This paper provides a fundamental understanding of the unsteady fluid-dynamic phenomena on a cycloidal rotor blade operating at ultra-low Reynolds numbers (Re ∼ 18,000) by utilizing a combination of instantaneous blade force and flowfield measurements. The dynamic blade force coefficients were almost double the static ones, indicating the role of dynamic stall. For the dynamic case, the blade lift monotonically increased up to ±45° pitch amplitude; however, for the static case, the flow separated from the leading edge after around 15° with a large laminar separation bubble. There was significant asymmetry in the lift and drag coefficients between the upper and lower halves of the trajectory due to the flow curvature effects (virtual camber). The particle image velocimetry measured flowfield showed the dynamic stall process during the upper half to be significantly different from the lower half because of the reversal of dynamic virtual camber. Even at such low Reynolds numbers, the pressure forces, as opposed to viscous forces, were found to be dominant on the cyclorotor blade. The power required for rotation (rather than pitching power) dominated the total blade power.

中文翻译：

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力和流场测量以了解在超低雷诺数下悬停的摆线转子的非定常空气动力学

本文通过结合瞬时叶片力和流场测量，提供了对以超低雷诺数（Re ∼ 18,000）运行的摆线转子叶片上的非定常流体动力学现象的基本理解。动态叶片力系数几乎是静态力系数的两倍，表明动态失速的作用。对于动态情况，叶片升力单调增加至±45°俯仰幅度；然而，对于静态情况，流动在大约 15° 后与前缘分离，并带有大的层流分离气泡。由于流动曲率效应（虚拟弯度），轨迹的上半部分和下半部分之间的升力和阻力系数存在显着的不对称性。粒子图像测速测量流场表明，由于动态虚拟弯度的反转，上半部分的动态失速过程与下半部分有显着差异。即使在如此低的雷诺数下，与粘性力相反，压力在旋转转子叶片上仍占主导地位。旋转所需的功率（而不是俯仰功率）主导了叶片的总功率。