High-pressure rheology of lubricants and limitations of the Reynolds equation

Abstract A review of high pressure rheology leads to the conclusion that the results from rheometers may be used to generate empirical rate equations which are useful in modelling elastohydrodynamic traction. However, an analytical treatment of piezoviscous liquids reveals that the Reynolds equation adequately captures the mechanics of the piezoviscous liquid only when the shear stress is much less than the reciprocal of the pressure viscosity coefficient. Otherwise the cross film pressure gradient may be significant and secondary flows result.