In this study, the flow of lubricating greases in a labyrinth seal geometry is studied using microparticle image velocimetry (µPIV). The aim is to evaluate the grease velocity distribution inside the gap of a labyrinth seal and to find a relationship between the grease consistency and the transferred speed from the rotating ring in order to choose the correct grease as a sealing medium. In addition, the grease flow characteristics are important for the understanding of fracture due to grease layer displacement. For these purposes, four greases with different rheological properties were used in µPIV experiments. It was found that the grease consistency plays a crucial role in speed development as well as the grease composition and presence of a slip effect at the grease–rotating wall interface.

This article presents numerical simulations of the laminar flow of lubricating greases in a channel with rectangular cross section. Three greases with different consistencies (NLGI grades 00, 1, and 2) have been considered in three different configurations composed of a rectangular channel without restrictions, one rectangular step restriction, and one double-lip restriction. The driving pressure drop over the channel spans from 30 to 250 kPa. The grease rheology is described by the Herschel-Bulkley rheology model, and both the numerical code and rheology model have been validated with analytical solutions and flow measurements using micro-particle image velocimetry.

In this paper, numerical simulations of lubricating grease flow in the grease pocket of a double restriction seal geometry using computational fluid dynamics are presented. The grease is treated as a single-phase Herschel–Bulkley fluid with different rheological properties corresponding to NLGI grade 00, 1 and 2. The numerical code and rheology model have been validated with a semi-analytical solution based on flow measurements using microparticle image velocimetry. The flow has been modelled for low and high rotational speeds driving the flow, and elevated temperatures. Also, the evolution of contaminant particles in the grease pocket is investigated. It was found that the flow and velocity distribution in the pocket—and consequently the contaminant particle concentration evolution, is characterized by the shear thinning rheology of the grease. With higher shear rates in the grease and higher temperatures, the grease approaches a more Newtonian type of behaviour leading to a reduced yield and shear thinning characteristics directly affecting the grease ability to transport contaminant particles.

The behavior of a wet clutch during engagement is of great importance to the durability of the clutch and the drivability of a vehicle. While many different factors influence the engagement behavior, the focus of this paper is to investigate only one factor, the permeability of the wet clutch friction material. Two test cells for measuring the permeability of friction material mounted on clutch discs have been developed. The test cells were then used to examine the effect of clutch material ageing through clutch engagement on the permeability of the material. The tests were performed on full size friction discs including the steel core prior and subsequent to testing in a wet clutch engagement test rig. The ability of the friction material to allow for oil flow both through the sliding surface layer and the bulk of the material was measured. The results indicate that repeated clutch engagements will increase the bulk permeability. However, the repeated engagements will decrease the ability to pass fluid through the friction material sliding surface. This contradictory behavior could be explained by a combination of an increase in pore size through repeated compression and the surface glaze clogging of the friction interface surface pores.

Grease lubrication is traditionally used in a great variety of mechanicalsystems such as rolling bearings, seals, and gears where it has beenshown more advantageous than oil, mainly due to its consistencyallowing the grease to stay inside the system and not leak out. Freesurface effects play an important role in rolling bearings and opengears as the configuration normally is filled with about 30% grease toavoid heavy churning. In this study an analytical model of thestationary uniform flow on a rotating disc is developed and validatedwith experiments. The model results in the velocity profile for the flowin the thin fully yielded viscous layer in connection to the surface aswell as an expression for the plug flow region on top of the viscouslayer. Experiments with two different greases having NLGI grade 1 and2 respectively shows it is possible to obtain a good fit with theanalytically obtained thickness using the rheological parameters foractual greases.

Being able to fully model the flow dynamics of grease, including phase separation, will be highly valuable in the design of lubricated machine elements such as rolling element bearings. Complete models will also be a valuable tool in the process of providing tailor-made greases for different applications. An understanding of the grease flow dynamics enables prediction of grease distribution for optimum lubrication and for the migration of wear- and contaminant particles. In this paper the potential of combined analytical modelling, flow visualizations, and numerical modelling in grease flow dynamics is presented. Specifically, the relation between the rheology of the grease and its impact on the flow motion is of interest in combination with validation of the numerical models in simplified geometries. The numerical models then enable simulations in more complex geometries of particular interest for the grease and bearing industry. It is shown that grease flow is heavily influenced by its non-Newtonian properties and the shear rates in the contact, resulting in distinct regions of yielded and un-yielded grease. Further, the numerical models are shown to match well with experiments and analytical models, enabling numerical models on more complicated geometries.

Being able to model the flow dynamics of grease is highly valuable in the design of lubricated machine elements such as rolling element bearings. An understanding of the grease flow dynamics enables prediction of grease distribution for optimum lubrication and for the migration of wear- and contaminant particles. In this paper the potential of combined analytical modelling, flow visualizations, and numerical modelling in grease flow dynamics is presented. Specifically, the relation between the rheology of the grease and its impact on the flow motion is of interest in combination with validation of the numerical models in simplified geometries. The numerical models then enable simulations in more complex geometries of particular interest for the grease and bearing industry. It is shown that grease flow is heavily influenced by its non-Newtonian properties and the shear rates in the contact, resulting in distinct regions of yielded and un-yielded grease. Further, the numerical models are shown to match well with experiments and analytical models, enabling numerical models on more intricate geometries in the bearing industry.

Grease flow in grease lubricated systems can often be qualified as free-surface flow. It occurs for example in rolling bearings after the churning phase or on open gears. Here only a fraction of the bearing or gearbox volume is filled with grease. Part of the grease is flowing in relatively thin layers induced by centrifugal forces caused by rotation of the various components. In this paper a model problem is investigated in the form of a free-surface flow of grease on a rotating disc. Experiments have been performed where the onset of flow and remaining grease have been studied varying the surface roughness, temperature and the centrifugal forces. The experiments have been coupled to analytical models describing the flow and temperature distribution in the grease. It was found that the impact of surface roughness could be neglected. The flow is determined by the centrifugal forces and rheology of the grease. Temperature effects the rheology but also the oil separation creating low shear strength/low viscosity layers at the surface.

The flow of lubricating greases in an elbow channel has been modeled and validated with velocity profiles from flow visualizations using micro-particle image velocimetry. The elbow geometry induces a nonsymmetric distribution of shear stress throughout its cross section, as well as varying shear rates through the transition from the elbow inlet to the outlet. The flow has been modeled both for higher flow rates and for creep flow. The influence of the grease rheology and flow conditions to wall slip, shear banding and an observed stick–slip type of motion observed for low flow rates are presented. The effect on the flow of the applied pressure is also modeled showing that the flow is sensitive to the pressure in the angular ( ϕ ) direction of the elbow. For high pressures, it is shown that the flow is reversed adjacent to the elbow walls.