Science Alert February 6, 2024
The issue of reversibility in hydromechanical sprinklers that auto-rotate while ejecting fluid from S-shaped tubes raises fundamental questions that remain unresolved. Through experiments a team of researchers in the US (New York University, Colorado School of Mines) has shown robust and persistent reverse rotation under suction and developed a model that accounted for the observed motions. They implemented an apparatus that allowed for free rotation under ejection and suction for a range of flow rates and arbitrarily long times. Flow measurements revealed a rocketlike mechanism shared by the reverse and forward modes that involved angular momentum flux whose subtle manifestation in the reverse case stems from centrifugal effects for flows in curved conduits. According to the researchers their findings answer Feynman’s long-standing question by providing quantitatively accurate explanations of both modes, and they suggested further inquiries into flux-based force generation and the roles of geometry and Reynolds number… read more. TECHNICAL ARTICLE
Experimental setup. Credit: Phys. Rev. Lett. 132, 044003, 26 January 2024