The Effect Of Surface Roughness On Fluid Flow Between Contact Interface

Two solid surfaces are exposed under pressure, and the surface peaks form a contact interface with the micron even nanometer level. The liquid flow in the contact interface has a great influence on the performance of the whole system. The micro gap between the contact interface formed a micro channel, micro channel widely exists in a variety of micro devices. Micro devices have great potential applications in micro electro mechanical systems, computer, biology, medical treatment, aerospace, communications and national defense. Due to the sharp reduction of the channel size, the liquid flow between the interface will be affected by many factors, the flow shows new phenomenon that is different with the conventional scale. The surface roughness directly determines the size of the contact gap, which is an important factor.Based on the flow between rough contact interface, this paper researches the fluid flow characteristics by using f the finite element software Fluent. First, using micro convex body to simulate surface roughness, using parallel plate to simulate the surface roughness, a two dimensional and three dimensional model are established, considering the effect of the relative roughness and area ratio on velocity distribution, pressure distribution, wall shear stress distribution, return and resistance; Secondly, rough surface is verified with the affine properties, fractal theory are adopted to simulate the rough surface, the single and two fractal contact model are set up, to obtain the influence of fractal dimension and surface roughness on the velocity distribution, pressure distribution, wall shear stress distribution and resistance characteristics. Research shows that:(1) The existence of micro convex body can be equivalent to diameter reduction, even 2% relative roughness will lead to big influence that can’t be neglected in laminar flow.(2) The backflow is caused by micro convex, and the large pressure difference induced by backflow is the source of flow resistance increase. Wall shear stress change with micro convex body shape, and reaches maximum at the top of the micro convex body, confirmed that the resistance mainly comes from the top of the micro convex body; Using micro convex body simulation can simplify the actual complex surface roughness, by changing the structure and distribution of micro convex body, the research of flow between contact interface can be analyzed.(3) The roughness profile is multi-scale and self-affine characteristics. By using the fractal theory can simply the characterization of rough surface, the surface is more consistent with the actual distribution of complex surface, can truly describe the nature of the surface.(4) Through the analysis on the single and two rough surface fractal models, the result shows that the maximum flow velocity increases with the surface roughness and pressure rises at the crest of the wave, declines in the trough. Wall shear stress fluctuates according to the surface morphology. Fractal theory are adopted to simulate the actual rough surface, contribute to the classification study on the complex engineering surface, is of great theory value.