Yuehao Luo

Superhydrophobic surface has potential drag reduction effect on both laminar and turbulent flowing stations, and it has increasingly come into the picture throughout the world. Superhydrophobicity is not only determined by the chemical properties on the interfaces, but also the hierarchical nano/microstructure on the contact surface. In this paper, the precise cutting method in turning machine is explored and exploited to fabricate the microgrooved surfaces. The wetting experiments illustrate that as the size of microgrooves becomes smaller, the water repellent property is improved progressively. In addition, the hydrodynamic experiments in a water tunnel show that friction force is decreased >8% with a smooth skin as baseline. The results in this research would expand the applications of bioinspired surfaces in fluid engineering.

With the rapid development of science and technology, increasing research interests have been focused on environment protection, global warming, and energy shortage. At present, reducing friction force as much as possible has developed into an urgent issue. Sharkskin effect has the potential ability to lower viscous drag on the fluid-solid interface in turbulence, and therefore, how to fabricate bio-inspired sharkskin surfaces is progressively becoming the hot topic. In this review, various methods of fabricating drag reduction surfaces covering biological sharkskin morphology are illustrated and discussed systematically, mainly involving direct bio-replicated, synthetic fabricating, bio/micro-rolling, enlarged solvent-swelling, drag reduction additive low-releasing, trans-scale enlarged three-dimensional fabricating, flexible printing, large-proportional shrunken bio-replicating, ultraviolet (UV) curable painting, and stretching deformed methods. The overview has the potential benefits in better acquainting with the recent research status of fabricating sharkskin surfaces covering the biological morphology.

Nano/micro-imprinting technology base on polymer material coating has attracted the increasing attentions throughout the world in the past several decades, and it is progressively developing into the hot topic at present, in which, how to improve the manufacturing efficiency is becoming the urgent issue to be resolved. Polymer?s curing process is exactly complicated and sophisticated, which involves simultaneously performing physical and chemical changes, when the curing reaction reaches certain level, the system will abruptly transform into insoluble, non-melting gel with rapidly increased viscosity and rigidity, which can generate fixed deformation under persistent external pressure. In this paper, the plastic deformation capacity of epoxy resin in the curing process is investigated by the micro-dimple imprinting experiment, and the relationship between forming precision and curing degree is ascertained adopting the DSC (differential scanning calorimetry) method. In addition, the instantaneous micro-imprinting technology based on the micro-grooves is explored, and the experimental results indicate that the forming precision can surpass 90%. The paper will establish a novel avenue to apply the nano/micro imprinting technology into practical engineering.

Sharkskin effect is progressively coming into the picture in recent several decades, especially focusing on its drag reduction effect in turbulence. The up‐to‐date research in this article reveals the anisotropic wetting and fluidic phenomena on different sharkskin surfaces. Firstly, the contact angle model based on anisotropic pattern is established. Secondly, the anisotropic wetting and fluidic properties are investigated, and the experimental results can define the relationship between wetting parameters and stretching ratio, and in addition, the anisotropic model is validated. Finally, the possible hypotheses elucidating the wetting model and experiment results are put forward.

Shark is the fast swimming animal in the ocean, and it is well-known for sharkskin effect. Sharkskin is covered by the tiny and rigid scales, which can stick out of the viscous sublayer and effectively inhibit the occurrence of turbulence and reduce the wall resistance. The longitudinal sections of the scale surface are not parallel to the flowing direction, but at a particular attack angle, which could be considered as a supplement to the mechanism of sharkskin effect. At present, it is almost impossible to observe the variation of scales’ attack angles during the biological shark's swimming. Although the real sharkskin surfaces with original sizes have been fabricated by the bio-replicated method, the attack angles cannot be exactly controlled, the result of which is that the drag-reducing efficiency of sharkskin with different attack angles cannot be obtained by the experimental methods. In this paper, the highly accurate three dimensional digital model is exactly built through the high-accurate scanning the biological sharkskin, and the micro flow field is investigated comprehensively and deeply, especially that, the influence of scales’ attack angles on drag-reducing efficiency is analyzed, which has the important significance on exploring the sharkskin effect.

Energy conservation and environmental protection has progressively developed into the hot and popular topics in nowadays. In the process of natural gas transmission, almost all the power of the compressor stations has been used to overcome the friction consumption between the flowing gas and pipeline wall, so large numbers of resources are spent on the maintenance of the pumping stations every year. How to reduce the wall friction and increase the transportation output has been becoming the urgent problem to be resolved. Internal smooth coating, injecting nano-chain drag reduction agent and bio-inspired drag-reducing morphology have been gradually taken into application in the past several decades, and the field testing results were all striking and satisfactory. An overview of applying different drag reduction technologies into nature gas pipelining is systemically presented in detail, which has the important significance to understand research status and development tendency of nature gas industry.