Design, Fabrication, and Evaluation of Superhydrophobic (SHPo) Surfaces for Drag Reduction in Turbulent Boundary Layer Flows
Design, Fabrication, and Evaluation of Superhydrophobic (SHPo) Surfaces for Drag Reduction in Turbulent Boundary Layer Flows
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用于减少湍流边界层流阻力的超疏水 (SHPo) 表面的设计、制造和评估
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发表时间：
2016
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通讯作者：
Muchen Xu
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作者：
Muchen Xu
Author（s）：徐，慕晨|顾问：Kim，Chang-Jin|摘要：在液体超疏水（SHPo）表面上维持一个气体层，由于在许多流动应用中减少摩擦阻力的可能性，引起了人们的极大关注。虽然许多SHPo表面被证明可以显著降低阻力（例如，g 10%），并且某些SHPo表面被证明具有空前大的滑移长度（例如，g 100微米），但是在反映大多数应用（例如海洋环境中的船只）的湍流中，显著的阻力减小仍然是难以实现的。认识到气体层（称为胸甲）的关键，并研究其鲁棒性在不同深度的水下，我们首先得出结论，SHPo表面能够显着减阻不能无限期地保持胸甲，如果浸没在几厘米深。通过开发一种用于厘米大小样品表面的高分辨率剪切传感器，并使用硅SHPo表面，使胸甲比其他表面更坚固，我们在雷诺数高达1.1x107的湍流边界层流动中获得了高达25%的减阻。在高速水洞和高速拖曳水槽中获得的结果还表明，阻力随着雷诺数的增加而减少，这证实了文献中的数值研究。此外，我们开发并进行SHPo阻力实验，首次在海洋条件下使用真实的船，实现约20%的阻力减少。最后，一个可扩展的制造过程中开发的无源和半有源SHPo表面的放大制造。对于半主动SHPo表面，即，SHPo表面具有自调节气体恢复能力，我们提出并证明了一种气体生成机制，不需要任何外部电源输入。
Author(s): Xu, Muchen | Advisor(s): Kim, Chang-Jin | Abstract: Sustaining a gas layer on them in liquid, superhydrophobic (SHPo) surfaces have attracted enormous attention due to the possibility of reducing friction drag in numerous flow applications. Although many SHPo surfaces proved to reduce drag significantly (e.g., g 10%) in microchannel flows and certain SHPo surfaces proved to have an unprecedentedly large slip length (e.g., g 100 microns), a significant drag reduction is still elusive in turbulent flows that reflect most applications, such as watercraft in marine environment. Recognizing the gas layer (called plastron) as the key and studying its robustness under water of varying depths, we first conclude that the SHPo surfaces capable of a significant drag reduction cannot maintain the plastron indefinitely if submerged deeper than a few centimeters. By developing a high-resolution shear sensor for centimeters-size sample surfaces and using silicon SHPo surfaces that keep plastron more robust than others, we obtain up to ~25% drag reduction in turbulent boundary layer flows at Reynolds numbers up to 1.1x107. Obtained at a high-speed water tunnel and a high-speed tow tank, the results also indicate that the drag reduces more with increasing Reynolds number, corroborating the numerical studies in the literature. Moreover, we develop and conduct SHPo drag experiments using a real boat in marine conditions for the first time, achieving ~20% drag reduction. Finally, a scalable fabrication process is developed for scale-up manufacturing of both passive and semi-active SHPo surfaces. For the semi-active SHPo surfaces, i.e., SHPo surfaces with self-regulating gas restoration capability, we propose and demonstrate a gas generation mechanism that does not require any external power input.