世界杯足球在加州理工的风洞测试

不同足球之间的主要区别之一是有多少气流沿着球的表面流过。湍流将紧挨着球的曲面，从而减少足球的空气阻力。在这个“普天同庆”（Jabulani）的高速视频里，加州理工学院的科学家证明，空气在经过球的一半时就分离了。

(PhysOrg.com) -- The World Cup is in full swing, complete with an official new soccer ball named Jabulani, meaning "to celebrate" in Zulu. The players, however, aren't exactly celebrating. Instead, many of them are complaining that the ball's trajectory is too hard to predict, and that the ball itself is too hard to control, resulting in wayward passes, shots flying off target, and goalkeepers looking silly. So what exactly is it about the new ball that's provoking all the controversy?

（PhysOrg.com）世界杯正在全面展开，新的足球正式命名为Jabulani，是祖鲁语中“庆祝”的意思。 The players, however, aren't exactly celebrating. 但是，球员们似乎并未在庆祝。相反，他们很多都在抱怨球的轨迹难以预料，而且球本身难以控制，导致传球失误，射门打偏，守门员看起来像傻瓜一样。那么究竟这个新的比赛用球是怎么挑起这些争论的呢？

To find out, Caltech engineers in the lab of Assistant Professor of Aeronautics Beverley McKeon put an official Jabulani through its paces in the Lucas Adaptive Wall Wind Tunnel. And what they found there may explain the seemingly unpredictable nature of the Jabulani.

为了找到答案，加州理工学院航空学助理教授贝弗利·麦凯恩（Beverley McKeon）实验室的工程师将一个“普天同庆”放入卢卡斯风洞进行测试。他们在那里的发现可能解释“普天同庆”的不可预测性。

To start with, the classic black and white soccer ball, stitched together from 32 panels of pentagons and hexagons, has deeper grooves. The Jabulani, which is made from only eight panels thermally bonded together, has more shallow grooves, as well as tiny raised patterns along its surface.

首先，经典黑白相间的足球，由32片五边形和六边形缝合而成，沟槽更深。而普天同庆，则由8个小片热粘合在一起，纹路更浅，就像球体表面的微小浮雕似的。

深纹理的表面可能导致球周围形成更多的湍流，麦克科恩解释说，而湍流正是减少阻力使踢出去的球飞更远的因素（这就是为什么高尔夫球表面有酒窝状的坑，以致你把精力都放在这项运动上面）。当球在空中速度减慢时，周围的气流从湍流变为稳定的层流。这个转变细节上的差别很可能就是“普天同庆”和传统足球不同的原因——换成球员的观点就是：这球的行为变得不可预测。

It's also possible that wind, spin, or other influences can have a stronger effect on the Jabulani's trajectory. As the ball hurtles through the air, the varying air flow around it can send it on unexpected paths, to the consternation of many soccer players.

也有可能是风、旋转或其他方面影响对普天同庆的轨迹干扰更大。当球在空中疾驰时，球表面变化多样的气流可以将它送往意料之外的路径，让许多足球运动员惊愕不已。

        

媒体成员聚集在一起观看测试。Credit: Jenny Somerville

Still, the Jabulani isn't so unpredictable that players can't learn to control it. "It seems like anytime the ball is changed, it takes a while for people to adapt," McKeon says. And from a fluid mechanics standpoint, the Jabulani's also pretty interesting. Studying the air flow around soccer balls is a natural extension of McKeon's research, in which she and her colleagues study how surface roughness affects air flow, using spheres as test models. They're looking at how they can control air flow just by changing the texture of a surface. Their work has many applications in aircraft design, for example.

不过，普天同庆并非古怪到球员无法学会控制它。“这就像球一旦有所改变，人们就需要花时间去适应，”麦凯恩说。而且，从流体力学的角度来看，普天同庆也很有趣。研究足球周围的气流是麦凯恩课题的一个自然延伸——她和她的学生正在研究粗糙表面对气流的影响，而足球课作为球体的测试模型。他们正在寻求仅通过改变表面纹理来控制气流的方法。而他们所做的研究在飞行器设计中有很多应用。

The team that conducted the test includes postdoc Michele Guala, graduate student Ian Jacobi, and Melissa Christensen, an undergraduate from UC San Diego working in McKeon's lab this summer.

该团队这个夏天在麦凯恩实验室进行研究，成员包括博士后米歇尔·瓜拉（Michele Guala），研究生伊恩·雅可比（Ian Jacobi）和梅丽莎·克里斯滕森（Melissa Christensen）以及加州大学圣地亚哥分校的本科生。

Provided by California Institute of Technology

由加州理工学院提供