The journey of BiomeRenewables' PowerConeTM wind turbine started with witnessing a falling maple seed. I was sitting on my deck when I was struck by how slowly the seed was able to fall. As it turns out, maple seeds — for their size — exhibit maximum aerodynamic efficiency; they are able to hit what is known as the Betz Limit — 59.3 percent aerodynamic efficiency. Careful analysis revealed that there is something about the seed’s shape and the way it interacts with the air that allows it to achieve such high efficiency numbers — namely, that it interacts with the oncoming flow at an angle greater than 90 degrees. This is not the case with modern wind turbines, which interact with the wind at perpendicular angles of 90 degrees.
Starting it up
I soon realized that there was an extraordinary opportunity for this bio-based geometry. We could create a device with three troughs, each with angles matching that of the maple seed, and place it in the center of the turbine. The phenomena of “rotor root leakage” in wind turbine blade design has plagued the industry for decades. The vast majority of rotor blades have a cylindrical root at the center that confers little to no aerodynamic advantage to the turbine — in fact it hinders it, causing a pressure imbalance across the rotor disk which leads to a multitude of other problems for wind farm owners. By covering some of this area and shunting flow radially towards the suction side of the blade, we can confer more aerodynamic efficiency to the turbine.
Through various small-scale prototypes set in real-world wind conditions and controlled wind tunnels, my BiomeRenewables team succeeded in demonstrating what the PowerCone was capable of: industry leading performance, at least at small scale. The PowerCone was producing annual energy production (AEP) increases of more than 10 percent, as well as improving the capacity factor, turbine cut-in and loading conditions.
Throughout this period of development, 1:50th scale models tried to simulate as closely as possible how the PowerCone would perform at full scale. This meant paying attention to points of friction, materials and tip speed ratios — the ratio of the blade tip velocity to incoming wind velocity. In addition to this, Reynolds numbers become important in assessing the validity of any experiment. While it is possible to account for tip speed ratios in scaled models, Reynolds numbers (which describes in broad terms how fluids behave across scales) are inputs that can only be determined for certain at our final full scale. Aerodynamics is a tricky and sometimes counter-intuitive business: fluid-dynamics is considered one of the hardest branches of the physical sciences to master, let alone understand! That’s where computers can help.
Scaling it up
Before mounting the PowerCone on an actual wind turbine and incurring the associated risks, we at BiomeRenewables wanted to understand how the wind would interact with the PowerCone-enabled wind turbine at full scale, and if the small-scale performance would carry over. This is where ANSYS CFX software, obtained through the ANSYS Startup Program, became particularly useful. This software enabled BiomeRenewables’ engineering team to model the prototype in a variety of wind conditions with rotating domains and a mesh resolution equivalent to 75 million cells, producing extremely detailed analysis of flow patterns, vortex formation and boundary layer effects in record time. Through this process, we realized that we could extract even more performance from the PowerCone by altering its geometry, amplifying torque production and strengthening our business case.
Through the ANSYS Startup Program, BiomeRenewables was able to leverage a highly iterative design process to increase the performance of our flagship product offering and minimize the risk of the entire project to investors and the wind community at large. We are now in the process of planning a full-scale demonstration of the PowerCone technology, with commercial partners waiting eagerly for results.