2023-08-22 ブラウン大学
◆物体が水に触れると、水をはじく性質に関係なく、抵抗が増加し、特に物体が水中に完全に浸かる前に最大になります。部分的に水中にある物体の抵抗は、同じ材料でできた完全に浸かった物体の3〜4倍にもなることが示されました。また、水をはじく性質の高いコーティングが施された物体が、逆に他の物体よりも多くの抵抗を受けることも分かりました。
◆これらの発見は、空気と水の境界で動作する設計や構造に影響を与える可能性があり、部分的に水中にある物体に関する基本的な研究の重要性を強調しています。
＜関連情報＞
- https://www.brown.edu/news/2023-08-22/drag-sphere
- https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.8.084003
毛細管スケールでの部分水没球体の抗力 Drag on a partially immersed sphere at the capillary scale
Robert Hunt, Ze Zhao, Eli Silver, Jinhui Yan, Yuri Bazilevs, and Daniel M. Harris
Physical Review Fluids Published 22 August 2023
DOI:https://doi.org/10.1103/PhysRevFluids.8.084003
ABSTRACT
We study the drag on a centimetric sphere in a uniform flow in the presence of a free surface as a function of submergence depth. Through direct force measurements in a custom benchtop recirculating flume, we demonstrate that the drag can significantly exceed the corresponding drag in a single-phase flow and achieves a peak at submergence depths just prior to complete immersion. The additional drag in the partially immersed state is rationalized by considering hydrostatic effects associated with the asymmetric surface height profile induced by the obstacle in the flow direction which persists for flow speeds below the minimum capillary-gravity wave speed. At these scales, the sphere’s wettability plays a pronounced role in determining the maximum possible drag and results in hysteretic behaviors near touchdown and complete immersion. The influence of flow speed, sphere size, and surface tension on the drag characteristics are additionally explored through a combination of experiments and numerical simulations.
