on the rough plastic casing that produces high friction forces, especially when encountering 60 mph winds. Lastly, the turbine did not sit well in its casing. The turbine tended to vibrate as it spun and did not experience a smooth rotation. All these factors lead to a less than ideal design and to the small power production measured.

** Theoretical force calculations can be found in the appendix section.