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Direct numerical simulation of a transitional supercritical binary mixing layer: heptane and nitrogen

Okong'o, Nora A. and Bellan, Josette (2002) Direct numerical simulation of a transitional supercritical binary mixing layer: heptane and nitrogen. Journal of Fluid Mechanics, 464 . pp. 1-34. ISSN 0022-1120. http://resolver.caltech.edu/CaltechAUTHORS:20171024-081326190

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Abstract

Direct numerical simulations (DNS) of a supercritical temporal mixing layer are conducted for the purpose of exploring the characteristics of high-pressure transitional mixing behaviour. The conservation equations are formulated according to fluctuation-dissipation (FD) theory, which is consistent with non-equilibrium thermodynamics and converges to kinetic theory in the low-pressure limit. According to FD theory, complementing the low-pressure typical transport properties (viscosity, diffusivity and thermal conductivity), the thermal diffusion factor is an additional transport property which may play an increasingly important role with increasing pressure. The Peng–Robinson equation of state with appropriate mixing rules is coupled to the dynamic conservation equations to obtain a closed system. The boundary conditions are periodic in the streamwise and spanwise directions, and of non-reflecting outflow type in the cross-stream direction. Due to the strong density stratification, the layer is considerably more difficult to entrain than equivalent gaseous or droplet-laden layers, and exhibits regions of high density gradient magnitude that become very convoluted at the transitional state. Conditional averages demonstrate that these regions contain predominantly the higher-density, entrained fluid, with small amounts of the lighter, entraining fluid, and that in these regions the mixing is hindered by the thermodynamic properties of the fluids. During the entire evolution of the layer, the dissipation is overwhelmingly due to species mass flux followed by heat flux effects with minimal viscous contribution, and there is a considerable amount of backscatter in the flow. Most of the species mass flux dissipation is due to the molecular diffusion term with significant contributions from the cross-term proportional to molecular and thermal diffusion. These results indicate that turbulence models for supercritical fluids should primarily focus on duplicating the species mass flux rather than the typical momentum flux, which constitutes the governing dissipation in atmospheric mixing layers. Examination of the passive-scalar probability density functions (PDFs) indicates that neither the Gaussian, nor the beta PDFs are able to approximate the evolution of the DNS-extracted PDF from its inception through transition. Furthermore, the temperature–species PDFs are well correlated, meaning that their joint PDF is not properly approximated by the product of their marginal PDFs; this indicates that the traditional reactive flow modelling based on replacing the joint PDF representing the reaction rate by the product of the marginal PDFs is not appropriate. Finally, the subgrid-scale temperature–species PDFs are also well correlated, and the species PDF exhibits important departures from the Gaussian. These results suggest that classic PDFs used in atmospheric pressure flows would not capture the physics of this supercritical mixing layer, either in an assumed PDF model at the larger scale, or at the subgrid scale.


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URLURL TypeDescription
https://doi.org/10.1017/S0022112002008480DOIArticle
https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/direct-numerical-simulation-of-a-transitional-supercritical-binary-mixing-layer-heptane-and-nitrogen/0A656816A5A43CFE4635EDDD046ED62FPublisherArticle
Additional Information:© 2002 Cambridge University Press. Received 25 September 2000 and in revised form 10 January 2002. Published online: 21 August 2002. This research was conducted at the Jet Propulsion Laboratory (JPL), California Institute of Technology. Joint sponsorship was provided by the Air Force Office of Scientific Research with Dr Julian Tishkoff serving as contract monitor and by the Army Research Office with Dr David Mann as technical contract monitor, through interagency agreements with the National Space and Aeronautics Administration (NASA). Computational resources were provided by the supercomputing facility at JPL. The authors wish to thank Dr Mark Carpenter of NASA Langley Research Center and Dr Kenneth Harstad of JPL for helpful discussions.
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Funding AgencyGrant Number
NASA/JPL/CaltechUNSPECIFIED
Air Force Office of Scientific Research (AFOSR)UNSPECIFIED
Army Research Office (ARO)UNSPECIFIED
Record Number:CaltechAUTHORS:20171024-081326190
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20171024-081326190
Official Citation:OKONG'O, N., & BELLAN, J. (2002). Direct numerical simulation of a transitional supercritical binary mixing layer: Heptane and nitrogen. Journal of Fluid Mechanics, 464, 1-34. doi:10.1017/S0022112002008480
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:82611
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:24 Oct 2017 20:16
Last Modified:24 Oct 2017 20:17

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