On dominating elastico-viscous response in some complex flows

Abstract

A laser flow-visualization technique is used to study the behaviour of Newtonian and non-Newtonian elastic liquids in complex flows involving abrupt changes in geometry. Particular attention is paid to those situations where dramatic elastico-viscous effects are in evidence and the flow characteristics for non-Newtonian liquids are qualitatively different from those for Newtonian liquids. Consideration is also given to the effect of ‘rounding’ sharp re-entrant corners. Two basic types of geometry are studied in detail. The first is the so-called combined mixing-and-separating flow geometry introduced in an earlier study (Cochrane et al. 1981), while the second includes both planar and circular contractions. Attempts to simulate numerically the observed flows are very satisfactory in the Newtonian case, but the elastico-viscous simulations can do no more than indicate trends in the right direction.