During 1970's, the late professor Thomas E. Sweeney of Princeton University developed his well known Princeton Sailwing Concept aimed toward the wing for subsonic applications as well as wind turbine design. He had also proposed a concept of vertical-axis wind turbine driven by drag/lift force, having rotor of elliptical cross section with fins at both edges. However, he had not been conducted the test on his unique machine, until now, the performance data of Sweeney type vertical-axis wind turbine has not been presented. One of the authors conducted a wind tunnel test of the Sweeney type wind turbine and reported the basic performance of this machine.(Maximum power coefficient Cpmax=0.052 was obtained at tip speed ratio λ=0.4.) The authors manufactured Twisted-Sweeney type wind turbine, based on Sweeney type wind turbine, to improve the performance and to enhance the beauty of external appearances. In this research, the authors carried out model tests in a wind tunnel in order to confirm the performance of Sweeney type and Twisted-Sweeney type wind turbines. As a result, the following facts were obtained. (1) In the case of twisting 90 degrees from the top to the bottom of the Sweeney type wind rotor, the power coefficient of Twisted-Sweeney type wind turbine is increased even at low wind velocity.(Maximum power coefficient Cpmax=0.06 was obtained at tip speed ratio λ =0.35.) (2) In the case of adding curvature of “S” shape to cross section of the Sweeney type wind rotor, the tip speed ratio and the power coefficient increased, and the operational range of tip speed ratio is widened.(Maximum power coefficient Cpmax=0.1 was obtained at tip speed ratio λ=0.5.) (3) The maximum power coefficient of Twisted-Sweeney type wind turbine with twist and curvature is about 23 times higher than that of Sweeney type.(Maximum power coefficient Cpmax=0.12 was obtained at tip speed ratio λ =0.5.) (4) The maximum power coefficient of Twisted-Sweeney type wind turbine with end plates is 1.5 time higher than that without end plates.(Maximum power coefficient Cpmax=0.18 was obtained at tip speed ratio λ=0.75.)
Everyone involved in the field of wind energy research and utilization is familiar with the so-called Betz limit. It defines an upper limit to the amount of energy in the wind that can be converted to effective power. The original derivation of this limit has been attributed to Albert Betz, a pupil and colleague of Ludwig Prandtl at Goettingen University in Germany. However, the English engineer Frederick William Lanchester published more than five years before exactly the same result as derived later by Betz. And yet, there is no reason to believe that Betz would deliberately to acknowledge Lanchester's earlier derivation if he was aware of it. It is interesting to consider whether or not the earlier deviation might have been known to Betz. In view of the circumstances affected by World War I, the authors propose that the so-called Betz limit be referred to in the future as the Lanchester-Betz limit. For Lanchester, it will be a well deserved tribute to a scientist who helped lay the foundation for our present understanding of wind turbine rotor aerodynamics.