ON VISCOELASTIC EFFECTS IN SWIRLING FLOWS

Viscoelastic effects in pressure-driven flow through a curved pipe of circular cross-section are studied by perturbation methods. Relatively simple constitutive models are studied, including the Upper Convected Maxwell (UCM) fluid. It is shown that in the swirling flow generated by the curvature of the pipe, fluid inertia and viscoelasticity are complementary influences in determining the direction of swirl, in conflict with general expectation. Moreover, for creeping flow of the UCM model, drag reduction followed by drag enhancement is predicted as the pressure gradient generating the flow is systematically increased.