Effects of hydrophobicity-induced wall slip on turbulence drag and turbulence structure

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)提供资金的。CBET-0853657 Papavassiliou，Dimitrios V.这个项目将研究可能导致固-液界面流体滑移的基本分子机制，以及流体滑移如何确切地影响远离粘性壁子层的湍流结构。最近有文献证明，超疏水表面会导致流体在其上滑动。对于层流流动，壁面的这种滑移导致了已经在实验和计算中观察到的减阻。最近的计算工作表明，只有当超疏水表面在壁面产生显著的流体滑移时，它们才能导致湍流减阻。湍流减阻是通过引入非常少量的添加剂，如聚合物、表面活性剂或微泡来实现的。这些方法主要适用于内部流动。然而，当流体在物体周围流动时，使用添加剂来改变流体属性充其量也是不切实际的。如果对管道(或车辆)表面进行超疏水处理可以减少阻力，那么这种处理将提供一种既适用于内部流动又适用于外部流动的减阻技术。本文主要研究了固液界面上流体滑移产生的条件，以及这种滑移对湍流减阻的影响。需要研究的具体问题包括：疏水性与流体滑移之间的关系及其基于固体-流体界面附近流体的分子结构的解释；探索可能导致流体滑移的流体类型和界面类型；以及确定滑移影响湍流产生和维持的机制。这些发现将对固体表面附近的流体流动理论和湍流理论以及许多工业应用具有重要意义。这项研究项目的各个方面将有助于开发一门新课程，并将纳入现有课程。此外，通过该项目生成的数据库将通过现有的网络服务器提供给社区，并规划可作为验证基准的数据库。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). CBET -0853657 Papavassiliou, Dimitrios V.This project will investigate the fundamental molecular mechanisms that can result in fluid slip at a solid-fluid interface and how exactly, if at all, fluid slip affects the structure of turbulence away from the viscous wall sublayer. It has been recently documented that ultra-hydrophobic surfaces induce slip in fluids moving over them. For laminar flows, this slip at the wall results in drag reduction that has been observed both experimentally and computationally. Recent computational work shows that ultra-hydrophobic surfaces can lead to turbulent drag reduction only when they result in significant fluid slip at the wall. Turbulent drag reduction has been achieved with the introduction of a very small amount of additives, such as polymers, surfactants or microbubbles. Such methods are mainly feasible for internal flows. However, when a fluid flows around an object, the use of additives to alter the fluid properties is at best impractical. If treating a conduit (or a vehicle) surface such that it becomes ultra-hydrophobic can result in drag reduction, then such treatment will present a drag-reduction technology feasible for both internal and external flows. This study is focused on the fundamental investigation of the conditions that generate fluid slip at the solid-water interface, and the effects that such slip can have on turbulence drag reduction. Specific issues to be investigated include the correlation between hydrophobicity and fluid slip and its interpretation based on the molecular structure of the fluid next to a solid-fluid interface, the exploration of the type of fluid and the type of interface that can result in fluid slip, and the determination of the mechanism by which slip affects the generation and maintenance of turbulence. These findings will be significant for the theory of fluid flow next to solid surfaces and for turbulence, as well as for many industrial applications. Aspects of this research project will be instrumental in the development of a new course and will be integrated in existing courses. In addition, the database generated through this project will become available to the community through existing web servers, and databases that can serve as validation benchmarks are planned.