Breaking the Sound Barrier with an Aircraft

Military aircraft routinely accelerate to speeds greater than the local sound speed. Historically, this was referred to as "breaking the sound barrier". The passage from subsonic to supersonic speeds is accompanied by some unusual phenomena which lie in the realm of "nonlinear" mechanical events - events involving some degree of chaos.

军用飞机通常会加速至超过当地声速的速度。历史上，这种现象被称为“突破音障”。从亚音速到超音速的过渡伴随着一些异常现象，这些现象属于“非线性”机械事件的范畴——涉及一定程度的混沌。

One of the extraordinary sights associated with this supersonic transition is the production of a sudden visible vapor cloud around the aircraft. The report of the photographers is that they snap the shutter when they hear the sonic boom, which certainly associates the cloud with the breaking of the sound barrier. But the photo of the B-2 below, which is slightly subsonic, blurs that distinction. It seems safe to say that the phenomenon is associated with the extraordinary conditions very near the speed of sound. Mark Cramer describes this condensation effect in terms of the Prandtl-Glauert Singularity. In this phenomenon, the non-linear or "chaotic" effects amplify all pressure perturbations, leading to some regions of anomalously high and low pressure. If the associated volumes cannot quickly change, then the ideal gas law suggests that the temperature in the low pressure regions must drop, leading to condensation of the water vapor present. This general description probably applies, even though in the presence of condensation, the gases are not exactly "ideal".

与这一超音速过渡相关的非凡景象之一是飞机周围突然产生可见的蒸汽云。摄影师们报告说，他们在听到音爆时按下快门，这显然将云与突破音障联系在一起。但下面这张B-2飞机的图片略低于音速，却模糊了这种区别。似乎可以安全地说，这种现象与非常接近音速的特殊条件有关。Mark Cramer用Prandtl-Glauert奇点来描述这种凝结效应。在这种现象中，非线性或‘混沌’效应会放大所有压力扰动，导致某些区域出现异常高的和低的压力。如果相关体积不能迅速变化，那么根据理想气体定律，低压力区域的温度必须下降，从而导致存在水蒸气的凝结。这种一般描述可能适用，尽管在存在凝结的情况下，气体并不完全符合‘理想’气体的假设。

The photo credit is Photographer's Mate Airman Chris M. Valdez, Navy NewsStand -- Eye on the Fleet Photo Gallery ( http://www.news.navy.mil/view_photos.asp, 040129-N-0905V-024).

照片版权为摄影师士官查理斯·M·瓦尔德兹，海军新闻亭——《聚焦舰队》照片集（http://www.news.navy.mil/view_photos.asp，040129-N-0905V-024）。

This photo of the B-2 Spirit Stealth Bomber, which does not break the sound barrier, shows that the extraordinary cloud effect is not exactly tied to the breaking of the sound barrier. The aircraft was completing a mission over the Pacific Ocean.

这张B-2隐形轰炸机的照片显示，它并未突破音障，但其非凡的云层效应并不完全与突破音障有关。该飞机正在太平洋上空执行任务。

This photo is credited to Bobbi Garcia, a civilian aerial photographer working for Rohmann Services in support of the Air Force Flight Test Center (AFFTC). It appeared in the December 30, 2002 issue of Aviation Week and Space Technology.

这张照片归Bobbi Garcia所有，她是一名为Rohmann Services工作的民用航空摄影师，为空军飞行测试中心（AFFTC）提供支持。这张照片出现在2002年12月30日的《航空周与空间技术》（Aviation Week and Space Technology）期刊上。

2004年1月29日，太平洋海洋，美国海军第314海军陆战队攻击战斗机中队（VMFA-314）的美国战斗机，F14-B天雕战斗机，美国海军，地中海海区，2003年4月22日照片。照片说明：摄影师 Justin S. Osborne，海军新闻亭——《舰队之眼》照片集（http://www.news.navy.mil/view_photos.asp，030422-N-0382O-588）。F/A-18海 hornet 战斗机，美国海军，韩国釜山海岸，1999年7月7日照片。照片说明：Ensign John Gay，海军新闻亭——《舰队之眼》照片集（http://www.news.navy.mil/view_photos.asp，990707-N-6483G-001）。前三大照片及许多其他照片的参考文献：美国海军（USN，http://www.navy.mil），美国国防部（DoD，http://www.DefenseLink.mil 或 http://www.dod.gov），美国政府（USA）。