Lubricating Grease Shear Flow and Boundary Layers in a Concentric Cylinder Configuration

Li, Jinxia; Westerberg, Lars-Göran; Höglund, Erik; Lugt, Piet M.; Baart, Pieter

doi:10.1080/10402004.2014.937886

Cited by 19 publications

(21 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Wall slip is for instance not considered in rheometers and the grease is assumed to be uniformly sheared throughout the gap. A couple of papers by the authors have shown that these conditions in fact are violated for the case of grease flow [29,18]. A consequence of this is the question how reliable the values from a rheometer are in terms of grease rheology.…”

Section: Resultsmentioning

confidence: 99%

“…Radulescu et al [24] investigated the flow in pipes with discontinuities, which also could be applied to the flow in bearings. This work is a continuation of previous studies of the flow in closed straight channels [29,17] and in a 3D double restriction seal geometry [14,1,18]. A channel with a 90 • elbow is used and an analytical model of the flow is developed and combined with experimental data from micro Particle Image Velocimetry (µPIV) measurements of the flow in the elbow.…”

Section: Introductionmentioning

confidence: 96%

“…In the studies by Li et. al [18] and Westerberg et. al [29] it is also shown that K and τ 0 have larger impact on the flow as they span over larger magnitudes.…”

Section: R ∂ ∂Rmentioning

confidence: 99%

“…The Herschel-Bulkley rheology model is considered to govern the relation between the shear forces and the shear rate in the grease. In cylindrical coordinates and for the present flow condition (u = u ϕ (r)) the Herschel-Bulkley model reads [18] …”

Section: Analytical Model Of the Flow In The Channel Elbowmentioning

confidence: 99%

“…The concept of wall slip can be divided into two categories: i) true slip, where there is a discontinuity in the velocity field at the fluid-solid interface, and ii) apparent slip, where there is an inhomogeneous thin layer of a fluid adjacent to the wall with different rheological properties to the bulk of fluid enabling fluid movement [27]. Li et al [19] also showed that in a free-surface flow oil bleeding is present where the grease is sheared. This result supports the idea of oil bleeding being responsible for wall slip as oil bleeding in connection to the walls in closed (channel) flows in turn is supported by the high shear stresses close to the solid boundaries.…”

Section: Wall Slip and Flow Evolution In The Elbow Channelmentioning

confidence: 99%

See 4 more Smart Citations

Grease flow in an elbow channel

Westerberg

Farré-Lladós

et al. 2015

Tribol Lett

Self Cite

View full text Add to dashboard Cite

Lubricating greases are materials characterized by a complex nonNewtonian rheology. This study is a continuation of previous studies on the coupling between grease rheology and grease flow in a straight channel-and concentric cylinder geometry. The problem has been modeled and validated with experiments. Here the flow in an elbow channel introducing a non-symmetric distribution of shear stress throughout the cross section of the channel elbow, as well as varying shear rates through the transition from the channel 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 investigated showing that the flow is sensitive to the pressure in the angular (ϕ) direction of the elbow. For high flow rates it is shown that flow separation occur with a resulting circulation in the elbow.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

“…In the studies by Li et. al [18] and Westerberg et. al [29] it is also shown that K and τ 0 have larger impact on the flow as they span over larger magnitudes.…”

Section: R ∂ ∂Rmentioning

confidence: 99%

Section: Analytical Model Of the Flow In The Channel Elbowmentioning

confidence: 99%

Section: Wall Slip and Flow Evolution In The Elbow Channelmentioning

confidence: 99%

See 3 more Smart Citations

Grease flow in an elbow channel

Westerberg

Farré-Lladós

et al. 2015

Tribol Lett

Self Cite

View full text Add to dashboard Cite

show abstract

Dynamic rheological properties of a fumed silica grease

2017

View full text Add to dashboard Cite

Towards Predicting the Onset of Elastic Turbulence in Complex Geometries

Ekanem

Berg

et al. 2022

Transp Porous Med

View full text Add to dashboard Cite

Flow of complex fluids in porous structures is pertinent in many biological and industrial processes. For these applications, elastic turbulence, a viscoelastic instability occurring at low Re—arising from a non-trivial coupling of fluid rheology and flow geometry—is a common and relevant effect because of significant over-proportional increase in pressure drop and spatio-temporal distortion of the flow field. Therefore, significant efforts have been made to predict the onset of elastic turbulence in flow geometries with constrictions. The onset of flow perturbations to fluid streamlines is not adequately captured by Deborah and Weissenberg numbers. The introduction of more complex dimensionless numbers such as the M-criterion, which was meant as a simple and pragmatic method to predict the onset of elastic instabilities as an order-of-magnitude estimate, has been successful for simpler geometries. However, for more complex geometries which are encountered in many relevant applications, sometimes discrepancies between experimental observation and M-criteria prediction have been encountered. So far these discrepancies have been mainly attributed to the emergence from disorder. In this experimental study, we employ a single channel with multiple constrictions at varying distance and aspect ratios. We show that adjacent constrictions can interact via non-laminar flow field instabilities caused by a combination of individual geometry and viscoelastic rheology depending (besides other factors) explicitly on the distance between adjacent constrictions. This provides intuitive insight on a more conceptual level why the M-criteria predictions are not more precise. Our findings suggest that coupling of rheological effects and fluid geometry is more complex and implicit and controlled by more length scales than are currently employed. For translating bulk fluid, rheology determined by classical rheometry into the effective behaviour in complex porous geometries requires consideration of more than only one repeat element. Our findings open the path towards more accurate prediction of the onset of elastic turbulence, which many applications will benefit. Article Highlights We demonstrate that adjacent constrictions “interact” via the non-laminar flow fields caused by individual constrictions, implying that the coupling of rheological effects and fluid geometry is more complex and implicit. The concept of characterizing fluid rheology independent of flow geometry and later coupling back to the geometry of interest via dimensionless numbers may fall short of relevant length scales, such as the separation of constrictions which control the overlap of flow fields. By providing direct experimental evidence illustrating the cause of the shortcoming of the status-quo, the expected impact of this work is to challenge and augment existing concepts that will ultimately lead to the correct prediction of the onset of elastic turbulence.

show abstract

Lubricating Grease Shear Flow and Boundary Layers in a Concentric Cylinder Configuration

Cited by 19 publications

References 16 publications

Grease flow in an elbow channel

Grease flow in an elbow channel

Dynamic rheological properties of a fumed silica grease

Towards Predicting the Onset of Elastic Turbulence in Complex Geometries

Contact Info

Product

Resources

About