Computational Fluid Dynamics Analysis of Floating Offshore Wind Turbines in Severe Pitching Conditions
Computational Fluid Dynamics Analysis of Floating Offshore Wind Turbines in Severe Pitching Conditions
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DOI：
10.1115/1.4048776
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发表时间：
2020-11
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影响因子：
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通讯作者：
A. Ortolani;G. Persico;J. Drofelnik;A. Jackson;M. Campobasso
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作者：
A. Ortolani;G. Persico;J. Drofelnik;A. Jackson;M. Campobasso
浮式风力涡轮机的非定常空气动力学比固定底部涡轮机的非定常空气动力学更复杂，并且对于浮式涡轮机，低保真度预测的不确定性更高。Navier-Stokes计算流体动力学（CFD）可以提高对浮式涡轮机转子和尾流空气动力学的理解，并有助于改进较低保真度的模型。在这里，NREL 5 MW转子的流场与固定的塔，并进行规定的谐波俯仰过去的塔基使用叶片解析的CFD可压缩流COSA模拟和不可压缩流FLUENT模拟研究。计算流体动力学的结果也进行了比较，预测的快速风力涡轮机代码，其中使用叶片元素动量理论（BEMT）。所选的转子变桨参数对应于在没有涡轮机安全系统故障的情况下不太可能发生的极端状态，因此与极端气动载荷分析相关。计算流体动力学程序和BEMT预测的固定塔模式下的转子功率和载荷非常一致。对于浮动式涡轮机，转子功率和推力的所有预测周期性曲线在性质上相似，但两种CFD预测的功率峰值明显高于BEMT预测的峰值。此外，COSA和FLUENT叶片静压预测的交叉比较也突出了可压缩流对转子功率和负载的显著影响。下游转子流的CFD分析还揭示了变桨涡轮机特有的尾流特征，主要是尾流产生强度的空间和时间依赖性，突出表现为叶尖涡脱落的不稳定性。
The unsteady aerodynamics of floating wind turbines is more complex than that of fixed-bottom turbines, and the uncertainty of low-fidelity predictions is higher for floating turbines. Navier–Stokes computational fluid dynamics (CFD) can improve the understanding of rotor and wake aerodynamics of floating turbines, and help improving lower-fidelity models. Here, the flow field of the NREL 5 MW rotor with fixed tower, and subjected to prescribed harmonic pitching past the tower base are investigated using blade-resolved CFD compressible flow COSA simulations and incompressible flow FLUENT simulations. CFD results are also compared to predictions of the FAST wind turbine code, which uses blade element momentum theory (BEMT). The selected rotor pitching parameters correspond to an extreme regime unlikely to occur without faults of the turbine safety system, and thus relevant to extreme aerodynamic load analysis. The rotor power and loads in fixed-tower mode predicted by both CFD codes and BEMT are in very good agreement. For the floating turbine, all predicted periodic profiles of rotor power and thrust are qualitatively similar, but the power peaks of both CFD predictions are significantly higher than those of BEMT. Moreover, cross-comparisons of the COSA and FLUENT predictions of blade static pressure also highlight significant compressible flow effects on rotor power and loads. The CFD analyses of the downstream rotor flow also reveal wake features unique to pitching turbines, primarily the space- and time-dependence of the wake generation strength, highlighted by intermittency of the tip vortex shedding.