The wake produced by a model wind turbine is investigated using proper orthogonal decomposition (POD) of numerical data obtained by large eddy simulations at a diameter‐based Reynolds number . The blades are modeled employing the actuator line method and an immersed boundary method is used to simulate tower and nacelle. Two simulations are performed: one accounts only for the blades effect; the other includes also tower and nacelle. The two simulations are analyzed and compared in terms of mean flow fields and POD modes that mainly characterize the wake dynamics. In the rotor‐only case, the most energetic modes in the near wake are composed of high‐frequency tip and root vortices, whereas in the far wake, low‐frequency modes accounting for mutual inductance instability of tip vortices are found. When tower and nacelle are included, low‐frequency POD modes are present already in the near wake, linked to the von Karman vortices shed by the tower. These modes interact nonlinearly with the tip vortices in the far wake, generating new low‐frequency POD modes, some of them lying in the frequency range of wake meandering. An analysis of the mean kinetic energy (MKE) entrainment of each POD mode shows that tip vortices sustain the wake mean shear, whereas low‐frequency modes contribute to wake recovery. This explains why tower and nacelle induce a faster wake recovery.

中文翻译：

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塔架和机舱影响下基于POD的风轮机尾流分析

使用基于直径雷诺数的大型涡流模拟获得的数值数据的适当正交分解（POD），研究了模型风力涡轮机产生的尾流 。叶片采用执行器线法建模，沉浸边界法用于模拟塔架和机舱。进行了两种模拟：一种仅说明叶片效果；另一种仅说明叶片效果。另一个还包括塔楼和机舱。根据平均流场和主要表征尾流动力学的POD模式对这两种仿真进行了分析和比较。在仅转子的情况下，近尾流中最强的能量模式由高频尖端和根部涡流组成，而在远尾流中，发现了考虑尖端涡流互感不稳定性的低频模式。如果包括塔架和机舱，则低频POD模式已经在近身时出现，与塔架散发出的von Karman涡流有关。这些模式与远处的尖端涡旋非线性相互作用，产生新的低频POD模式，其中一些处于尾波曲折的频率范围内。对每种POD模式的平均动能（MKE）夹带的分析表明，尖端涡流维持了尾流的平均剪切力，而低频模式则有助于尾流的恢复。这解释了为什么塔架和机舱会导致更快的尾流恢复。