Fundamental aerodynamics of the soccer ball
Fundamental aerodynamics of the soccer ball
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DOI：
10.1007/bf02844207
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发表时间：
2007-06-01
影响因子：
1.7
通讯作者：
Sakashita, R.
中科院分区：
文献类型：
--
作者：
Asai, T.;Seo, K.;Sakashita, R.
当运动球的边界层从层流转变为湍流时，会发生阻力危机，阻力系数（C-d）迅速下降。然而，足球的空气动力学特性和边界层动力学尚未得到很好的了解。在这项研究中，我们表明足球的临界雷诺数 (Re-crit) 范围为 2.2 x 10(5) 到 3.0 x 10(5)。风洞测试以及飞行中球的边界层动力学和尾涡的可视化表明，非旋转球和旋转（弯曲）球在超临界区域都具有较低的 C-d 值。此外，由于面板的影响，足球的 Re-crit 值低于光滑球体的 Re-crit 值，范围约为 3.5 x 10(5) 至 4.0 x 10(5)。这表明足球的空气动力学特性介于光滑球和高尔夫球之间。在流动可视化实验中，与亚临界状态相比，超临界状态下的分离点后退且 C-d 降低，这表明与在其他运动球中观察到的现象类似。对于一些不旋转和旋转的足球，尾流随着时间的推移而变化。一般来说，涡流的高频分量消散，而低频分量随着下游涡流的增加而增加。目前研究中观察到的涡流大规模波动的原因尚不清楚；然而，非旋转球的“指节球效应”可能在这一现象中发挥了作用。
When the boundary layer of a sports ball undergoes the transition from laminar to turbulent flow, a drag crisis occurs whereby the drag coefficient (C-d) rapidly decreases. However, the aerodynamic properties and boundary-layer dynamics of a soccer ball are not yet well understood. In this study we showed that the critical Reynolds number (Re-crit) of soccer balls ranged from 2.2 x 10(5) to 3.0 x 10(5). Wind-tunnel testing, along with visualisation of the dynamics of the boundary layer and the trailing vortex of a ball in flight, demonstrated that both non-spinning and spinning (curved) balls had low C-d values in the super-critical region. In addition, the Re-crit values of the soccer balls were lower than those of smooth spheres, ranging from similar to 3.5 x 10(5) to 4.0 x 10(5), due to the effects of their panels. This indicated that the aerodynamic properties of a soccer ball were intermediate between those of a smooth ball and a golf ball. In a flow visualisation experiment, the separation point retreated and the C-d decreased in a super-critical regime compared with those in a sub-critical regime, suggesting a phenomenon similar to that observed in other sports balls. With some non-spinning and spinning soccer balls, the wake varied over time. In general, the high-frequency component of an eddy dissipated, while the low-frequency component increased as the downstream vortex increased. The causes of the large-scale fluctuations in the vortex observed in the present study were unclear; however, it is possible that a 'knuckle-ball effect' of the non-rotating ball played a role in this phenomenon.