Flow speed has little impact on propulsive characteristics of oscillating foils
Flow speed has little impact on propulsive characteristics of oscillating foils
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DOI：
10.1103/physrevfluids.3.013103
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发表时间：
2017-07
期刊：
影响因子：
--
通讯作者：
T. Buren;D. Floryan;Nathaniel J. Wei;A. Smits
中科院分区：
文献类型：
--
作者：
T. Buren;D. Floryan;Nathaniel J. Wei;A. Smits
本文报道了二维翼型在水槽中作连续和间歇运动时的俯仰和垂荡性能实验。我们发现，推力和功率是独立的平均自由泳速度的两倍的变化的平均速度（四倍的动态压力），和振荡的速度高达38%的平均值，振荡的目的是模仿那些自由游泳运动的推力变化在扑动周期。我们证明了正确的速度尺度不是流动速度，而是后缘的平均速度。我们还发现流向速度变化对尾流特性（如涡流组织、涡流强度和时间平均速度剖面发展）的影响很小或没有影响--尾流在定性和定量上都没有变化。我们的研究结果表明，恒定速度的研究可以用来使强大的结论，而不需要探索自由游泳条件下的游泳性能。
Experiments are reported on the performance of a pitching and heaving two-dimensional foil in a water channel in either continuous or intermittent motion. We find that the thrust and power are independent of the mean freestream velocity for two-fold changes in the mean velocity (four-fold in the dynamic pressure), and for oscillations in the velocity up to 38\% of the mean, where the oscillations are intended to mimic those of freely swimming motions where the thrust varies during the flapping cycle. We demonstrate that the correct velocity scale is not the flow velocity but the mean velocity of the trailing edge. We also find little or no impact of streamwise velocity change on the wake characteristics such as vortex organization, vortex strength, and time-averaged velocity profile development---the wake is both qualitatively and quantitatively unchanged. Our results suggest that constant velocity studies can be used to make robust conclusions about swimming performance without a need to explore the free-swimming condition.