Experimental Study About The Flow Drag Reduction On Super-hydrophobic Surface At Macroscopic Level

For the application of super-hydrophobic surface about drag reduction, advanced flow experimental testing technology is used to study the drag-reducing mechanism and the drag reduction laws on various hydrophobic and super-hydrophobic surfaces fabricated by several kinds of methods at different flow patterns in this paper. This paper is under the support of NSFC(No. 50606025).The main contents are as follows:(1)Fabrication of super-hydrophobic surface and the study of wetting propertiesA variety of hydrophobic and super-hydrophobic surfaces with different surface structures and different wetting properties are fabricated by several kinds of methods. Video optical contact angle measuring instrument and scanning surface electron microscopy (SEM) are used to study the impact of surface structure on the static and dynamic wetting properties, which lays the foundation for further studying of the impact of hydrophobic characteristics on drag-reducing mechanism and laws.(2)PIV experimental study of the flow over micro-nano-structure super-hydrophobic surfacesIn an open low-speed circulating water tunnel, advanced particle image velocimetry technology is used to study the velocity profile near a variety of hydrophobic and super-hydrophobic wall surfaces prepared by the particles coating method and self-assembly method. A comparative study of the slip velocity and slip length, the near-wall velocity profile, the near-wall vorticity profile and the near-wall pulse at different flow patterns is carried out according to the PIV test results. It is found that: the different degrees of flow slip near the hydrophobic and super-hydrophobic surfaces has a significant impact on the near-wall vorticity and turbulence intensity, and the laws vary in different flow patterns.(3)Experimental study of the drag reduction for flow over the super-hydrophobic circular pipeA super-hydrophobic circular pipe flow resistance test bench is designed, built and calibrated. The law of drag reduction in laminar and turbulent flow over circular pipes with micro-nano-structured hydrophobic and super-hydrophobic wall is studied through the relationship between the pressure drop and flow rate. It is found that:?in laminar flow conditions, the drag reduction effect of the experimental hydrophobic and super-hydrophobic surface is not obvious. When the flow transits into the turbulent state, the circular pipe with hydrophobic wall and the circular pipe with super-hydrophobic wall will produce a more significant drag reduction effect, and with the Reynolds number increases, the drag reduction effect increased.