INSTABILITY OF THE LARGE REYNOLDS-NUMBER FLOW OF A NEWTONIAN FLUID OVER A VISCOELASTIC FLUID

The stability of the large Reynolds number flow of a Newtonian fluid o ver a much more viscous viscoelastic fluid is studied via a linear ana lysis. The two fluids are confined within a channel and the flow is dr iven by the motion of the plate bounding the Newtonian fluid. Matched asymptotic expansions are used to derive the dispersion relation, and the flow is found to be always unstable to an interfacial mode due to the discontinuity in the fluid viscosities. It is shown that even a sm all amount of elasticity of the viscoelastic fluid can change the stab ility characteristics considerably.