Effect of viscoelastic fluid on the lift force in lubricated contacts

TL;DR

This study investigates how viscoelastic fluid layers influence the lift force on a nearby moving cylinder, revealing the roles of elasticity, surface tension, and interface slip in modulating the force.

Contribution

It provides a comprehensive analysis of the effects of viscoelasticity, including tangential stress and slip velocity, on lift force in lubricated contacts, extending previous models.

Findings

Lift force depends on the Deborah number, decreasing as the fluid becomes more viscous.

Surface tension can cause the lift force to become negative at small Deborah numbers.

Tangential stress and slip velocity are significant contributors, especially for thin elastic layers.

Abstract

We consider a cylinder immersed in viscous fluid moving near a flat substrate covered by an incompressible viscoelastic fluid layer, and study the effect of the fluid viscoelasticity on the lift force exerted on the cylinder. The lift force is zero when the viscoelastic layer is not deformed, but becomes non-zero when it is deformed. We calculate the lift force by considering both the tangential stress and the normal stress applied at the surface of the viscoelastic layer. Our analysis indicates that as the layer changes from the elastic limit to the viscous limit, the lift force decreases with the decrease of the Deborah number (De). For small De, the effect of the layer elasticity is taken over by the surface tension and the lift force can become negative. We also show that the tangential stress and the interface slip velocity (the surface velocity relative to the substrate), which have been ignored in the previous analysis, give important contributions to the lift force. Especially for thin elastic layer, they give dominant contributions to the lift force.