Non-linear viscoelastic friction reduction in the short length journal bearing

Viscoelastic fluids in shear produce normal stresses. In rotating devices, these normal stresses produce a non-zero pressure field that would not exist in the same flow conditions with purely viscous fluids. This additional elastic pressure field has been used to increase the load carrying capacity and decrease the coefficient of friction in thrust bearings and infinitely long journal bearings, and that same analysis has been extended to the short length journal bearing. Here, the Cauchy momentum equations in polar coordinates are solved in the thin film limit for both velocity and pressure. Non-linear viscoelastic behavior is included through the CEF model, which predicts shear thinning for the viscosity and the normal stresses. Because of the short length bearing approximations the normal stress and viscous effects can be considered separately. The purely viscous contributions result in a model that resembles the Reynolds equation (a restatement of conservation of mass and momentum for a purely viscous fluid) for a short length journal bearing, and the purely viscous results match the predictions of the Reynolds equation over all eccentricity ratios, validating the model. As normal stress effects are included, the elastic contributions to the pressure and velocity fields increase the load carrying capacity and decrease the coefficient of friction compared to the results with the purely viscous fluid in the same flow conditions. This suggests that non-linear viscoelasticity is beneficial in journal bearing applications, and the model provides bearing designers a way to include non-linear viscoelastic behavior in their designs.