Lubrication theory

About: Lubrication theory is a research topic. Over the lifetime, 1713 publications have been published within this topic receiving 50261 citations. The topic is also known as: Fluid bearing.

Linear stability and nonlinear dynamics in a long-wave model of film flows inside a tube in the presence of surfactant

Abstract: A long-wave model based on lubrication theory is developed for the flow of a viscous liquid film lining the interior of a tube in the presence of an insoluble surfactant on the interface; no thin-film assumption is made. Linear stability analysis identifies two modes; in the absence of base flow, the ‘interface’ mode is the only unstable mode. The growth rates of this mode serve as an accurate predictor of how surfactant concentration increases plug formation time, and the effects of film thickness on this increase are quantified. In the presence of base flow, both the interface mode and ‘surfactant’ mode may be unstable, resulting in a richer variety of free-surface dynamics. In previous work, turning points in families of travelling wave solutions for a falling viscous film lining the interior of a vertical tube with a clean interface have been shown to be a good indicator of , provided the interface mode is linearly stable. When both modes are unstable, interpretation of these turning points as they relate to plug formation is more complicated. The study concludes by examining the impact of film thickness on growth rates and travelling wave solutions for core–annular flow with surfactant.

강한 측력이 작용하는 피스톤 펌프의 왕복동 피스톤 기구 부에서의 윤활모형에 관한 연구

Abstract: The objective of this study is to model and simulate the nonlinear lubrication performance of the sliding part between the piston and cylinder wall in a hydrostatic swash-plate-type axial piston pump. A numerical algorithm is developed that facilitates simultaneous calculation of the rotating body motion and fluid film pressure to observe the fluid film geometry and power loss. It is assumed that solid asperity contact, so-called mixed lubrication in this study, invariably occurs in the swash-plate-type axial piston pump, which produces a higher lateral moment on the pistons than other types of hydrostatic machines. Two comparative mixed lubrication models, rigid and elastic, are used to determine the reaction force and sliding friction. The rigid model does not allow any elastic deformation in the partial lubrication area. The patch shapes, reactive forces, and virtual local elastic deformation in the partial lubrication area are obtained in the elastic contact model using a simple Hertz contact theory. The calculation results show that a higher reaction force and friction loss are obtained in the rigid model, indicating that solid deformation is a significant factor on the lubrication characteristics of the reciprocating piston part.

Lubricating motion of a sphere in a conical vessel

Abstract: The final stage of sedimentation of a spherical particle moving along the axis of a conical vessel containing a viscous incompressible fluid is studied both theoretically by lubrication analysis and experimentally by laser interferometry. The particle settling velocity varies like d5/2, where d is the gap. There is an excellent agreement between this result from lubrication theory and experiment, the upper bound being for a gap of about 1/30 radius and the lower practical bound being at the size of the particle roughness.

High-Speed Subsonic Compressible Lubrication

Abstract: The present study extends the scope of compressible lubrication theory (CLT) by considering a more complete formulation of compressible flow in a thin film. A one-dimensional (1D) approximation is obtained, which is common in basic studies of compressible flow. A dimensionless formulation of the thin film compressible flow equations (continuity, momentum, energy, and perfect gas) is derived. There are three dimensionless governing parameters, the Mach number M, the compressibility or bearing number Λ, and a heat transfer number H (a sort of inverse Peclet number). The classical theory assumes isothermal conditions (a consequence of a large heat transfer number) and implicitly assumes low Mach number conditions. It turns out that neither of these conditions are met in high-speed applications such as foil bearings. Results are calculated by varying M and H in a parametric fashion. We find that the influence of Mach number is small (at least up to M = 0.5) but the influence of heat transfer is large: the classical predicted results are in error by a factor of four or so. The improved theory predicts much greater load than the traditional. This means that high-speed air bearing design based on CLT would function satisfactorily, as born out by their successful application; however, such bearings would be significantly over-designed.