2024-01-26 ニューヨーク大学 (NYU)
◆逆スプリンクラーは水を吸い込むときも水を噴出するときと同じ方向に回転し、その原因は微妙で驚くべきものであることがわかりました。この研究により、流体力学の物理学における最も古く難しい問題の一つが解決され、逆スプリンクラーの動作を理解することには控えめな実用性があるとしつつも、流体の流れを制御するための装置の設計において有益な情報が得られました。
＜関連情報＞
- https://www.nyu.edu/about/news-publications/news/2024/january/how-does-a–reverse-sprinkler–work–researchers-solve-decades-o.html
- https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.044003
遠心流がファインマンのスプリンクラーを逆回転させる Centrifugal Flows Drive Reverse Rotation of Feynman’s Sprinkler
Kaizhe Wang, Brennan Sprinkle, Mingxuan Zuo, and Leif Ristroph
Physical Review Letters 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.
