Statistical independence of the initial conditions in chaotic mixing

J. M. García de la Cruz, J. C. Vassilicos, and L. Rossi
Phys. Rev. E 96, 052212 – Published 17 November 2017

Abstract

Experimental evidence of the scalar convergence towards a global strange eigenmode independent of the scalar initial condition in chaotic mixing is provided. This convergence, underpinning the independent nature of chaotic mixing in any passive scalar, is presented by scalar fields with different initial conditions casting statistically similar shapes when advected by periodic unsteady flows. As the scalar patterns converge towards a global strange eigenmode, the scalar filaments, locally aligned with the direction of maximum stretching, as described by the Lagrangian stretching theory, stack together in an inhomogeneous pattern at distances smaller than their asymptotic minimum widths. The scalar variance decay becomes then exponential and independent of the scalar diffusivity or initial condition. In this work, mixing is achieved by advecting the scalar using a set of laminar flows with unsteady periodic topology. These flows, that resemble the tendril-whorl map, are obtained by morphing the forcing geometry in an electromagnetic free surface 2D mixing experiment. This forcing generates a velocity field which periodically switches between two concentric hyperbolic and elliptic stagnation points. In agreement with previous literature, the velocity fields obtained produce a chaotic mixer with two regions: a central mixing and an external extensional area. These two regions are interconnected through two pairs of fluid conduits which transfer clean and dyed fluid from the extensional area towards the mixing region and a homogenized mixture from the mixing area towards the extensional region.

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  • Received 12 January 2017

DOI:https://doi.org/10.1103/PhysRevE.96.052212

©2017 American Physical Society

Physics Subject Headings (PhySH)

Nonlinear DynamicsFluid Dynamics

Authors & Affiliations

J. M. García de la Cruz* and J. C. Vassilicos

  • Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom

L. Rossi

  • CEA, Paris-Saclay University, Den-STMF, Gif-sur Yvette F-91191, France

  • *marcos@imperial.ac.uk

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Issue

Vol. 96, Iss. 5 — November 2017

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