I made a post not too long ago about a design for a home built wind turbine. Since then, I have kicked around a few ideas about what this design needs to achieve. One requirement that I added is that it needs to be safe for birds. Wind turbines pose a significant risk for birds since they are usually mounted high in the air, and have large quickly rotating elements that can strike birds that are unaware of the danger. One solution for this problem could be to impliment a turbine design that has slower rotating elements. One such design is a Savonius style turbine.
The savonius turbine uses large blades that rotate about a vertical axis. They are omni-directional, and therefore don’t require machinery to aim the turbine into the prevailing wind direction. The disadvantage to this turbine design is that there is a loss of efficiency. The savonius turbine does not maintain laminar flow over the blades, which conventional turbines do. This creates large, significant vortices trailing behind the turbine, which also means that there is increased distance required between multiple turbines placed together.
One can implement a number of techniques to increase the efficiency. One paper used computational fluid models to deduce an ideal blade shape for a savonius turbine (Tian et al.). Other experiments determined that two blades are the most efficient, and deduced other geometrical optimizations for the design. The results (according to these sources) indicate that an ideal savonius turbine has two blades, has an gap ratio of 1/6 * radius, an overlap ratio of 0, a phase angle of 45 degrees, and incorporates end plates . The phase angle for best efficiency is zero, however the ability to self start is sacrificed in that instance, so 45 degrees is used as a compromise (Chen et al.) (Jian et al.).
What about the 3D printing?
What I’ve done here is design a turbine blade element and base that can be additively manufactured and furthermore expanded so that they can be stacked to different heights, or aspect ratios. As a side note, higher aspect ratios are associated with higher efficiency.
The above is my attempt to incorporate all of those parameters into a blade design. This design is designed to be stackable and wedged between two end plates. The 45 degree sweep is intended to make it able to self start with any wind direction. The blade design is 250mm in length, making the constructed turbine 0.5m in total diameter.
Designing the end plates will be the next phase of the project.
Chen, Liu, et al. “Wind Tunnel Investigation on the Two- and Three-Blade Savonius Rotor with Central Shaft at Different Gap Ratio.” Journal of Renewable and Sustainable Energy, vol. 8, no. 1, Jan. 2016, p. 013303, 10.1063/1.4940434. Accessed 21 Oct. 2019.
Jian, Chen, et al. “Influence of Phase-Shift and Overlap Ratio on Savonius Wind Turbine’s Performance.” Journal of Solar Energy Engineering, vol. 134, no. 1, 1 Dec. 2011, 10.1115/1.4004980. Accessed 22 Oct. 2019.
Tian, Wenlong, et al. “Shape Optimization of a Savonius Wind Rotor with Different Convex and Concave Sides.” Renewable Energy, vol. 117, Mar. 2018, pp. 287–299, 10.1016/j.renene.2017.10.067. Accessed 21 Oct. 2019.