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How to extract the angle attack on airfoils in cycloidal motion from a flow field solved with computational fluid dynamics? Development and verification of a robust computational procedure
Energy Conversion and Management ( IF 10.4 ) Pub Date : 2020-11-01 , DOI: 10.1016/j.enconman.2020.113284
Pier Francesco Melani , Francesco Balduzzi , Giovanni Ferrara , Alessandro Bianchini

Abstract One of the key problems faced by researchers dealing with Computational Fluid Dynamics simulations and rotating machines is represented by how to extract the angle attack from a numerically computed flow field. If this issue has been addressed successfully for some applications, in case of airfoils moving in cycloidal motion (i.e. having a rotational motion within a rectilinear flow field, like in Darrieus Vertical-Axis Wind Turbines) some proposals do exist, but always affected by some arbitrary choices on the velocity probing that are not supported by a proper verification. The aim of the present study is to try finding a robust computational procedure tailored for the scope. To this end, three different post-processing methods - detailed in the study – were considered and applied to the flow fields of 2-blade H-Darrieus rotor, coming from a high-fidelity unsteady model based on Computational Fluid Dynamics; the resulting blade angle of attack trends over one rotor revolution were then combined with available blade forces data to assess the corresponding lift and drag coefficients. In order to assess the actual accuracy of these approaches for a stable tip-speed ratio, the post-processed force coefficients were compared to the ones computed via a numerical pitching airfoil model, which received the sampled angle of attack trends as input; eventually, the pitched lift and drag values have been used to reconstruct the blade forces over one rotor revolution and compare them with the ones coming from full turbine simulations. Results show large scattering of obtained data, remarking the importance of the proper selection of the angle of attack sampling strategy for the analysis of turbine performance. Overall, the “LineAverage” approach, i.e. the use of multiple sampling points around the airfoil for velocity probing, has proved to be the most accurate method.

中文翻译:

如何从计算流体动力学求解的流场中提取摆线运动中翼型的角攻?稳健计算程序的开发和验证

摘要 处理计算流体动力学模拟和旋转机器的研究人员面临的关键问题之一是如何从数值计算的流场中提取角度攻击。如果此问题已在某些应用中成功解决,则在机翼以摆线运动(即在直线流场内具有旋转运动,例如在 Darrieus 垂直轴风力涡轮机中)的情况下,确实存在一些建议,但总是受到某些建议的影响适当验证不支持的速度探测的任意选择。本研究的目的是尝试找到适合该范围的稳健计算程序。为此,研究中详细介绍了三种不同的后处理方法,并将其应用于 2 叶片 H-Darrieus 转子的流场,来自基于计算流体动力学的高保真非定常模型;然后将转子旋转一圈内产生的叶片攻角趋势与可用的叶片力数据相结合,以评估相应的升力和阻力系数。为了评估这些方法对稳定叶尖速度比的实际精度,将后处理的力系数与通过数值俯仰翼型模型计算的系数进行比较,后者接收采样的迎角趋势作为输入;最终,俯仰升力和阻力值已被用于重建转子旋转一圈的叶片力,并将它们与来自完整涡轮机模拟的力进行比较。结果显示获得的数据分散很大,注意到正确选择攻角采样策略对涡轮机性能分析的重要性。总的来说,“LineAverage”方法,即在翼型周围使用多个采样点进行速度探测,已被证明是最准确的方法。
更新日期:2020-11-01
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