【作者】 孙鹏翔；

【导师】 王敏杰； 赵丹阳；

【作者基本信息】 大连理工大学 ， 机械制造及其自动化， 2010， 硕士

【摘要】 随着能源危机的蔓延,减阻技术发展成为世界各国科学技术竞争的重要内容之一目前有多种减阻方法,但这些方法都存在有一定的局限性。生物形体为人类提供了丰富的构形资源。通过流体动力学和湍流研究水平的不断深入,人们发现物体表面如果有一定形状的沟槽,减阻效果将会更好。其中以“鲨鱼皮效应”著称的鲨鱼为人类提供了完美的减阻模板。人们已经通过对鲨鱼鳞盾沟槽模型进行放大和简化制造出了仿生鲨鱼皮。人工仿生鲨鱼皮在航空航天、远洋海运、石油管道运输等方面具有重要的应用前景,但成型出与真实鲨鱼皮微观形貌相近的仿生鲨鱼皮仍是尚未解决的难题。首先,本文对鲨鱼皮表面鳞盾沟槽结构的减阻机理进行了研究。采用有限元流体动力学软件Fluent进行数值计算。本文将计算模型简化并将整个计算分为沟槽减阻机理和鳞盾结构减阻机理两部分。计算结果表明：沟槽内部二次涡的对流作用是沟槽减阻的主要原因。鲨鱼皮表面减阻效果较好的另一个原因是鳞盾间的空隙中充满低速安静的流体,在空隙的顶端存在微小“涡旋”,这些“涡旋”可以起到将滑动摩擦变为滚动摩擦,并且阻止鳞片外部的高速流体进入鳞片内部空间的作用。然后,本文针对鲨鱼皮表面特有的鳞盾沟槽结构提出了热压电铸法和真空浇注法两种复制方法。热压电铸法是指利用高分子材料在鲨鱼皮样本上通过加热施压的方法复制鲨鱼皮表面特有的鳞盾沟槽结构,然后以此为电铸原型进行电铸最终得到鲨鱼皮金属模具的方法。真空浇注法是指向鲨鱼皮样本表面浇注液态复制材料,然后利用真空设备去除复制材料中的气泡,在固化剂的化学反应作用下,复制材料凝固,然后脱模得到鲨鱼皮复制品的方法。通过对这两种方法进行观察和对比得知,鲨鱼皮金属电铸模具表面鳞盾沟槽结构基本上被复制了下来,微沟槽清晰,鳞盾结构层次分明。真空浇注法得到的鲨鱼皮复制模板表面的鳞盾层次分明,鳞盾表面微沟槽轮廓完整、清晰,与真实鲨鱼皮相似度较高。但是鲨鱼皮金属电铸模具表面圆角现象比较严重,这种现象与电铸原型的复杂形状有关。因此从结果上来看,真空浇注法是一种相对较为理想的鲨鱼皮复制方法。更多还原

【Abstract】 With the spreading of energy crisis, drag reduction technology has been an important part of science and technology competition between countries. There are several drag reduction methods which have been taken into practice, however all these methods have limitation in application. Natural creatures provide rich knowledge resource to help human beings to solve engineering problems, such as "shark skin effect" which provides human being with a perfect drag reduction template. With the development of hydrodynamics and turbulence researching, it was fount out that a certain shape of groove on surface could help to reduce drag. Shark skin replica had been produced through amplification and simplification. Artificial shark skin replica would be widely applied in aerospace, ocean shipping, oil pipeline. However, the production of replica which has the similar riblet and scale structure with real shark skin is still a problem.Firstly, drag reduction mechanism of shark riblet was studied by numerical analysis. Fluent software was applied in numerical simulation. Because of the difficulty of creating a similar 3D shark skin computing modeling, two parts of the drag reduction numerical simulation of shark skin, riblet drag reduction numerical simulation and scale drag reduction numerical simulation, were researched separately. The results indicated that the convection movement of secondary vortex is the main reason of riblet drag reduction. Another reason of riblet drag reduction is the existence of small space between the scales which can hold low speed fluid. The small vortex in the space can turn sliding friction into rolling friction and prevent high speed fluid rushing the wall of shark skin scale.Then, two methods, heat-embossing electroforming method and vacuum casting method were attampted in shark skin replicating. Process of heat-embossing electroforming method includes three steps:Firstly, micro-replication template was produced with PMMA by heat-embossing. Then, PE shark skin replica was produced by polymer casting based on shark skin template. Finally, taking the PE replica as an electroforming template, the shark skin nickel mould was finished after electroforming. Process of vacuum casting method includes two steps:Firstly, replication material was casted onto shark skin and put into vacuum tank. After solidification, the mould was finished. Then, liquid silicone rubber shark skin replica was produced by using of this mould in vacuum environment also. It could be concluded as following after comparison and analysis. Clear and similar shark skin riblet and scale was nearly replicated on shark skin metal mould by electroforming. Template made by vacuum casting had clear groove and scale structure. Nevertheless, the phenomenon of the existing of fillet on shark skin metal mould was serious, which had relationship with the complex structure on shark skin. So we can draw the conclusion of that, vacuum casting method is a relatively perfect shark skin replication method.更多还原