浮式风力机运动形式对尾迹大尺度运动的影响

Coherent flow structures in the wake of floating wind turbines induced by motions in different degrees of freedom

为研究浮式风力机尾迹在平台运动下的演化特征和机理,本文通过线性稳定性分析和大涡模拟方法,分析了浮式风力机在纵荡、横荡和艏摇三种形式下作简谐运动时的尾迹。利用线性稳定性理论,用周向波数表示了不同运动形式引起的尾迹扰动,预测了尾迹在轴对称和非轴对称两种理想扰动下的敏感频率。稳定性分析表明:当纵荡运动的无量纲频率在0.3≤St≤0.5时最易引发尾迹失稳;横荡和艏摇运动的最敏感频率在0.2≤St≤0.4范围内;在三种运动形式下,低频(St≤0.1)和高频(St≥1.0)扰动均不会明显增长。随后,利用大涡模拟研究了不同形式、不同频率的浮式风力机刚体运动对尾迹产生的影响,检验了线性稳定性理论预报浮式风力机尾迹失稳演化的能力,并比较了不同运动形式、频率下的尾迹动态特征。研究结果表明:在St=0.3条件下,远尾迹在风力机纵荡运动下出现交替的收张运动,而在横荡、艏摇状况下将发生侧向的蜿蜒,将对下游风力机施加较大的交变载荷;在St=0.1和St=1.0的各形式运动影响下,尾迹均未发生明显的大尺度运动,不会对下游风力机的动态载荷产生明显的影响。最后,从风力机尾迹演化的角度讨论了浮式风力机设计中应重点考虑的刚体运动形式和频率范围,指出应慎重评估无量纲频率在St=0.3附近的风力机运动对尾迹演化的作用。

Accurate prediction of wake flows is essential for wind turbine structure design and wind farm layout optimization.This paper investigates floating offshore wind turbines'wake flows induced by the surge,sway,and yaw of platforms by employing the linear stability theory and large-eddy simulations.Perturbations induced by different motions are represented by different circumferential wavenumbers in the stability analysis.The analysis shows that the wake flows are the most unstable when the dimensionless frequency ranges from 0.3≤St≤0.5 for surge motion and 0.2≤St≤0.4 for sway and yaw motions.No apparent amplification is found for low-frequency(St≤0.1)and high-frequency(St≥1.0)disturbances regardless of motion types.The large-eddy simulation confirms the results of the stability analysis.At St=0.3,the surge motion leads to periodic contraction and expansion of the wake flow,while the other two motions result in lateral meandering that may induce large unsteady loads for downstream turbines.On the other hand,motions at St=0.1 and St=1.0 do not lead to apparent large-scale wake motions,yielding negligible unsteady loads for downstream turbines.Consequently,special attention is required to platform motions around St=0.3 due to their potential hazards on downstream turbines.