In the main tidal energy sites like Alderney Race, turbulence intensity is high and velocity fluctuations may have a significant impact on marine turbines. To understand such phenomena better, a three-bladed turbine model is positioned in the wake of a generic wall-mounted obstacle, representative of in situ bathymetric variation. From two-dimensional Particle Image Velocimetry planes, the time-averaged velocity in the wake of the obstacle is reconstructed in the three-dimensional space. The reconstruction method is based on Proper Orthogonal Decomposition and enables access to a representation of the mean flow field and the associated shear. Then, the effect of the velocity gradient is observed on the turbine blade root force, for four turbine locations in the wake of the obstacle. The blade root force average decreases whereas its standard deviation increases when the distance to the obstacle increases. The angular distribution of this phase-averaged force is shown to be non-homogeneous, with variation of about 20% of its time-average during a turbine rotation cycle. Such force variations due to velocity shear will have significant consequences in terms of blade fatigue. This article is part of the theme issue ‘New insights on tidal dynamics and tidal energy harvesting in the Alderney Race’.

中文翻译：

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基于三维平均流重构的剪切流对潮汐涡轮叶片根部力的影响实验分析

在像奥尔德尼赛这样的主要潮汐能源站点，湍流强度很高，速度波动可能对船用涡轮机产生重大影响。为了更好地理解这种现象，在一般壁挂式障碍物之后放置了一个三叶涡轮机模型，代表原位测深变化。从二维粒子图像测速平面，在三维空间中重建障碍物尾迹的时间平均速度。重建方法基于适当的正交分解，可以访问平均流场和相关剪切的表示。然后，观察速度梯度对涡轮叶片根部力的影响，对于障碍物尾流中的四个涡轮位置。当与障碍物的距离增加时，叶片根部力平均值减小，而其标准偏差增加。该相位平均力的角度分布被证明是不均匀的，在涡轮机旋转周期中其时间平均值的变化约为 20%。由于速度剪切引起的这种力变化将对叶片疲劳产生重大影响。本文是主题问题“奥尔德尼岛竞赛中潮汐动力学和潮汐能收集的新见解”的一部分。