There were many challenges to the Spring 2014 Wind Blade Project. Not all CAD designs will 3D-print as expected since the process is very dependent on the quality of the printer itself and the mechanical imperfections that the printer may experience during a particular session, which is affected by the printing parameters (speed of printing, layer thickness, density or hollowness of the part, among others). Many times the extruder of the printer would get stuck or overheat and the incorrect amount of melted plastic would come out, thus altering the part dimensions and design. Another issue was the sliding of the part off of the platform which ended up invalidating the part completely. By doing online research and ultimately utilizing some physics, chemistry, and engineering basic concepts, students learned that these problems could be solved sometimes by choosing the correct combination of printing parameters for their particular design, and other times by modifying their CAD design and/or dimensions to be printed out. Unlike in Fall 2013’s car project, where the finishing of the parts where mostly a cosmetic matter, in this Wind Blade Project, a small alteration in the dimensions, geometry, and surface’s smoothness had an impact on the performance of the blade.
The main engineering design requirement was to have a maximum rotor blade diameter of 120mm, so all the rotors look similar in that respect. The criteria to win the competition was to obtain the best performance (harvest most energy by measuring the back-emf out of a small generator) at a wind’s low speed of 4.5m/s and a medium speed of 6.7m/s measured in the wind tunnel at the lab. There were no restrictions on the depth/thickness/number of blades, nor the weight; but the students quickly found out that there was a trade off between having more blade surface (or number of blades) and making the rotor lighter in order for their design to perform better. Other design decision was to come up with an ideal airfoil (blade’s cross section) and its corresponding parameters like the angle of attack, among others that may require advanced knowledge in aerodynamics and fluid mechanics in order to obtain the more efficient design for the constraints given. However for this, the students were given the liberty to utilize tables, spreadsheets, and even software available online to come up with their ideal airfoil, as is the case in a real-life engineering design process. Most groups chose 3 blades but there were groups with 2, 4, and even 5-blade designs. The airfoils were definitely all different as there are basically infinite ways of combining airfoil parameters.
It’s worth to mention that, although the rotors may look similar, there were huge differences in the energy harvested. For example, the 1st place design generated 20% more energy than the 2nd place design, and about 300% more than the 12th place design.