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The structure of a chemically reacting plane mixing layer

Published online by Cambridge University Press:  21 April 2006

S. M. Masutani  and
C. T. Bowman
S. M. Masutani
Affiliation:
Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA Present address: Hitachi Research Laboratory, Ibaraki-ken, Japan.
C. T. Bowman
Affiliation:
Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA
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Abstract

Experiments were performed to examine the structure of a chemically reacting, gas-phase, two-stream plane mixing layer. Temporally and spatially resolved measurements of streamwise velocity and of the concentrations of a reactant and product species and a conserved scalar were recorded across the mixing layer at streamwise locations between Redelta; = 730–2520. Non-reacting flow experiments were conducted to establish the entrainment and mixing characteristics of the layer. Reacting flow experiments were performed using dilute concentrations of the reactants, NO and O3, to ensure that the flow field remained isothermal. The probability density functions (p.d.f.s) and associated statistical quantities of the conserved and reactive scalars are compared with results from previous analytical and experimental studies. The data suggest, in concert with the Broadwell-Breidenthal model, that fluid in the mixing layer exists in three states: tongues of unmixed free-stream fluid which, on occasion, stretch across the layer; finite-thickness interfacial diffusion zones of mixed fluid which border the parcels of unmixed fluid; and regions comprising fluid of nearly homogeneous composition. The data also confirm previously reported asymmetry in entrainment rates from the two feed streams and show the important role of molecular diffusion in the mixing process. A fast-chemistry assumption, applied to predict reactive-species concentrations from the measured conserved-scalar p.d.f.s, overestimates the extent of reaction, indicating the importance of finite-rate chemistry for the present conditions. A Damköhler number, based on large-scale mixing times, is shown to be useful in determining the applicability of a fast-chemistry analysis to reacting mixing layers.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 172 , November 1986 , pp. 93 - 126
Copyright
© 1991 Cambridge University Press

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