title: Mixing through stirring of steady flow in small amplitude helical tubes.
abstract: In this paper we numerically simulate flow in a helical tube for physiological conditions using a co-ordinate mapping of the Navier-Stokes equations. Helical geometries have been proposed for use as bypass grafts, arterial stents and as an idealized model for the out-of-plane curvature of arteries. Small amplitude helical tubes are also currently being investigated for possible application as A-V shunts, where preliminary in vivo tests suggest a possibly lower risk of thrombotic occlusion. In-plane mixing induced by the geometry is hypothesized to be an important mechanism. In this work, we focus mainly on a Reynolds number of 250 and investigate both the flow structure and the in-plane mixing in helical geometries with fixed pitch of 6 tube diameters (D), and centerline helical radius ranging from 0.1 D to 0.5 D. High-order particle tracking, and an information entropy measure is used to analyze the in-plane mixing. A combination of translational and rotational reference frames are shown to explain the apparent discrepancy between flow field and particle trajectories, whereby particle paths display a pattern characteristic of a double vortex, though the flow field reveals only a single dominant vortex. A radius of 0.25 D is found to provide the best trade-off between mixing and pressure loss, with little increase in mixing above R=0.25 D, whereas pressure continues to increase linearly.
authors.affiliation: Department of Aeronautics, Imperial College London, South Kensington, London SW7 2AZ, UK.
authors.forename: A N
authors.initials: AN
authors.lastname: Cookson
authors.forename: D J
authors.initials: DJ
authors.lastname: Doorly
authors.forename: S J
authors.initials: SJ
authors.lastname: Sherwin
mesh_terms: D000818:Animals; D003198:Computer Simulation; D019277:Entropy; D008954:Models, Biological; D008962:Models, Theoretical; D010316:Particle Size; D055585:Physical Phenomena; D012399:Rotation