世界杯足球在加州理工的風(fēng)洞測試

不同足球之間的主要區(qū)別之一是有多少氣流沿著球的表面流過。湍流將緊挨著球的曲面，從而減少足球的空氣阻力。在這個(gè)“普天同慶”（Jabulani）的高速視頻里，加州理工學(xué)院的科學(xué)家證明，空氣在經(jīng)過球的一半時(shí)就分離了。

(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）世界杯正在全面展開，新的足球正式命名為Jabulani，是祖魯語中“慶祝”的意思。 The players, however, aren't exactly celebrating. 但是，球員們似乎并未在慶祝。相反，他們很多都在抱怨球的軌跡難以預(yù)料，而且球本身難以控制，導(dǎo)致傳球失誤，射門打偏，守門員看起來像傻瓜一樣。那么究竟這個(gè)新的比賽用球是怎么挑起這些爭論的呢？

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.

為了找到答案，加州理工學(xué)院航空學(xué)助理教授貝弗利·麥凱恩（Beverley McKeon）實(shí)驗(yàn)室的工程師將一個(gè)“普天同慶”放入盧卡斯風(fēng)洞進(jìn)行測試。他們在那里的發(fā)現(xiàn)可能解釋“普天同慶”的不可預(yù)測性。

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，經(jīng)典黑白相間的足球，由32片五邊形和六邊形縫合而成，溝槽更深。而普天同慶，則由8個(gè)小片熱粘合在一起，紋路更淺，就像球體表面的微小浮雕似的。

深紋理的表面可能導(dǎo)致球周圍形成更多的湍流，麥克科恩解釋說，而湍流正是減少阻力使踢出去的球飛更遠(yuǎn)的因素（這就是為什么高爾夫球表面有酒窩狀的坑，以致你把精力都放在這項(xiàng)運(yùn)動上面）。當(dāng)球在空中速度減慢時(shí)，周圍的氣流從湍流變?yōu)榉€(wěn)定的層流。這個(gè)轉(zhuǎn)變細(xì)節(jié)上的差別很可能就是“普天同慶”和傳統(tǒng)足球不同的原因——換成球員的觀點(diǎn)就是：這球的行為變得不可預(yù)測。

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.

也有可能是風(fēng)、旋轉(zhuǎn)或其他方面影響對普天同慶的軌跡干擾更大。當(dāng)球在空中疾馳時(shí)，球表面變化多樣的氣流可以將它送往意料之外的路徑，讓許多足球運(yùn)動員驚愕不已。

        

媒體成員聚集在一起觀看測試。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.

不過，普天同慶并非古怪到球員無法學(xué)會控制它。“這就像球一旦有所改變，人們就需要花時(shí)間去適應(yīng)，”麥凱恩說。而且，從流體力學(xué)的角度來看，普天同慶也很有趣。研究足球周圍的氣流是麥凱恩課題的一個(gè)自然延伸——她和她的學(xué)生正在研究粗糙表面對氣流的影響，而足球課作為球體的測試模型。他們正在尋求僅通過改變表面紋理來控制氣流的方法。而他們所做的研究在飛行器設(shè)計(jì)中有很多應(yīng)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.

該團(tuán)隊(duì)這個(gè)夏天在麥凱恩實(shí)驗(yàn)室進(jìn)行研究，成員包括博士后米歇爾·瓜拉（Michele Guala），研究生伊恩·雅可比（Ian Jacobi）和梅麗莎·克里斯滕森（Melissa Christensen）以及加州大學(xué)圣地亞哥分校的本科生。

Provided by California Institute of Technology

由加州理工學(xué)院提供