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On density effects and large structure in turbulent mixing layers

Brown, Garry L. and Roshko, Anatol (1974) On density effects and large structure in turbulent mixing layers. Journal of Fluid Mechanics, 64 (4). pp. 775-816. ISSN 0022-1120. doi:10.1017/S002211207400190X.

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Plane turbulent mixing between two streams of different gases (especially nitrogen and helium) was studied in a novel apparatus. Spark shadow pictures showed that, for all ratios of densities in the two streams, the mixing layer is dominated by large coherent structures. High-speed movies showed that these convect at nearly constant speed, and increase their size and spacing discontinuously by amalgamation with neighbouring ones. The pictures and measurements of density fluctuations suggest that turbulent mixing and entrainment is a process of entanglement on the scale of the large structures; some statistical properties of the latter are used to obtain an estimate of entrainment rates. Large changes of the density ratio across the mixing layer were found to have a relatively small effect on the spreading angle; it is concluded that the strong effects, which are observed when one stream is supersonic, are due to compressibility effects, not density effects, as has been generally supposed.

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Additional Information:Copyright © 1974 Cambridge University Press. (Received 15 January 1974) We are indebted to colleagues and students at the Graduate Aeronautical Laboratories (GALCIT) for many helpful discussions, suggestions and ideas, as well as assistance with various aspects of the experiments. Some of the shadow pictures are from Rebollo (1973). A short account of this work (Brown & Roshko 1971) was given at the AGARD Conference on Turbulent Shear Flows. The work was made possible by the generous support of the Office of Naval Research under contract N00014-67-A-0094-0001.
Issue or Number:4
Record Number:CaltechAUTHORS:BROjfm74
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ID Code:10104
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Deposited On:13 Apr 2008
Last Modified:08 Nov 2021 21:05

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