表面粗糙度对接触界面间流体流动的影响

发布时间：2018-05-20 00:23

本文选题：接触界面 + 层流流动　；参考：《合肥工业大学》2016年硕士论文

【摘要】：两个固体表面在压力作用下接触,表面凸起形成了间隙仅为微米或纳米级别的接触界面。接触界面间的液体流动对整个系统的性能有很大的影响。接触界面间的微小间隙形成了微通道,微通道广泛地存在于各种微型设备中。微型设备在微机电系统、计算机、生物、医疗、航空航天、通讯和国防上有着巨大的应用前景。由于通道尺寸急剧减小,液体在接触界面间流动时,会受到很多因素的影响,流动表现出与常规尺度不同的新现象。其中,表面粗糙度直接决定了接触间隙的大小,是影响流动的重要因素。本文针对接触界面间的流动,利用有限元软件Fluent,数值分析了界面间流体的流动特性。首先采用规则微凸体模拟表面粗糙度,用平行平板简化接触界面,建立了二维和三维的粗糙接触界面间流动模型,并对两种模型进行数值模拟,考虑相对粗糙度和面积比对界面间层流流动的速度分布、压力分布、壁面切应力分布、回流和阻力特性等的影响；其次,验证了粗糙表面具有自仿射特性,采用分形理论模拟粗糙表面轮廓,建立了单个和两个粗糙曲面的分形接触模型,同样利用数值分析的方法对界面间层流流动进行模拟,得到了分形维数和表面粗糙度对界面间流动的影响。研究表明：(1)微凸体的存在可以等效于管径的缩小,即使在层流区2%的相对粗糙度便会对层流流动产生不容忽略的影响。(2)微凸体的存在引起了回流,认为界面间层流阻力增加的来源是微凸体附近由于回流带来的较大压差阻力。壁面切应力随微凸体形状而变化,在微凸体顶端达到最大值,证实了阻力主要来自微凸体顶端；用微凸体模拟粗糙度可简化实际复杂表面,通过改变微凸体的结构和分布,可以分析工程中接触界面间的流动问题。(3)表明粗糙度轮廓具有多尺度、自仿射的特性。采用分形理论可以简化对粗糙表面的表征,构造的表面更加符合实际表面的复杂分布,更能真切地描述表面的性质。(4)对单个粗糙表面和两个粗糙表面的分形接触模型进行分析,研究表明：流动最大速度随表面粗糙度的增大而增大；压力在波峰处上升,在波谷处下降；壁面切应力随表面形貌而波动。采用分形理论模拟实际粗糙表面,有助于对复杂工程表面进行分类研究,具有很大的研究价值。
[Abstract]:When the two solid surfaces are in contact with each other under pressure, the surface protrusions form contact interfaces with only micro- or nanoscale gaps. The liquid flow between the contact interfaces has great influence on the performance of the whole system. The micro gap between the contact interfaces forms microchannels, which widely exist in various microdevices. Micro-equipment has great application prospect in MEMS, computer, biology, medical, aerospace, communication and national defense. Due to the sharp reduction of channel size, the flow between the contact interfaces will be affected by many factors, and the flow shows a new phenomenon different from the conventional scale. Among them, the surface roughness directly determines the size of the contact gap and is an important factor affecting the flow. In this paper, the flow characteristics of interfacial fluid are numerically analyzed by means of finite element software Fluentfor the flow between contact interfaces. Firstly, the surface roughness is simulated by regular microconvex body, and the contact interface is simplified by parallel plate. Two and three dimensional flow models between rough contact interfaces are established, and the two models are numerically simulated. The effects of relative roughness and area ratio on velocity distribution, pressure distribution, wall shear stress distribution, circumfluence and resistance characteristics of laminar flow between interfaces are considered. Fractal theory is used to simulate rough surface contours and fractal contact models of single and two rough surfaces are established. The laminar flow between interfaces is also simulated by numerical analysis. The effects of fractal dimension and surface roughness on the interfacial flow are obtained. The study shows that the existence of the microconvex body can be equivalent to the reduction of the diameter of the pipe, even if the relative roughness of 2% in the laminar flow region will have an unnegligible effect on the laminar flow. It is considered that the source of the increase of laminar flow resistance between interfaces is the large pressure differential resistance caused by the reflux near the microconvex body. The wall shear stress varies with the shape of the microconvex body and reaches the maximum at the top of the microconvex body, which confirms that the resistance mainly comes from the tip of the microconvex body, and the simulation roughness of the microconvex body can simplify the actual complex surface by changing the structure and distribution of the microconvex body. The flow problem between contact interfaces in engineering can be analyzed. It is shown that the roughness profile has multi-scale and self-affine characteristics. The fractal theory can simplify the representation of rough surfaces, and the constructed surfaces are more consistent with the complex distribution of real surfaces, and can describe the properties of the surfaces more truthfully. (4) the fractal contact models of single rough surfaces and two rough surfaces are analyzed. The results show that the maximum velocity of flow increases with the increase of surface roughness, the pressure increases at the peak and decreases at the trough, and the wall shear stress fluctuates with the surface morphology. Using fractal theory to simulate the actual rough surface is helpful to the classification of complex engineering surfaces and has great research value.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TH117

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