The following are more features that make this design superior, as well as further questions and avenues of research for further testing and optimization.
The involute spiral has unique properties that, when applied to the vanes of a vertical axis wind turbine (VAWT) generate considerable shaft-power in relatively low winds. Over the past 37 years, I have built and tested several prototypes, but have done little controlled testing; measuring power and rotational speed relative to wind speed, power extraction, number of vanes of varied curvature and other variables that would help optimize design features for different applications. Further prototype testing, in the field and in a wind tunnel, as well as computer simulation flow analysis could shed light on this optimization process.
Several unique design features raise significant questions about the flow of wind through this turbine.
In this Involute-vaned VAWT, the wind flows through several non-constricting spiral channels into the center, then out the back, imparting lift and push (drag) throughout. The involute vanes act like an ideal venturi shroud, diverting the wind mass continually inward to the central hole, then outward into a low pressure leeward zone.
The Enflo Windtec shrouded turbine achieved over twice the power from a 12.5m/sec wind as a comparable unshrouded blade turbine. This suggests a potential for comparable efficiencies through the involute spiral vanes of this VAWT technology, but with a much lighter, simpler design. Because the power of the wind is transferred to the vanes as it is spirals through, reducing the speed of the wind to the lee of the turbine, thus deflecting the wind outside the turbine inward downstream, this turbine may gain power from adjacent air outside the turbine wind shadow as well. This is in contrast to a conventional airfoil-blade horizontal axis wind turbine (HAWT), which throws the wind outward into a turbulent zone. This does not contradict Betz’s 59% maximum efficiency calculations, because that Law doesn't apply to this 3D power profile. Betz’s Law is based on extracting the power of the wind from a flat plane where the propeller blades rotate. The geometry of this Involute VAWT is quite different from that, with orders of magnitude greater surface area pulling the wind into the center, while extracting with the airfoil curved vanes both lift and drag power continuously, both entering and exiting the depth of this spinning top.
Betz’ law is based on analysis of fluid flow through a disk-shaped actuator, whereas this VAWT has active energy transfer throughout the volume of the cylinder or cone of impeller surface. The actual flow and pressure profiles of this shape are complex and need to be further simulated and tested. For instance, what is the pattern of wind flow through the central circular open area? It seems to flow through smoothly, even at high speeds, perhaps forming a spinning cyclone that flows automatically to the lowest pressure. Is it possible to harness the wind, not just passing through the vanes, but also in the vicinity of the turbine to increase the power density transferred to the turbine? If this is so, and downstream non-turbulent low pressure air would seem to invite such acceleration, do we call this “over-unity” power? In addition to the Enflo Windtec shrouded turbine, one new shrouded HAWT, the Wind Tamer, claims to have exceeded Betz’s law already.
State-of-the-art computer flow-analysis software could reveal valuable new wind-turbine flow parameters and design data. This could make an excellent research project for a grad student seeking to learn more about the physics of fluid flow, fundamentals of VAWT design, and be in on the development of an exciting new wind turbine technology.
Here is an excellent article on the large niche markets for this new breed of wind turbine:
Here is a Distributed Energy online magazine article on small wind turbines titled, “Tipping Point”.