Experimental assessment of active flow control techniques for wind turbines with a wind tunnel Demonstrator

第二个资助期的总体目标是继续研究柏林研究汽轮机（BeRT）的减载方法，并分析局部失稳和旋转的影响。第一阶段，BeRT在柏林工业大学大型风洞4.2 m × 4.2 m风力机试验段进行设计、建造和搭建。所有数据采集和控制硬件都安装在旋转系统（轮毂）内。这种独特的设备是德国第一个风洞负载控制研究涡轮机，具有高可用性和低运行成本的优点，是科学研究的最佳性能。BeRT还开发了一种新的测量技术，将一种定量的簇状流动可视化技术与时间分辨压力和振动测量同步。使用这种技术，可以将任意测量的变量（例如压力）与转子叶片上的瞬时表面流场联系起来。可以在一张图像中捕获完整的转子，所有三个叶片都配备了流簇和图像配准标记。该方法对风力机叶片非定常流动现象和负荷分析具有重要意义。到目前为止，该项目的重点是大规模的流入扭曲，如速度剪切和偏航失调。这些非定常流态也存在于大型风力发电机上。随着动叶长度的不断增加，沿跨段的局部入流畸变在叶片载荷谱中占据主导地位。在第一个阶段，通过将涡轮驱动到偏航偏差达30度产生非定常流入条件。在项目的第二阶段，将提高入流条件的复杂性，以探索PP 2的伺服驱动襟翼[Nayeri/Paschereit]和PP 5的自适应弧度[Tropea]的负载控制概念的局限性。现在，流入畸变将由旋翼平面上游的速度亏缺（尾迹）局部产生。当动叶穿过尾迹区时，来流速度和迎角都会同时发生变化。这代表了各自的负载控制系统将对其作出反应的典型扭曲或典型阵风。尾流速度亏损将被改变以获得三个攻角/速度变化。然后将在类似的流入条件下比较PP 2 [Nayeri/Paschereit]和PP 5 [Tropea]的负荷控制概念。实验结果将与在PP 3环境下进行的数值模拟进行比较[Lutz/Krämer]。除了在其他类似的流入扭曲下测试负载控制概念外，还计划研究3D或旋转对（非定常）升力产生的影响。众所周知，当二维机翼的入流速度和迎角发生谐波变化时，产生的非定常升力会偏离各自的准定常升力值。

The global goal of the second funding period is to continue the investigations of load alleviations methods on the Berlin Research Turbine (BeRT) and to analyze the influence of local unsteadiness and rotation. During the first period, BeRT was designed, constructed and set up in the 4.2 m x 4.2 m wind turbine test section of the TU Berlin large wind tunnel. All data acquisition and control hardware is installed inside the rotating system (hub). This unique facility is the first German load control research turbine in a wind tunnel with the advantages of high availability and low operational costs which are optimal properties for scientific studies. BeRT also allowed the development of a novel measurement technique where a quantitative tuft flow visualization technique was synchronized with time resolved pressure and vibration measurements. With this technique, an arbitrary measured variable (e.g. pressure) can be linked to an instantaneous surface flow field on the rotor blades. It is possible to capture the complete rotor in one image, with allthree blades equipped with flow tufts and image registration markers. This method is very helpful for analyzing unsteady flow phenomena and loads on wind turbine blades. So far, the project was focused on large-scale inflow distortions such as a velocity shear and yaw misalignment. These unsteady flow conditions are also found on large scale wind turbines. With ever-increasing rotor blade lengths, the local inflow distortions along the span become dominant in the blades load spectrum.In the first period, the unsteady inflow conditions were generated by driving the turbine into a yaw misalignment of up to 30 degrees. In the second period of the project, the inflow conditions complexity will be raised to explore the limitations of the load control concept servo-actuated flaps of PP 2 [Nayeri/Paschereit] and adaptive camber of PP 5 [Tropea]. The inflow distortion will now be generated locally by a velocity deficit (wake) upstream of the rotor plane. As the rotor blade passes through the wake-region, both inflow velocity and angle of attack will be altered simultaneously. This represents a typical distortion or a typical gust to which the respective load control system will react. The wake velocity deficit will be varied to obtain three angle of attack/velocity variations. The load control concepts of PP 2 [Nayeri/Paschereit] and PP 5 [Tropea] will then be compared under similar inflow conditions. The experimental results will be compared to numerical simulations conducted within the context of PP 3 [Lutz/Krämer].In addition to testing the load control concepts under otherwise similar inflow distortions, it is also planned to study the effect of 3D, or rotational, effects on the (unsteady) lift generation. It is known that when the inflow velocity and/or angle of attack of a 2D wing is varied in a harmonic manner, the generated unsteady lift deviates from the respective quasi-steady lift value.