Significant and stable drag reduction with air rings confined by alternated superhydrophobic and hydrophilic strips

Hu, Haibao and Wen, Jun and Bao, Luyao and Jia, Laibing and Song, Dong and Song, Baowei and Pan, Guang and Scaraggi, Michele and Dini, Daniele and Xue, Qunji and Zhou, Feng (2017) Significant and stable drag reduction with air rings confined by alternated superhydrophobic and hydrophilic strips. Science Advances, 3 (9). e1603288. ISSN 2375-2548

[img]
Preview
Text (Hu-etal-SA2017-Significant-and-stable-drag-reduction-with-air-rings-confined)
Hu_etal_SA2017_Significant_and_stable_drag_reduction_with_air_rings_confined.pdf
Final Published Version
License: Creative Commons Attribution 4.0 logo

Download (2MB)| Preview

    Abstract

    Superhydrophobic surfaces have the potential to reduce the viscous drag of liquids by significantly decreasing friction at a solid-liquid interface due to the formation of air layers between solid walls and interacting liquids. However, the trapped air usually becomes unstable due to the finite nature of the domain over which it forms. We demonstrate for the first time that a large surface energy barrier can be formed to strongly pin the three-phase contact line of air/water/solid by covering the inner rotor of a Taylor-Couette flow apparatus with alternating superhydrophobic and hydrophilic circumferential strips. This prevents the disruption of the air layer, which forms stable and continuous air rings. The drag reduction measured at the inner rotor could be as much as 77.2%. Moreover, the air layers not only significantly reduce the strength of Taylor vortexes but also influence the number and position of the Taylor vortex pairs. This has strong implications in terms of energy efficiency maximization for marine applications and reduction of drag losses in, for example, fluid transport in pipelines and carriers.