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Analysis of chaotic mixing in two model systems

Published online by Cambridge University Press:  21 April 2006

D. V. Khakhar
Affiliation:
Department of Chemical Engineering, Goessmann Laboratory, University of Massachusetts, Amherst, MA 01003, USA
H. Rising
Affiliation:
Department of Mathematics, University of Massachusetts, Amherst, MA 01003, USA
J. M. Ottino
Affiliation:
Department of Chemical Engineering, Goessmann Laboratory, University of Massachusetts, Amherst, MA 01003, USA

Abstract

We study the chaotic mixing in two periodic model flows, the ‘tendril–whorl’ flow and the ‘Aref-blinking-vortex’ flow, with the objective of supplying evidence for the primary mechanisms responsible for mixing in two-dimensional deterministic flows. The analysis is based on tools of dynamical systems theory but it is clear that the mixing problem generates several questions of its own: low periodic points and horseshoes dominate the picture, since we want to achieve mixing quickly; Poincaré sections, popular in dynamical systems analyses, might give misleading information with regard to dispersion at short times. Our analysis shows that both flows are able to stretch and fold material lines well below the lengthscale of the flows themselves. The inner workings of the two systems are revealed by studying the local and global bifurcations. Computations for the blinking-vortex system indicate the existence of an optimum period at which the average efficiency is maximized, whereas the intensity of segregation – a classical parameter in mixing studies – decays rapidly to an asymptotic value in the globally chaotic region. Even though our flows are not turbulent the results might have some implications for pointing to the limits of similar studies in actual turbulent flows (e.g. line stretching).

Type
Research Article
Copyright
© 1991 Cambridge University Press

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