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涡轮(BERT)的负荷减轻方法，并分析局部不稳定和旋转的影响。在第一阶段，BERT是在德国柏林工业大学大型风洞的4.2m x 4.2m风力机试验段设计、建造和安装的。所有数据采集和控制硬件都安装在旋转系统(集线器)内部。这一独特的设施是德国第一个风洞中的负载控制研究涡轮机，具有高可用性和低运营成本的优势，这是科学研究的最佳性能。BERT还允许开发一种新的测量技术，其中定量簇流可视化技术与时间分辨压力和振动测量同步。利用这项技术，可以将任意测量变量(例如压力)与转子叶片上的瞬时表面流场联系起来。它可以在一张图像中捕捉到完整的转子，所有三个叶片都配备了流束和图像配准标记。这种方法对于分析风力机叶片上的非定常流动现象和载荷是很有帮助的。到目前为止，该项目的重点是大范围的流入扭曲，如速度剪切和偏航偏差。这些非定常流动条件也存在于大型风力涡轮机上。随着叶片长度的不断增加，在叶片载荷谱中，沿跨距的局部流入变形占主导地位。在第一阶段，非定常流入条件是通过驱动涡轮进入高达30度的偏航偏心而产生的。在项目的第二阶段，将提高流入条件的复杂性，以探索PP 2[Nayeri/Paschereit]的负载控制概念伺服襟翼和PP 5[Tropea]的自适应弧度的局限性。流入扭曲现在将由旋翼平面上游的速度差(尾迹)局部产生。当旋翼叶片通过尾流区时，进气速度和攻角会同时发生变化。这代表典型的失真或典型的阵风，相应的负载控制系统将对其做出反应。通过改变尾迹速度差来获得三个迎角/速度的变化。然后将在类似的流入条件下比较PP 2[Nayeri/Paschereit]和PP 5[Tropea]的负载控制概念。实验结果将与PP 3[Lutz/Krämer]中进行的数值模拟进行比较。除了测试在其他类似流入扭曲下的载荷控制概念外，还计划研究3D或旋转效应对(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/或迎角以谐和的方式变化时，产生的非定常升力会偏离相应的准定常升力。

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.