Finite Volume Modeling of Gas Flow in Microbearings with Rough Surface Topography

Abstract

abstractThe random surface roughness effects on the performances of gas-lubricated slider microbearings are investigated using finite volume analysis. The rough surface morphologies with the atomic force microscope (AFM) data and the numerical procedures used to generate self-affine surfaces by the midpoint displacement method are proposed and compared. Three-dimensional finite volume modeling of the gas microbearing and its flow field mesh are described considering the velocity-slip boundary condition. The results indicate that surface roughness causes a deviation in the pressure distribution, load-carrying capacity, velocity profile, and local Reynolds number from conventional theory with various values depending on the degree of surface roughness used. The pressure decreases irregularly due to the fractal surface and produces a larger change. The larger the roughness exponent is, the larger the gas slip velocity at the bottom of the wall. In addition, the velocity-slip boundary condition can cause a decrease in the gas flow velocity. The surface roughness effect also leads to random variations in the local Reynolds number. This demonstrates that the random surface roughness potentially causes very complicated flow behavior in the ultra-thin-film bearing lubrication in microelectromechanical systems (MEMS) and should be adequately characterized in terms of the fractal nature of the bearing surfaces.