A Parametric Study of a Porous Self-Circulating Hydrodynamic Bearing

This paper is presenting a 3D, isothermal numerical analysis of a cylindrical porous journal bearing characterized by a self-circulating lubricating system that eliminates the necessity of an external circulating pump. The system includes a stationary porous bushing whose inner diameter faces the bearing clearance while the outer diameter faces a wrapped-around reservoir. The loaded, eccentric shaft is generating a high pressure zone in the convergent region followed by a low pressure zone in the divergent region causing the fluid to circulate naturally between the bearing clearance and the reservoir, as it passes through the porous bushing. The fundamental physics of the circulating mechanism are described, and its operation is numerically simulated. The study uses the complete 3D Navier–Stokes Equations (NSE) for the fluid motion in the bearing clearance and the adjacent reservoir. The flow inside the porous matrix is modeled using the Brinkman formulation with added pressure ‘penalties’ brought by the addition of the Darcy and Forchheimer terms. The bearing operates in the fully hydrodynamic lubricating regime disregarding surface roughness effects. A cavitation model proposed by Singhal et al. (2002 [1]) is utilized in the numerical simulation to account for flow and pressure characteristics in the divergent region. The parameters used during the simulations are angular velocity, permeability, porosity, reservoir depth and shaft eccentricity. The results which include the flow patterns, pressure maps and attitude angles, are presented on a parametric basis, and confirm the functionality of the proposed self-circulating system. It was found that the load capacity decreases and the attitude angle increase as permeability increases, and depending on permeability ranges, the increase in the reservoir depth may result in a reduction of the load capacity. Further, certain combinations of geometric parameters and permeability values render the pressure build-up independent of the reservoir depth. Because an optimal configuration requires both a large fluid mass flows through the porous bed (for cooling purposes) and a large load carrying capability, two variables at odds with each other in the present model, an interactive parametric analysis is essential in order to optimize the load carrying capacity versus geometric and operational parameters