Oscillating pendulum decay by emission of vortex rings.
Oscillating pendulum decay by emission of vortex rings.
复制标题
振荡摆因涡环的发射而衰减。
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
R. Donnelly
中科院分区：
文献类型：
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作者：
D. Bolster;Robert E. Hershberger;R. Donnelly
本文用球形物体研究了水中单摆的振动。通过测量势能的损失，我们估计了球体上的阻力系数，并与液氦实验的数据进行了比较。阻力系数比较非常有利地说明了这种现象的真实缩放行为。我们还研究了摆的振幅随时间的衰减。如前所述，在小振幅下，摆锤上的阻力由线性斯托克斯阻力给出，并且衰减是指数的。对于较大的振幅，摆锤在反转方向时会脱落涡环。传递给这些涡环的动量在摆锤上产生额外的离散阻力。我们目前的实验和理论估计，这种涡环诱导阻力。我们解析推导出一个临界振幅超过涡环脱落将发生，以及作为振幅的函数的环的半径的估计的估计。
We have studied oscillation of a pendulum in water using spherical bobs. By measuring the loss in potential energy, we estimate the drag coefficient on the sphere and compare to data from liquid-helium experiments. The drag coefficients compare very favorably illustrating the true scaling behavior of this phenomenon. We also studied the decay of amplitude of the pendulum over time. As observed previously, at small amplitudes, the drag on the bob is given by the linear Stokes drag and the decay is exponential. For larger amplitudes, the pendulum bob sheds vortex rings as it reverses direction. The momentum imparted to these vortex rings results in an additional discrete drag on the bob. We present experiments and a theoretical estimate of this vortex-ring-induced drag. We analytically derive an estimate for a critical amplitude beyond which vortex ring shedding will occur as well as an estimate of the radius of the ring as a function of amplitude.