超疏水壁面湍流减阻特性及其对湍流拟序结构影响的TRPIV实验研究

Superhydrophobic surfaces has a broad application prospect in underwater drag reduction, pipeline transportation and so on. It is of great significance to study the mechanism and technology of turbulent drag reduction over superhydrophobic surfaces. In this proposal, the turbulent boundary layer flow fields over hierarchically structured surperhydrophobic surfaces with difference microstructures will be measured by Stereo-TRPIV and 2D-TRPIV techniques. By comparing with the hydrophilic surface, the following contents will be studied: 1) The drag reduction properties of hierarchically structured superhydrophobic surfaces with different microstructure will be analyzed. We will explore the relationship between the drag reduction and the parameters of the microstructure and then optimize the microstructures design. 2) Based on the idea of scale analysis and spatial topology, we will focus on the spatial topological morphology of turbulent coherent structures on superhydrophobic surfaces and its development and evolution rules in time and space. Based on the parameters of wall microstructure and slip length, a quantitative analysis on the turbulent coherent structure will be given. Then, we will summarize the drag reduction characteristics of the turbulent coherent structure and explore the effect of superhydrophobic surfaces on turbulent coherent structures, and the mechanism of its action. This investigation is not only helpful to reveal the turbulent drag reduction mechanism by superhyfrophobic surfaces, but also to provide some recommendations on wall microstructure design. Besides, to carry out this proposal will promote the development of turbulence theory and provide experimental basis for the turbulent coherent structure control in turbulent boundary layer , so it has important values on engineering application and academic research.

超疏水壁面在水下减阻、管道运输等方面具有广阔的应用前景，开展超疏水壁面湍流减阻机理及技术研究，具有重要意义。本项目拟综合利用Stereo-TRPIV和2D-TRPIV技术，对不同层级结构超疏水壁面上的湍流边界层流场进行实验测量，与亲水壁面对比，研究以下内容：1)不同层级结构超疏水壁面的减阻特性，探索其与壁面微观结构参数的关系，并进行优化设计；2)基于多尺度分析和空间拓扑的思想，研究超疏水湍流拟序结构的空间拓扑形态、及其在时间和空间上发展和演化的规律，结合壁面微观结构参数、滑移长度等对湍流拟序结构进行量化分析，并归纳减阻湍流拟序结构的特征，探索超疏水壁面对湍流拟序结构的影响及作用机理。本项目的开展不仅有利于揭示超疏水壁面湍流减阻机理、为超疏水壁面湍流减阻的工程应用提供壁面微观结构设计的建议，还有助于推进湍流理论的发展、为湍流边界层拟序结构控制提供实验依据，故具有重要的工程应用和学术研究价值。

超疏水壁面作为一种被动的水下减阻技术在船舶、潜艇、管道运输等方面具有重要的应用前景。同时，它也作为一种可调制壁湍流拟序结构的重要手段，成为研究湍流结构理论的一个重要途径。本项目围绕高减阻率超疏水壁面制备、超疏水壁面对湍流拟序结构影响及减阻机理、壁湍流拟序结构发展演化的动力学过程，展开了深入研究。本项目在执行过程中，制备了具有高减阻率沟槽超疏水壁面，从湍流统计量、湍流结构动力学及湍流结构统计方面为依据评估了超疏水壁面的减阻效果和减阻机理。在湍流结构研究方面，取得了3个重要成果，为对比研究超疏水壁面对壁湍流拟序结构的影响奠定了基础：通过合成射流锁相Stereo-PIV技术定量测量了三维发卡涡结构空间流场，并得到三维发卡涡诱导新发卡涡的三维演化过程；发展了移动TRPIV技术和超流场尺寸时空拓扑方法，实现了从拉格朗日框架下对湍流结构识别、定位、发展、演化、融合等的研究，并总结了湍流结构的迁移特性规律，促进了湍流结构理论与湍流统计理论的融合；由Tomo-PIV数据拓扑平均得到的三维发卡涡空间结构参数验证了早期提出的超疏水壁面发卡涡涡包模型。相关成果推动了对湍流结构的发展，也厘清了超疏水壁面减阻机理：超疏水壁面的滑移作用仅仅是减阻的前提，关键是在滑移的影响下制约了近壁拟序结构正常的发展演化过程，弱势的大尺度涡包结构难以承接外区大尺度结构通过剪切层对内区的能量传输过程，其自身发展缓慢也难以对壁面新兴结构形成强有力的调制，造成近壁喷射、扫掠活动减小、强度降低，进而实现减阻。本项目共发表期刊论文6篇，另有2篇SCI在投，相关科普工作获省级科学进步奖2等奖，获会议优秀论文奖1次。