Effects of lubricant additives on the performance of hydrodynamically lubricated journal bearings

Abstract

A non-Newtonian rheological model to investigate theoretically the effects of lubricant additives on the steady state performance of hydrodynamically lubricated finite journal bearings is introduced. In this model, the non-Newtonian behavior resulting from blending the lubricant with polymer additives is simulated by Stokes couple stress fluid model. The formed boundary layer at the bearing surface is described through the use of a hypothetical porous medium layer that adheres to the bearing surface. The Brinkman-extended Darcy equations are utilized to model the flow in the porous region. A stress jump boundary condition is applied at the porous media/fluid film interface. A modified form of the Reynolds equation is derived and solved numerically using a finite difference scheme. The effects of bearing geometry, and non-Newtonian behavior of the lubricant on the steady-state performance characteristics such as pressure distribution, load carrying capacity, side leakage flow, and coefficient of friction are presented and discussed. The results showed that lubricant additives significantly increase the load carrying capacity and reduce both the coefficient of friction and the side leakage as compared to the Newtonian lubricants.

Comparison of Non-Newtonian Constitutive Laws in Hydrodynamic Lubrication

“…A modified Reynolds equation is numerically solved showing that the presence of couple stress provides a significant increase of the pressure field. More recently, Elsharkawy [23] was interested in the static performance of a compliant bearing lubricated by a polar fluid. More recently still, Lahmar and Bou-Saïd [24] study different types of unsteady loading in a connecting-rod bearing.…”

Tribological properties of 2 novel Mo/B–based lubricant additives in polyalphaolefin

“…In the formulation of lubricating oils, antiwear (AW) and extreme pressure (EP) additives, contained in the additive package, are commonly added to the oil system. Antiwear and EP additives are usually chemically active species that can react with the mechanical contact surface; they are the important component that can inhibit scuffing and seizure and reduce wear between contact surfaces of friction pair …”

Effect of Couple Stress Lubrication on Symmetric Hole-Entry Hybrid Journal Bearing

“…For predicting the behavior of such fluids, Stokes [6] proposed the concept of couple stress theory of fluids. Later on, several investigators analyzed the performance of hydrodynamic journal bearings under couple stress lubricant (Ramanaiah and Sarkar [7], Lin [8], Guha [9], Elsharkawy [10]). Their studies highlighted the advantages of couple stress lubricants over Newtonian lubricants such as increased load carrying capacity, decreased side leakage and friction coefficient.…”