Hydrodynamic instability of extensional flow

The stability analysis for sheet stretching recently presented by Minoshima and White for Newtonian fluids is repeated for non-Newtonian fluids. For that purpose a constitutive law for nearly extensional flow is derived which, apart from a restriction to short memory of the fluid, is generally valid. Using this constitutive law the result found by Minoshima and White is generalized. Application of the general result to a Maxwell-type fluid shows that the elasticity of the fluid has a stabilizing influence.