Department of Mechanical Engineering, University of Alberta, Edmonton, AB, T6G 1H9, Canada.
Sci Rep. 2017 Jan 27;7:41448. doi: 10.1038/srep41448.
Among diverse methods for drag reduction, superhydrophobicity has shown considerable promise because it can produce a shear-free boundary without energy input. However, the plastron experiences a limited lifetime due to the dissolution of trapped air from surface cavities, into the surrounding water. The underwater longevity of the plastron, as it is influenced by environmental conditions, such as fine particles suspended in the water, must be studied in order to implement superhydrophobicity in practical applications. We present a proof-of-concept study on the kinetics of air loss from a plastron subjected to a canonical laminar boundary layer at Re = 1400 and 1800 (based on boundary layer thickness) with and without suspending 2 micron particles with density of 4 Kg/m. To monitor the air loss kinetics, we developed an in situ non-invasive optical technique based on total internal reflection at the air-water interface. The shear flow at the wall is characterized by high resolution particle image velocimetry technique. Our results demonstrate that the flow-induced particle-plastron collision shortens the lifetime of the plastron by ~50%. The underlying physics are discussed and a theoretical analysis is conducted to further characterize the mass transfer mechanisms.
在各种减阻方法中，超疏水性因其可以在无需能量输入的情况下产生无剪切边界而显示出巨大的潜力。然而，由于表面微腔中被困空气的溶解，水的润湿性会受到限制，从而限制了水翼的水下寿命。为了在实际应用中实现超疏水性，必须研究环境条件（如水中悬浮的细小颗粒）对水翼润湿性的影响。我们进行了一项概念验证研究，研究了在 Re=1400 和 1800（基于边界层厚度）条件下，有和没有悬浮 2 微米颗粒（密度为 4kg/m³）的情况下，经典层流边界层中空气从水翼损失的动力学。为了监测空气损失动力学，我们开发了一种基于空气-水界面全内反射的原位非侵入式光学技术。通过高分辨率粒子图像测速技术来测量壁面剪切流。我们的结果表明，流动诱导的颗粒-水翼碰撞将水翼的寿命缩短了约 50%。讨论了潜在的物理机制，并进行了理论分析以进一步表征传质机制。
