Performance Evaluations of Straight Darrieus Type Wind Turbine Appended inner Bach - Comma Shaped Rotor

Abstract

The straight Darrieus type wind turbine, which is expected to use for dispersed power source in urban site, has low performance especially at low tip speed ratio. In this paper, we suggested new type inner rotor to increase the power coefficient over wide range of tip speed ratio. The new type inner rotor, called “Bach – Comma shaped rotor”, is consist of a combination with cylindrical outer shape and Bach type inner shape. The Bach type shape has straight part to gain more torque from the wind than the classical Savonius bucket. The outer cylindrical shape inhibit the flow separation on the blade and rise the power coefficient. It was verified that the “Bach – Comma shaped rotor” is valid for increase the power coefficient over wide range of tip speed ratio by performing both two-dimensional numerical simulations of flow and the torque measurement experiments under the wind-tunnel.