再论喷水头：马赫推进中的动量、力和流
Sprinkler Head Revisited: Momentum, Forces, and Flows in Machian Propulsion
摘要：
从1883年恩斯特·马赫开始，许多实验者都报告说，如果一个装置交替地吸入和排出周围的流体，那么它的运动方向就好像只是排出流体一样。这种令人惊讶的现象，我们称之为“马赫推进”，可以用动量守恒来解释：流出物有效地将动量从设备转移到周围介质中，而流入物只能通过粘性扩散来实现。然而，以前的许多理论讨论都集中在流出和流入形状的差异上。基于守恒的论证是直接而完整的，而对流动形状的分析则更为微妙，首先需要守恒。我们的讨论涵盖了三种通常被分开处理的设备：反向喷头（也称为反向喷头或费曼喷头），推杆-推杆船和吸气悬臂。然后，我们简要地提到一些应用马赫推进，从微型工程到天体物理学。
英文摘要：
Many experimenters, starting with Ernst Mach in 1883, have reported that if a device alternately sucks in and then expels a surrounding fluid, it moves in the same direction as if it only expelled fluid. This surprising phenomenon, which we call "Machian propulsion," is explained by conservation of momentum: the outflow efficiently transfers momentum away from the device and into the surrounding medium, while the inflow can do so only by viscous diffusion. However, many previous theoretical discussions have focused instead on the difference in the shapes of the outflow and the inflow. Whereas the argument based on conservation is straightforward and complete, the analysis of the shapes of the flows is more subtle and requires conservation in the first place. Our discussion covers three devices that have usually been treated separately: the reverse sprinkler (also called the inverse, or Feynman sprinkler), the putt-putt boat, and the aspirating cantilever. We then briefly mention some applications of Machian propulsion, ranging from microengineering to astrophysics.
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