Centrifugal Flows Drive Reverse Rotation of Feynman's Sprinkler.

Centrifugal Flows Drive Reverse Rotation of Feynman's Sprinkler.

The issue of reversibility in hydromechanical sprinklers that auto-rotate while ejecting fluid from S-shaped tubes raises fundamental questions that remain unresolved. Here, we report on precision experiments that reveal robust and persistent reverse rotation under suction and a model that accounts for the observed motions. We implement an ultralow friction bearing in an apparatus that allows for free rotation under ejection and suction for a range of flow rates and arbitrarily long times. Flow measurements reveal a rocketlike mechanism shared by the reverse and forward modes that involves angular momentum flux, whose subtle manifestation in the reverse case stems from centrifugal effects for flows in curved conduits. These findings answer Feynman's long-standing question by providing quantitatively accurate explanations of both modes, and they suggest further inquiries into flux-based force generation and the roles of geometry and Reynolds number.

从S形管喷射流体时自动旋转的水力机械喷头的可逆性问题引发了一些尚未解决的基本问题。在此，我们报道了精确的实验，这些实验揭示了在吸力作用下强劲且持续的反向旋转，以及一个能解释所观察到的运动的模型。我们在一种装置中采用了一种超低摩擦轴承，该装置能在一系列流量以及任意长的时间内，在喷射和吸力作用下实现自由旋转。流量测量揭示了一种类似于火箭的机制，正向和反向模式都存在这种机制，它涉及角动量通量，其在反向情况下的微妙表现源于弯曲管道中流动的离心效应。这些发现通过对两种模式提供定量准确的解释，回答了费曼长期存在的问题，并且它们为进一步探究基于通量的力的产生以及几何形状和雷诺数的作用提供了思路。