We experimentally explored the effect of a series of low-level-jet (LLJ) velocity profiles on the energy entrainment of a single and a pair of counter-rotating Giromill–Darrieus vertical-axis wind turbines (VAWTs) models under two types of rotations. Planar particle image velocimetry (PIV) was used to obtain the mean flow and turbulence statistics in the wake of the model wind turbines. Incoming LLJ profiles had peaks coincident with the turbines midspan and top tip; complementary flow characterization with a canonic turbulent boundary layer is also included for comparison. Results show that the positive shear region of the LLJ velocity profiles increased the wake asymmetry due to higher vertical velocity gradients. The positive shear of the LLJ contributed to the enhancement of energy entrainment in the wake compared with a standard turbulent boundary layer profile by increasing the mean kinetic energy advection into the wake in the single and a pair of counter-rotating VAWTs. Comparatively, high vertical velocity gradients may be responsible for this phenomenon; it promoted stronger cross-flow and counter-rotating vortices in the wake.

中文翻译：

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探索低空射流对垂直轴风力涡轮机能量夹带的影响

我们通过实验探索了一系列低空射流 (LLJ) 速度剖面对两种旋转类型下单个和一对反向旋转 Giromill-Darrieus 垂直轴风力涡轮机 (VAWT) 模型的能量夹带的影响. 平面粒子图像测速 (PIV) 用于获得模型风力涡轮机尾流中的平均流量和湍流统计数据。传入的 LLJ 剖面具有与涡轮机跨中和顶部重合的峰值；还包括具有规范湍流边界层的互补流动特征以进行比较。结果表明，由于较高的垂直速度梯度，低空急流速度剖面的正切变区增加了尾流不对称性。与标准湍流边界层剖面相比，LLJ 的正切变通过增加单个和一对反向旋转 VAWT 中进入尾流的平均动能平流，有助于增强尾流中的能量夹带。相比之下，高垂直速度梯度可能是造成这种现象的原因。它在尾流中促进了更强的横流和反向旋转涡流。