| dc.description.abstract | As the wind energy market continues to expand, the need for a more diverse range of wind turbine technologies becomes increasingly apparent. Horizontal axis wind turbines (HAWT) have become the standard design for wind turbines over the past few decades and have been the go-to design used in wind farms both on land and off-shore. However, in residential and urban environments other types of turbine designs can help expand the reach of wind energy. Specifically, vertical axis wind turbines (VAWT) have shown potential for new applications of wind turbines in areas that are less suitable for typical HAWTs. The most common VAWT design is the Darrieus turbine, which use a series of straight, vertically oriented blades that rotate around an axis that is perpendicular to the incoming wind. However, this design has shown several disadvantages such as being unable to self-start and creating large amounts of noise. This project seeks to improve these characteristics by adding a helical twist to the blades of a Darrieus wind turbine and evaluating its benefits. With the addition of a helical twist, the gap between each blade begin to decrease as there is now a more fluid transition from one blade to the next as it rotates through the incoming wind. In VAWTs the blades chop through the incoming wind and in front of the center axis, which creates turbulence and causes a fluctuation in the torque produced by the center shaft. Adding a helical twist diminishes this “chopping” motion by allowing for a portion of the blades to nearly always be in front of the center axis. In order to evaluate the benefits of a helical VAWT, this thesis used a series of live wind tunnel tests and computational fluid dynamic simulations to measure the power output, torque fluctuation, and wake region turbulence of this type of turbine. It compared a helical VAWT with a straight bladed VAWT of the same dimensions. In addition, simulations were used to examine the turbulence in the wake region of the turbines as well as the torque fluctuation produced in the center shaft. The results showed the helical design was found to have an improvement in the power output compared to the straight bladed design and showed improved self-starting capabilities. From the CFD analysis, the helical design did not have any significant improvement in velocity recovery or in the torque fluctuation, and the helical design did only show a slight improvement in the wake region turbulence, which can translate into some noise reduction. The results of this research demonstrate how adding a helical angle to a Darrieus VAWT design improves multiple characteristics compared to its straight bladed counterpart. | |
