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LAMINATION AND MIXING IN CANONICAL AND TURBULENT FLOWS

Sylvain Lardeau
Laboratoire d'Etudes Aérodynamiques UMR 6609, Université de Poitiers, Téléport 2 - Bd. Marie et Pierre Curie B.P. 30179, 86962 Futuroscope Chasseneuil Cedex, France; Imperial College London, Department of Aeronautics, UK

Lionel Rossi
Department of Aeronautics, Imperial College London London, SW7 2AZ, United Kingdom

D. Doorly
Imperial College London London United Kingdom

A. Durant
Imperial College London London United Kingdom

D. Kustrin
Imperial College London London United Kingdom

F. Schwander
Ecole Centrale Marseille Marseille France

要約

Lamination and mixing properties are characterised for a canonical flow (cat's eyes flip) at low Reynolds number (Re~13) and a turbulent flow. The cat's eyes flow is experimentally driven by electromagnetic forces while the turbulent flow is generated using 2D DNS. It is shown that lamination and stretching grow exponentially for both flows with an exponent higher for the stretching than for the lamination. Noticeably, the difference between the stretching and lamination exponents is higher for the turbulent flow than for the low Reynolds number flow with ratios respectively about 1.32 and 1.12. Moreover, lamination enhances mixing locally by reducing the distance over which diffusion needs to act to finalise mixing. The difference in the mixing properties of the flows is related to the distribution of lamination. The turbulent flow saturates locally, i.e. it reaches locally high lamination values where diffusion can act swiftly over short distances to finalise mixing while most of the flow is still with low values of lamination. This leads to an algebraic growth of the mixing coefficient. The cat's eyes flip flow globally increases lamination with a better space filling than the turbulent flow. This delays the saturation of mixing and leads to an initial exponential growth of the mixing coefficient.