Further observations of elastic effects in tubular entry flows

Abstract

The current understanding of tubular entry flows for Newtonian fluids and the influence of elasticity on these flows in the absence of shear thinning and significant fluid inertia is reviewed. While tubular entry flow for Newtonian fluids both with and without fluid inertia is now a solved problem, no single worker has been able to predict any of the significant elastic effects observed for constant viscosity elastic liquids in such flows. New elastic flow phenomena are reported which complicate the problem even more. Two distinctly different flow patterns are observed in a four to one contraction for two constant viscosity elastic fluids with essentially the same characteristics times. Tubular entry flows of elastic liquids develop (with increasing λγ) in the same way only if the contraction ratio is high enough. At sufficiently low contraction ratio, a lip vortex (at the tube entrance) and a corner vortex (in the upstream tube corner) can both be present and interacting with the lip vortex dominating the flow when vortex enhancement and growth occurs. The entry flow problem for elastic liquids is far more complex than originally imagined and is indeed a challenge for numerical simulation and selection of constutitive equations.