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Subgrid-scale models and large-eddy simulation of oxygen stream disintegration and mixing with a hydrogen or helium stream at supercritical pressure

Taşkinoğlu, Ezgi S. and Bellan, Josette (2011) Subgrid-scale models and large-eddy simulation of oxygen stream disintegration and mixing with a hydrogen or helium stream at supercritical pressure. Journal of Fluid Mechanics, 679 . pp. 156-193. ISSN 0022-1120.

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For flows at supercritical pressure, p, the large-eddy simulation (LES) equations consist of the differential conservation equations coupled with a real-gas equation of state, and the equations utilize transport properties depending on the thermodynamic variables. Compared to previous LES models, the differential equations contain not only the subgrid-scale (SGS) fluxes but also new SGS terms, each denoted as a ‘correction’. These additional terms, typically assumed null for atmospheric pressure flows, stem from filtering the differential governing equations and represent differences, other than contributed by the convection terms, between a filtered term and the same term computed as a function of the filtered flow field. In particular, the energy equation contains a heat-flux correction (q-correction) which is the difference between the filtered divergence of the molecular heat flux and the divergence of the molecular heat flux computed as a function of the filtered flow field. We revisit here a previous a priori study where we only had partial success in modelling the q-correction term and show that success can be achieved using a different modelling approach. This a priori analysis, based on a temporal mixing-layer direct numerical simulation database, shows that the focus in modelling the q-correction should be on reconstructing the primitive variable gradients rather than their coefficients, and proposes the approximate deconvolution model (ADM) as an effective means of flow field reconstruction for LES molecular heat-flux calculation. Furthermore, an a posteriori study is conducted for temporal mixing layers initially containing oxygen (O) in the lower stream and hydrogen (H) or helium (He) in the upper stream to examine the benefit of the new model. Results show that for any LES including SGS-flux models (constant-coefficient gradient or scale-similarity models; dynamic-coefficient Smagorinsky/Yoshizawa or mixed Smagorinsky/Yoshizawa/gradient models), the inclusion of the q-correction in LES leads to the theoretical maximum reduction of the SGS molecular heat-flux difference; the remaining error in modelling this new subgrid term is thus irreducible. The impact of the q-correction model first on the molecular heat flux and then on the mean, fluctuations, second-order correlations and spatial distribution of dependent variables is also demonstrated. Discussions on the utilization of the models in general LES are presented.

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Additional Information:© 2011 Cambridge University Press. Received 21 May 2010; revised 8 March 2011; accepted 10 March 2011; first published online 11 May 2011. This work was conducted at the Jet Propulsion Laboratory (JPL), California Institute of Technology (Caltech) and sponsored by the Air Force Office of Scientific Research from the program of Dr Julian Tishkoff under an agreement with the National Aeronautics and Space Administration, and of an AFOSR Grant to Caltech under the programs of Drs Mitat Birkan, Douglas Talley (of Edwards Air Force Research Laboratories – AFRL), Timothy Edwards and Campbell Carter (both of Wright Patterson AFRL). We would like to thank Dr Nora Okong’o for interesting discussions. The computational resources were provided by the JPL and NASA AMES Supercomputing Center.
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Air Force Office of Scientific Research (AFOSR)UNSPECIFIED
Subject Keywords:turbulence modelling; turbulence simulation; turbulent mixing
Record Number:CaltechAUTHORS:20110801-094730278
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24607
Deposited By: Tony Diaz
Deposited On:06 Oct 2011 20:26
Last Modified:23 Aug 2016 00:03

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