Abstract
An interfacial stability analysis for two superposed inelastic power law and elastic second-order fluids in plane poiseuille flow has been carried out utilizing both asymptotic and spectral based numerical techniques. The effect of viscosity, density, depth and elasticity ratio have been investigated. Our results indicate that shear thinning viscosity and elasticity play an important role in determining the interfacial stability at all wave numbers. Computational results also show the possibility of obtaining stable interfaces at all disturbance wavelengths. This suggests that operating diagrams for stable flow of multilayer polymeric fluids could be constructed based on this analysis.