风力机翼型在复合运动下的动态失速数值分析

NUMERICAL INVESTIGATION ON DYNAMIC STALL OF WIND TURBINE AIRFOIL UNDERGOING COMPLEX MOTION

现代大型风力机在工作时叶片经历大变形与振动,将会对其周围的动态流场产生影响,从而导致气动力的改变。因此有必要深入研究风力机翼型在复合运动情况下的动态失速气动特性,以正确预测大型风力机运行时的载荷。该文应用计算流体力学方法,对S809翼型在不同运动形式下的动态失速特性进行了二维数值分析。首先对翼型在作俯仰运动下的轻失速和深失速情况分别结合S-A、SST k-?和RSM三种湍流模型进行了动态失速数值模拟,结果表明S-A、SST k-?和RSM三种湍流模型都能有效地计算出翼型的气动力。然后采用SST k-?模型仿真了翼型在挥舞运动、俯仰摆振耦合运动下的动态失速气动特性,并与相同工况条件下翼型作俯仰运动时的气动特性进行了对比分析。发现翼型在挥舞运动下的动态失速虽然弱于俯仰运动,但其强度不容忽视;而翼型在作俯仰与摆振耦合运动时比单纯作俯仰运动时的失速程度更深。因此在风力机设计阶段为获得保守的气动载荷预测,有必要将叶片截面在挥舞与摆振方向的运动转换成等效攻角,叠加在主攻角上进行动态失速气动力计算。

The blade of large-scale wind turbine undergoes significant deflection and vibration during operation, which will impact the dynamic flow field around the blade and consequently alter the aerodynamic forces. Therefore, it is important to develop a deep understanding of the dynamic stall characteristics of airfoil undergoing complex motion, so that the operational loading of large-scale wind turbines can be accurately predicted. Applying computational fluid dynamics（CFD） techniques, this paper presents 2-dimensional numerical simulations of the dynamic stall characteristics of S809 airfoil undergoing different forms of motion. Firstly the dynamic stall behavior of the airfoil undergoing pitching motion in stall-development and deep-stall regimes is simulated using S-A, SST k-？ and RSM turbulence models. Comparisons with the experimental measurements indicate that all the three turbulence models can effectively predict the unsteady aerodynamic forces of the airfoil. Subsequently, the dynamic stall characteristics of the airfoil undergoing flapwise motion and combined pitching edgewise motion are simulated using SST k-？ model. The results are compared with those obtained by considering only pitching motion in the same condition. The dynamic stall of airfoil undergoing flapwise motion is weaker than that of airfoil undergoing pitching motion, but it is considerable and cannot be neglected. The dynamic stall of airfoil undergoing combined pitching edgewise motion is much stronger than that of airfoil undergoing pitching motion. The results suggest that in the design stage of a wind turbine, in order to obtain a conservative aerodynamic loading prediction, it is necessary to translate the motion of the blade cross-section in flapwise and edgewise directions into an equivalent angle of attack, and superimpose it on the main angle of attack to perform the dynamic stall calculation.