CIRCULAR ENTRY FLOWS OF FLUID M1

The observations presented in circular entry flows for fluid M1 can be used to formulate conclusions about other viscoelastic fluids that fall within this general class of fluid behaviour. Evidence reported here shows that the lip and corner vortices observed in contraction flows of fluid M1 can exist either in isolation from each other, or in a figure-eight combination of both. A probable mechanism is proposed for the generation and growth of the lip vortex, based on the presence of an extenstionally formed, solid-like core of fluid near the contraction entry zone. The mechanism is tested using a purely Newtonian numerical simulation in a re-entrant tube entry flow geometry. End correction and extensional viscosity measurements, using orifice pressure drop techniques, reveal a maximum value of both entities and increasingly unstable values beyond those flow conditions. © 1990.