Compact Wind Turbine Blade Design and Testing

The UNC Charlotte Collegiate Wind Competition team is currently participating in the 2025 Collegiate Wind Competition, and this abstract goes over the research and testing done by the blade sub team for the blade design. The three-blade configurations were selected for their aerodynamic efficiency and stability. The power is maximized at the wind speeds of 5-9 m/s since the CWC competition requirements prioritized that range of wind speed. The CWC competition also requires the entirety of the wind turbine to be able to fit in a 45x45x45 centimeter cube per competition requirements. A 20 cm blade length was chosen to maximize the swept area within competition size constraints. The current blade design uses NACA 2414 airfoil. This particular airfoil was chosen since it had a high coefficient of power relative to other NACA airfoils, and its thickness provided a blade that was structurally sound. There were also other airfoils used that were designed within the open-source blade design software, Qblade, which provided many distinct aspects to the design of the blade and the performance within different parameters. The chord and twist variation of the blades were optimized using QBlade for a TSR of 3 to maximize performance in the 5–9 m/s wind range, considering the final competition scoring rubrics. Using QBlade simulations, various pitch angles were determined to optimize power at different wind speeds. The completed blade assembly and generator were evaluated at multiple speeds and pitch angles to verify calculations. The prototype blades were 3D printed using Elegoo PLA. Various root infill percentages were assessed to determine the optimal 3D printing method moving forward. RPM and bending structural tests were performed on the prototype blades to confirm if they would perform under the specified wind loads. Structural tests proved that the blades could perform up to 1700 RPM which was the expected maximum RPM at 13 m/s. This test was accomplished through the reuse of a previous team's BLDC motor and a simple Arduino circuit created by the team electrical engineer. The team had to machine a Delrin adapter to house the 3D printed blades first. The final piece of RPM test was the pitching mechanism adapted from a KidWind wind turbine set. This allowed the team to clamp the blades securely in a timely manner with no extensive machining needed. The bending tests demonstrated that the 85% root infill blade can withstand the most force, at 12.2 Newtons, while deflecting the least, at 5.5 degrees. These preliminary tests proved that the team’s prototype blades could withstand the forces needed to create the most amount of power at various wind speeds. Testing the blade aerodynamic properties was slightly more time-consuming and required the use of QBlade. Aerodynamic testing was performed by fabricating a tower mounted turbine sitting on the rooftop of a car. The rooftop mounted turbine allowed for the team to have an environment with a consistent airflow to test which blade profile created the greatest power within competition wind specifications. The turbine’s motor was a low cogging torque drone motor, which had minimal power losses. This motor combined with the pitch system as previously stated permitted the team to assess various airfoils at the optimal pitch angles as found through the QBlade software. Utilizing QBlade, the optimal pitch for these blades to be rotated varies depending on the wind speed; however, at the maximum wind speed at which power generation will occur, 11 m/s, the pitch angle is 10 degrees. This pitch angle was determined through QBlade to maintain a consistent TSR during aerodynamic testing. The blades are mounted to the pitch system by using heat-set inserts in the root of the blade and using M3 bolts to go through the root of the blade. There are a couple of different aspects of the design that need to be improved throughout the next phase of the project, such as the heat-set insert in the root of the blade sometimes has issues being inserted into the root since excess material sets the heat-set inserts off course and causes some damage to the root. The software used to add details to the blades, such as the through holes needed for the bolt going through the root of the blade, is not efficient and has caused many problems whilst editing. Therefore, a new software must be tested and used for the rest of the project for editing the blades in an efficient manner. The blades' airfoil profile and chord length can also be optimized further through more aerodynamic testing. To improve the structural integrity of the blade the team is looking into inserting a small titanium rod the length of the chord. This paper and the presentation will also talk about the ongoing test campaign and the results observed from testing airfoils with varying chord lengths and swept areas, focusing on the wind speeds from 5-9 m/s to maximize the potential points earned per the competition ruleset. Blade root strengthening and autonomous pitching according to the wind speed will allow for the team to analyze the effects of different airfoils to a deeper degree. Throughout the short fall semester, the team delved deep into airfoil design and through this research it elevated the turbine design project in ways previous teams could not. In combination with thorough structural and aerodynamic testing, the blades created meet the theoretical goals set, and earned the team a competitive learn-along position in the competition. Moving forward, the team plans to continue rooftop car testing numerous airfoils and selecting a blade to optimize for the final stages of the competition.