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Mixing at large Schmidt number in the self-similar far field of turbulent jets

Dahm, Werner J. A. and Dimotakis, Paul E. (1990) Mixing at large Schmidt number in the self-similar far field of turbulent jets. Journal of Fluid Mechanics, 217 . pp. 299-330. ISSN 0022-1120. doi:10.1017/S0022112090000738.

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We present results from an experimental investigation of turbulent transport and molecular mixing of a Sc [dbl greater-than sign] 1 conserved scalar in the fully developed self-similar far field of a steady, axisymmetric, momentum-driven, free turbulent jet issuing into a quiescent medium. Our experiments cover the axial range from the jet exit to 350 diameters downstream, and span the range of Reynolds numbers from 1500 to 20000. Flow visualizations of the scalar concentration field directly verify the presence of an underlying characteristic large-scale organization in the jet far field essentially consistent with a simplified conceptual picture proposed in an earlier study (Dahm & Dimotakis 1987). High-resolution imaging measurements of successive instantaneous scalar concentration profiles in the jet support the presence of such a large-scale organization and provide details of its implications for mixing. These results also establish the proper similarity scaling for the mean concentration in the jet far field and give the scaling constant on the jet centreline as 5.4. We also present conserved scalar concentration p.d.f.s throughout the jet far field, and introduce a chemical reaction method for measuring the p.d.f.s with potentially molecular resolution. The amount of unmixed ambient fluid that reaches the jet centreline is found to decrease with increasing Reynolds number over the range investigated. The distribution of mixed fluid compositions in the concentration p.d.f. also appears to change over this range of Reynolds numbers, indicating that some aspects of large Schmidt number mixing in the jet far field have not yet become Reynolds number independent.

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Additional Information:Copyright © 1990 Cambridge University Press. Reprinted with permission. (Received on 22 February 1988 and in revised form 12 January 1990) We would like to acknowledge valuable contributions by Dr M.M. Koochesfahani in the development of the imaging techniques, and numerous discussions with Dr J.E. Broadwell. This work was sponsored, in part, by the Gas Research Institute under Grant No. 5083-260-0878, by the Air Force Office of Scientific Research under Grant No. 83-0213 and Contract No. F49620-79-0159, and by the Energy and Environmental Research Corporation under Contract No. 8400-28.
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Deposited On:18 Jun 2008
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