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Centrifugal Flows Drive Reverse Rotation of Feynman’s Sprinkler
Phys. Rev. Lett. 132, 044003 – Published 26 January, 2024
DOI: https://doi.org/10.1103/PhysRevLett.132.044003
Abstract
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.
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PRL Collection of the Year 2024
Here is our Collection of the Year 2024. We have gathered about one issue’s worth of Letters, representative of the wide range of interests of the communities advancing fundamental and applied physical science. We plan to have such a collection each year.
Focus
Feynman’s Reversed Sprinkler Puzzle Solved
Which direction would an S-shaped lawn sprinkler rotate if it were submerged and the flow were reversed? Experiments now provide a definitive answer.
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