Abstract
In this study, a new type of vertical axis wind turbine (VAWT) named as Butterfly Wind Turbine had been proposed, which has armless blades consisting of a closed curve. Since a part of flow intersects the Butterfly Wind Turbine rotor four times, a new flow-field model used in BEM (Blade-Element Momentum) theory was proposed. The model was named as Quadruple-Multiple Streamtube (QMS) model, which nests the Double-Multiple Streamtube (DMS) model. Power characteristics of three kinds of VAWTs, that is, general single-straight-blade VAWT, double-straight-blade VAWT, and Butterfly VAWT, were simulated based on the BEM theory using the QMS model. The results show that, under the condition of a constant chord length, the Butterfly Wind Turbines improve the starting performance of general VAWT as well as double-straight-blade VAWTs. Furthermore, a Butterfly VAWT equipped with tapered blades shows higher power coefficient at low rotational speed condition, without significant decrease in maximum power coefficient.
