CFD Modeling of a Thermal and Shear-Thinning Elastohydrodynamic Line Contact

Abstract

In this paper a computational fluid dynamics (CFD) approach for solving elastohydrodynamic lubrication using the freely available package OPENFOAM is introduced. The full Navier–Stokes equations are solved, which enables the entire flow domain to be modeled and all gradients inside the lubricated contact to be resolved. The phenomenon of cavitation is taken into account by employing a homogenous equilibrium cavitation model, which maintains a specified cavitation pressure inside the cavitating region. The energy equation used considers the effects of heat conduction and convection, viscous heating, and the heat of evaporation. The developed method has been applied to a series of cases of lubricated metal-on-metal line contact with an entrainment velocity of uent=2.5m∕s, viscosities η0=[0.01,1]Pas, and slide-to-roll ratios SRR=[0,1,2] under both thermal and isothermal conditions. The isothermal results are compared to the Reynolds theory and most results agree very well. Only the high-viscosity pure rolling case shows small differences. The combined effects of temperature, pressure, and shear-thinning are studied for the thermal cases. A temperature-induced shear band occurs in the case of sliding combined with very large viscosity compared to the isothermal case, which results in significant pressure variations across the thickness of the film. The impact of temperature on the friction force is discussed, showing differences of up to −88.5% compared to the isothermal case. The developed method is capable of giving new insights into the physics of elastohydrodynamic lubrication, especially in cases where the usual assumptions of the Reynolds theory break down.

Through-Thickness Velocity Profile Measurements in an Elastohydrodynamic Contact

“…This is the first published result of a through-thickness 17 velocity profile measurement in an EHL contact. It shows that the velocity profile at this commonly assumed in EHL theory [1,2], and those found using isothermal simulations 23 [45]. It suggests that the fluid experiences different shear rates depending on the distance …”

CFD modeling compared to temperature and friction measurements of an EHL line contact

“…Important examples where CFD has been used to solve EHL include work by Schäfer et al [1] and Almquist and Larson [2] [3], who validated the CFD method against Reynolds solvers and introduced thermal and transient behavior. Hartinger et al [4] also validated a CFD-approach against a Reynolds solver and presented thermal EHL solutions. Bruyere et al [5] presented a CFD approach for the fluid and an FEM approach for the solid, using previously published CFD-data as validation [4] and found satisfying agreement (maximum film thickness deviation between the two series of results lower than 2%) for a non-Newtonian, thermal case.…”

“…Hartinger et al [4] also validated a CFD-approach against a Reynolds solver and presented thermal EHL solutions. Bruyere et al [5] presented a CFD approach for the fluid and an FEM approach for the solid, using previously published CFD-data as validation [4] and found satisfying agreement (maximum film thickness deviation between the two series of results lower than 2%) for a non-Newtonian, thermal case. One case they studied with zero entrainment velocity showed interesting results, explaining the dimple geometry of the film-thickness.…”

Two-scale EHL: Three-dimensional topography in tilted-pad bearings

“…The inclusion of inertial effects via the generalised Reynolds equation [17] or Navier-Stokes equations illustrated the influence of inertia on load capacity and the consequent benefit of using Computational Fluid Dynamics (CFD) to model the fluid film flow. CFD has also been used on smooth geometries to enable the modelling of a range of phenomena which occur in EHL such as thermal transport, rheology, cavitation [18], wall slip [19] and structural models [20]. Both deterministic (where the surface topographical features are fully described and resolved over the global domain) and homogenisation (where the flow about surface topographical features are solved independently and the results are applied to the global domain) models have been used by researchers to analyse bearings with surface texturing.…”