2017 Volume 12 Issue 1 Pages JFST0005
The operating conditions of Horizontal Axis Wind Turbine (HAWT) are extremely complex in natural surroundings. One of the wind conditions is called extreme wind direction change which has been specified in the International Electrotechnical Commission (IEC) 61400-1 standard. External conditions can generate extreme loads which may affect the power coefficient and the lifetime of HAWTs. This paper attempted to compile the evaluation of the aerodynamic forces acting on a small HAWT under extreme wind direction change condition in the wind tunnel experiments. An Avistar airfoil is used for the two-bladed and three-bladed wind turbines. This study is intended to clarify the load fluctuation when sudden wind direction change reacts to two-bladed and three-bladed wind turbines. A vane system is used to generate the wind direction change. A 6-component balance is used to measure the forces and the moments acting on the entire wind turbine in the three directions of x, y and z-axes. The results show that when the extreme wind direction change is generated, the yaw moment fluctuation amplitude of two-bladed wind turbine is about 39% larger than that of the three-bladed one. The strong dependence of the inflow timing of the wind direction change on the fluctuation amplitude can be seen only for the two-bladed wind turbine.