Contactless in-process measurement of separated flow on non-scaled rotor blades of wind turbines

例如，流动分离的可视化对于深入理解风能转子叶片的真实流动行为是必不可少的。与定标测量对象的风洞实验相比，非定标旋翼叶片上所需的非接触式现场测量尤其具有挑战性，因为测量对象的尺寸(~100 m)以及与之相关的难以接近的困难和过程中测量条件的波动。目前，流动分离测量是通过必须安装在转子叶片上或内的羊毛簇毛或压力管等标记来间接进行的。因此，这些测量方法的安装非常耗时，并且通常在空间分辨率和测量范围方面非常有限。因此，该项目的目标是基于一种新的时空评估来验证和根本表征非侵入式热像流动可视化用于识别和定位流动分离，该时空评估用于现场实际运行的风力涡轮机。该项目的重点是对热像图像进行时空信号/图像评估，以便在不对测量对象进行主动加热且不对转子叶片进行改装的情况下，实现与噪声比的充分对比。将对流动引起的时间和空间温度波动进行评估，以实现流动分离可视化所需的灵敏度改进。在现场测量这一特殊挑战的背景下，将对测量链进行建模，确定主要的测量不确定度分量，并确定热像测量方法的基本测量极限。除了低信噪比外，由于转子叶片的多轴运动，流动分离的可视化进一步复杂化。因此，计划对旋转的三维转子叶片表面进行二维图像的几何分配。例如，基于基于模型的几何校准，局部变化的成像尺度将被补偿。该测量方法将在规定条件下的风洞实验中得到验证，随后在非比例真实风力机上进行现场验证和应用，无论是在静止状态下还是在运行中。

The visualization of flow separation is essential for a deeper understanding of the real flow behavior of wind energy rotor blades, for example. In contrast to wind tunnel experiments on scaled measurement objects, the required non-contact field measurements on the non-scaled rotor blade are particularly challenging due to the measurement object size (~100 m) and the associated difficult accessibility and the fluctuating in-process measurement conditions. Currently, flow separation measurements are carried out indirectly by means of markers such as wool tufts or pressure tubes which have to be mounted on or in the rotor blade. Therefore, these measurement methods are time-consuming to install and are usually very limited with respect to the spatial resolution and the measurement field. They are also invasive and thus influence the flow behavior to be measured.Therefore, the aim of the project is to validate and fundamentally characterize the non-invasive thermographic flow visualization for the identification and localization of flow separation based on a novel spatio-temporal evaluation for the use on real-scale operating wind turbines in the field. The focus of the project is the approach of a spatio-temporal signal/image evaluation of the thermographic images in order to achieve a sufficient contrast to noise ratio despite the lack of an active heating of the measurement object and without a modification of the rotor blade. The flow-induced temporal and spatial temperature fluctuations will be evaluated to achieve the required sensitivity improvement for the visualization of flow separations. In the context of the particular challenge of a field measurement, the measurement chain will be modelled, the dominant measurement uncertainty components identified and the fundamental measurement limits of the thermographic measurement approach are determined. In addition to a low signal-to-noise ratio, the visualization of flow separation is further complicated due to the multi-axis movement of the rotor blades. Therefore, a geometric assignment of the two-dimensional image to the three-dimensional, rotating rotor blade surface is planned. Based on a model-based geometric calibration, for example, the locally varying imaging scales will be compensated. The measurement method will be verified in wind tunnel experiments under defined conditions and subsequently validated and applied in the field on a non-scaled real wind turbine, at standstill as well as in operation.