Kp. Chen, HYPERBOLICITY AND CHANGE OF TYPE IN STEADY CO-EXTRUSION FLOW OF UPPER-CONVECTED MAXWELL FLUIDS, Journal of non-Newtonian fluid mechanics, 47, 1993, pp. 157-167
The linearized equations governing the steady axisymmetric co-extrusio
n flow of two upper-convected Maxwell fluids through a circular die ar
e studied and conditions are found under which the vorticity equation
can change its type from elliptic to hyperbolic in the core and the an
nulus regions.