垂直轴风力机气动特性与涡脱落模态分析

AERODYNAMIC CHARACTERISTICS AND VORTEX SHEDDING MODAL ANALYSIS OF VERTICAL AXIS WIND TURBINE

垂直轴风力机运行过程中,叶片上下表面边界层与剪切层的相互作用使风力机下游尾迹形成周期性涡结构,这种尾迹涡结构对风力机空气动力学特性具有重要影响。基于此,该文采用计算流体力学方法对不同工况下垂直轴风力机尾迹涡结构展开研究,利用快速傅里叶变换与相空间轨迹分析不同尖速比下风力机叶片涡脱落现象和尾迹涡结构,并通过分形维数研究转矩与尾迹流场速度变化。结果表明:风力机尾迹涡结构随尖速比变化呈现不同特征,当尖速比为3.6时,风力机尾迹两侧呈规则性反向脱落涡模态;低尖速比垂直轴风力机尾迹具有明显的混沌特性,且随尖速比的增加混沌特性逐渐减弱;随着尖速比的增加,风力机转矩与下游速度分形维数不断降低,且当尖速比为3.6时,风力机下游速度分形维数仅为1.07。

During the operation of a vertical axis wind turbine,the interaction between the upper and lower surface boundary layer and the shear layer causes the formation of periodic vortex structure in the downstream wake of the wind turbine,which has an important effect on the aerodynamic characteristics of the wind turbine. Based on this,the CFD method is used to study the wake vortex structure of vertical axis wind turbine under different working conditions. Fast Fourier transform and phase space trajectory are used to analyze the vortex shedding phenomenon and wake vortex structure of wind turbine blade under different tip speed ratios. The fractal dimension is used to study the torque and wake flow velocity variation. The results show that the wake vortex structure of the wind turbine presents different characteristics with the change of the tip speed ratio. When the tip speed ratio is 3.6,the two sides of the wind turbine wake show regular reverse shedding vortex mode. The wake of the vertical axis wind turbine with low tip ratio has obvious chaotic characteristics,and the chaotic characteristics gradually weaken with the increase of the tip ratio. With the increase of the tip speed ratio,the fractal dimension of wind turbine torque and downstream speed decreases continuously,and when the tip speed ratio is 3.6,the fractal dimension of downstream speed of wind turbine is only 1.07.