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Published August 1981 | Published
Journal Article Open

Structure in turbulent mixing layers and wakes using a chemical reaction


Plane turbulent mixing between two streams of water which contained dilute chemical reactants was studied in a new blow-down water tunnel. In a diffusion-limited reaction, a pH indicator, phenolphthalein, in one stream mixed and reacted with a base, sodium hydroxide, in the other stream to form a visible reaction product. The product was found to exist, as expected, in concentrated regions associated with the large, span-wise-coherent structures of the turbulence. A transition in the mixing was observed in which the aqueous mixing product increased by an order of magnitude. The transition is a consequence of the appearance and development of small-scale three-dimensional motions in the flow. Downstream of the transition, the amount of mixing product was independent of Reynolds number (for an order-of-magnitude increase in the latter) and at most only weakly dependent on Schmidt number.

Additional Information

© 1981 Cambridge University Press. Received 7 March 1980. Published online: 20 April 2006. The author is indebted to Professor Anatol Roshko for his guidance and advice during the course of these experiments. The ideas presented here were developed during discussions with the faculty and students of the Graduate Aeronautioal Laboratory (GALCIT). Most of the wake measurements were done with the help of Till W. Liepmann. The author also wishes to acknowledge the significant contributions of James E. Broadwell, Garry L. Brown, and Anatol Roshko in reviewing the manuscript. The work was made possible by the Air Force Office of Scientific Research under contract F44620-76-C-0046.

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