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Title: Reaction enhancement of initially distant scalars by Lagrangian coherent structures

Turbulent fluid flows have long been recognized as a superior means of diluting initial concentrations of scalars due to rapid stirring. Conversely, experiments have shown that the structures responsible for this rapid dilution can also aggregate initially distant reactive scalars and thereby greatly enhance reaction rates. Indeed, chaotic flows not only enhance dilution by shearing and stretching but also organize initially distant scalars along transiently attracting regions in the flow. To show the robustness of this phenomenon, a hierarchical set of three numerical flows is used: the periodic wake downstream of a stationary cylinder, a chaotic double gyre flow, and a chaotic, aperiodic flow consisting of interacting Taylor vortices. We demonstrate that Lagrangian coherent structures (LCS), as identified by ridges in finite time Lyapunov exponents, are directly responsible for this coalescence of reactive scalar filaments. When highly concentrated filaments coalesce, reaction rates can be orders of magnitude greater than would be predicted in a well-mixed system. This is further supported by an idealized, analytical model that was developed to quantify the competing effects of scalar dilution and coalescence. Chaotic flows, known for their ability to efficiently dilute scalars, therefore have the competing effect of organizing initially distant scalars along themore » LCS at timescales shorter than that required for dilution, resulting in reaction enhancement.« less
Authors:
;  [1] ;  [2]
  1. Department of Civil, Environmental and Architectural Engineering, University of Colorado, Boulder, Colorado 80309-0428 (United States)
  2. Department of Applied Mathematics, University of Colorado, Boulder, Colorado 80309-0526 (United States)
Publication Date:
OSTI Identifier:
22403218
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Fluids (1994); Journal Volume: 27; Journal Issue: 3; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CHAOS THEORY; COALESCENCE; DILUTION; FILAMENTS; LAGRANGIAN FUNCTION; LYAPUNOV METHOD; PERIODICITY; REACTION KINETICS; SCALARS; SHEAR; STIRRING; TURBULENT FLOW; VORTICES