Numerical study on effects of blade tip air jet on the flow field of wind turbine blade tip

In order to design a more suitable wind turbine for the non-grid-connected wind power system, the method of arranging air jet on the blade tip was adopted to change the flow field of blade tip. Orifices were arranged on the top of the blade tip at three chordwise positions. Using the CFD numerical simulation method, the aerodynamic performances and flow field distribution of a wind turbine based model and models with orifices were obtained under different rotating speeds. When the rotating speed was below 1200r/min, all the power growth rates of wind turbine with orifices were almost zero, indicating air jet had no effect on the aerodynamic performance of wind turbines at this range of rotating speed. When rotating speed was higher than 1200r/min, with the increase of rotating speed, the power growth rates of the wind turbine with air jet at middle of the chord raised fast. The air jet affected the pressure distribution on the blade surface of 75% blade height, and the low pressure area on the suction side was larger at high rotating speed. The vorticity of blade tip vortex of the blade with air jet at middle position was lower than the other model. Meanwhile, the dissipation of the blade tip vortex was faster than that of the other model, improving the downstream flow field and the efficiency of the wind turbine. There was no obvious change when the orifice was set at the trailing edge. But for the model with orifice at leading edge, the output power declined, and the wrticity of blade tip vortex is slightly larger than the based model. This conclusion provides the foundation for designing wind turbine applicable for non-grid-connected wind power system.