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Small-scale dissipation in binary-species, thermodynamically supercritical, transitional mixing layers

Okong'o, Nora and Bellan, Josette (2010) Small-scale dissipation in binary-species, thermodynamically supercritical, transitional mixing layers. Computers & Fluids, 39 (7). pp. 1112-1124. ISSN 0045-7930.

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The irreversible entropy production (i.e. the dissipation) has three distinct modes due to viscous, heat and species-mass fluxes. Computations of the dissipation and its modes are conducted using transitional states obtained from Direct Numerical Simulations (DNS) of O_2/H_2 and C_7H_(16)/N_2 temporal mixing layers at thermodynamically supercritical pressure. A non-dimensionalization of the mathematical expression for each dissipation mode is first performed and representative reference values computed using the DNS database are utilized to highlight the order of magnitude of each mode and their relative importance. For more quantitative results, the importance of each dissipative mode is assessed both at the DNS scale and at scales determined by filter sizes from four to sixteen times the DNS grid spacing. The subgrid-scale (SGS) dissipation is computed by subtracting the filtered-field dissipation from the DNS-field dissipation. For each species system, three layers are considered having different initial Reynolds number and perturbation wavelength. For all layers, it is found that the species-mass flux contribution dominates both the DNS and SGS dissipation due to high density-gradient-magnitude (HDGM) regions which are a distinctive physical aspect of these layers. Backscatter, indicated by regions of negative SGS dissipation, is found in a substantial portion (15–60%) of the domain, and decreases only slightly with increasing filter width. Regions of the most intense negative and positive SGS dissipation strongly correlate with the HDGM regions. On a domain-average basis, the proportional contribution of each dissipation mode to the total is similar at the DNS and SGS scales, indicating scale-similarity. The proportion of the species-mass dissipation mode to the total is remarkably similar in value across all simulations whether at the DNS or SGS scale. For each mode and the total, the SGS contribution to the DNS-field dissipation is only species-system and filter-size dependent but nearly independent of the initial Reynolds number and perturbation wavelength. The SGS contribution is smaller for O_2/H_2 layers than for C_7H_(16)/N_2 ones, but increases more rapidly with increasing filter width. The implications of these results for Larger Eddy Simulation modeling are discussed.

Item Type:Article
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Bellan, Josette0000-0001-9218-7017
Additional Information:© 2010 Elsevier Ltd. Received 17 April 2009, Revised 27 January 2010, Accepted 1 February 2010, Available online 11 February 2010.
Subject Keywords:Supercritical mixing layers; Dissipation
Issue or Number:7
Record Number:CaltechAUTHORS:20171023-161319825
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Official Citation:Nora Okong’o, Josette Bellan, Small-scale dissipation in binary-species, thermodynamically supercritical, transitional mixing layers, In Computers & Fluids, Volume 39, Issue 7, 2010, Pages 1112-1124, ISSN 0045-7930, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:82602
Deposited By: Tony Diaz
Deposited On:24 Oct 2017 20:36
Last Modified:09 Mar 2020 13:18

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