Prediction of Aerodynamic Characteristics of the Wing Stroke Mechanism in Lower Tip-Speed Ratio Condition

Abstract

The author previously developed a wing stroke mechanism WSM as a human-friendly wind apparatus suitable for distributed power generation system in urban areas. The results of the operation in various kinds of wind condition and the result of the computer simulation show a clear tendency for the tip-speed ratio of the system to remain around one or two. The operation under very low tip-speed ratio condition with single or twin blade(s) may suggest that, different from normal horizontal axis wind turbine (HAWT), the azimuthal variation of the wake in the rotor can not be ignored. In addition, the influence of the interference between contra rotating twin blades in one rotor disc requires special calculation based on vortex theory. In this paper, the basic aerodynamic characteristics of the wind-stroke mechanism are investigated utilizing the lifting line theory. The fundamental integral equation is led and solved numerically using MATLAB and Simulink. Successive parametric research is undertaken according to parameters like aspect ratio sweepback angle taper-ratio and the asymmetry of the wing section of rotor blade(s). The wing stroke mechanism (WSM) has sweep back angle in order to get the directional stability. If the blade(s) with sweep back angle rotates, it makes a cone with a coning angle as is conventionally defined on HAWT. Considering again that the tip-speed ratio of the operating single or twin blade(s) is very small, it is preferable to apply the lifting line theory instead of common blade element momentum theory even though recently much improvement is established for that kind of complexity. The result shows that the wing stroke mechanism has a mixed character of the fixed wing of the airplane and the rotating blade(s) of HAWT.