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Annals of Biomedical Engineering

, Volume 37, Issue 4, pp 710–721 | Cite as

Mixing Through Stirring of Steady Flow in Small Amplitude Helical Tubes

  • A. N. Cookson
  • D. J. Doorly
  • S. J. Sherwin
Article

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 0.1D to 0.5D. 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 0.25D is found to provide the best trade-off between mixing and pressure loss, with little increase in mixing above R = 0.25D, whereas pressure continues to increase linearly.

Keywords

Laminar Spectral/hp Graft Shunt Stent Pipe Thrombosis Co-ordinate mapping Advection 

Notes

Acknowledgment

The authors would like to acknowledge the EPSRC for funding this research.

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Copyright information

© Biomedical Engineering Society 2009

Authors and Affiliations

  1. 1.Department of AeronauticsImperial College LondonLondonUK

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