Abstract
In this paper, numerical simulations of particle migration in lubricating grease flow are presented. The rheology of three lithium greases with NLGI (National Lubricating Grease Institute) grades 00, 1 and 2 respectively are considered. The grease is modeled as a single-phase Herschel–Bulkley fluid, and the particle migration has been considered in two different grease pockets formed between two concentric cylinders where the inner cylinder is rotating and driving the flow. In the wide grease pocket, the width of the gap is much smaller compared to the axial length scale, enabling a one-dimensional flow. In the narrow pocket, the axial and radial length is of the same order, yielding a three-dimensional flow. It was found that the change in flow characteristics due to the influence of the pocket lateral boundaries when going from the wide to the narrow pocket leads to a significantly shorter migration time. Comparing the results with an existing migration model treating the radial component contribution, it was concluded that a solution to the flow in the whole domain is needed together with a higher order numerical scheme to obtain a full solution to the particle migration. This result is more pronounced in the narrow pocket due to gradients in the flow induced by the lateral boundaries.
Highlights
Lubricating greases are non-Newtonian, semi-solid materials used in many applications such as bearings, gears and railway lubrication
The first part is comprised of modeling the velocity field in the grease pocket
The commercial software Comsol Multiphysics v.5.3 is used to numerically model particle migration in a grease pocket where the flow is driven by a rotating shaft
Summary
Lubricating greases are non-Newtonian, semi-solid materials used in many applications such as bearings, gears and railway lubrication. Grease lubrication reduces friction losses; it contributes to reduced wear and heat transfer in the mechanical systems [1,2]. The sticky and adhesive grease consistency enhances the water-tightness of the sealing and prevents contaminant particles entering a system to reach the lubricated contacts [3]. The grease sealing properties increase with a higher consistency (thicker grease), but at the cost of a higher yield stress value, which in turn may reduce the grease lubricating properties, as the grease ability to flow is reduced. Focusing on grease particle migration, Li et al [5] studied the effect of channel restrictions on the grease flow and how the restrictions affect the particle migration
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