ABSTRACT
A wind energy converter’s economy is dependent on the precision, reliability and redundancy of its control, its ease of transportation to, and remote places of installation, and its lifetime with respect to fatigue as well as attrition. So not only aerodynamically possible high efficiencies, but also the feasibility of constructing and controlling with ease very large rotors, extremely high specific speeds at satisfactory efficiencies. A rotor’s actual data, plotted for a number of given general pitches versus the speed ratio and called the rotor characteristics, define its qualities. The result of the valuation is that, up to specific speeds where other limitations turn out to be essential, rotors with higher optimum rated speeds are doubtless by far the best solution. As the vortex ring is unstable with respect to its position, it is constantly renewed by the rotor tip and fades away into the discontinuous vortex sheet that separates the free flow from the wake of the rotor’s inner part.
