The analysis is concerned with the effect of fluid-elasticity on the stability of laminar parallel flow. The widely used multigrade oils contain polymer additives that make them viscoelastic. These oils are widely used for high shear-rate laminar flow of hydrodynamic lubrication, where flow instability is undesirable because it significantly increases the viscous friction losses. A fluid model is applied where the stress-relaxation effect is considered in addition to the fluid viscosity. However, the normal stresses are disregarded.
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