Gat, Ilana and Matheou, Georgios and Chung, Daniel and Dimotakis, Paul E.
(2017)
*Incompressible variable-density turbulence in an external acceleration field.*
Journal of Fluid Mechanics, 827
.
pp. 506-535.
ISSN 0022-1120.
https://resolver.caltech.edu/CaltechAUTHORS:20170911-101013585

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## Abstract

Dynamics and mixing of a variable-density turbulent flow subject to an externally imposed acceleration field in the zero-Mach-number limit are studied in a series of direct numerical simulations. The flow configuration studied consists of alternating slabs of high- and low-density fluid in a triply periodic domain. Density ratios in the range of 1.05 ⩽ R ≡ ρ_1/ρ_2 ⩽ 10 are investigated. The flow produces temporally evolving shear layers. A perpendicular density–pressure gradient is maintained in the mean as the flow evolves, with multi-scale baroclinic torques generated in the turbulent flow that ensues. For all density ratios studied, the simulations attain Reynolds numbers at the beginning of the fully developed turbulence regime. An empirical relation for the convection velocity predicts the observed entrainment-ratio and dominant mixed-fluid composition statistics. Two mixing-layer temporal evolution regimes are identified: an initial diffusion-dominated regime with a growth rate ~t^(1/2) followed by a turbulence-dominated regime with a growth rate ~t^3. In the turbulent regime, composition probability density functions within the shear layers exhibit a slightly tilted (‘non-marching’) hump, corresponding to the most probable mole fraction. The shear layers preferentially entrain low-density fluid by volume at all density ratios, which is reflected in the mixed-fluid composition.

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Additional Information: | © 2017 Cambridge University Press. Received 1 May 2017; revised 1 May 2017; accepted 14 July 2017. Published online: 24 August 2017. The work is supported by DOE grant DE-NA0002382, the NSF Graduate Research Fellowship Program under grant DGE-1144469, the Caltech academic program, and the Caltech Northrop Chair in Aeronautics. Support was also provided by the AFOSR grant FA9550-12-1-0461, the Blue Waters Sustained-Petascale Computing Project, supported by NSF Awards OCI-0725070 and ACI-1238993, and the state of Illinois. Blue Waters is a joint effort of the University of Illinois at Urbana-Champaign and its National Center for Supercomputing Applications. Simulations performed on Blue Waters were under NSF PRAC award number ACI-1440083. Computations were also performed on the Caltech Zwicky computer cluster, supported by NSF MRI-R2 Award PHY-0060291 and by the Sherman Fairchild Foundation. The work was also supported by the Cray Trinity system of the Alliance for Computing at Extreme Scale (ACES), a partnership between Los Alamos National Laboratory and Sandia National Laboratories for the U.S. Department of Energy’s NNSA. Data storage, visualization, and post-processing were facilitated by a computer cluster integrated by D. Lang, and developed through support by NSF MRI grant EIA-0079871, AFOSR DURIP grant FA9550-10-1-0553, and support by the AFOSR and DOE grants mentioned above. We’d like to thank C. Pantano for noting an additional term in the self-similar mass conservation equation contributed by the diffusion-induced velocity (4.3). We would finally like to acknowledge discussions with D. Meiron and D. Pullin, and a collaboration in the computations with C. Ott. | ||||||||||||||||||||||||||||||

Group: | GALCIT | ||||||||||||||||||||||||||||||

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Subject Keywords: | shear layer turbulence; turbulent flows; turbulent mixing | ||||||||||||||||||||||||||||||

Record Number: | CaltechAUTHORS:20170911-101013585 | ||||||||||||||||||||||||||||||

Persistent URL: | https://resolver.caltech.edu/CaltechAUTHORS:20170911-101013585 | ||||||||||||||||||||||||||||||

Official Citation: | Gat, I., Matheou, G., Chung, D., & Dimotakis, P. (2017). Incompressible variable-density turbulence in an external acceleration field. Journal of Fluid Mechanics, 827, 506-535. doi:10.1017/jfm.2017.490 | ||||||||||||||||||||||||||||||

Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. | ||||||||||||||||||||||||||||||

ID Code: | 81287 | ||||||||||||||||||||||||||||||

Collection: | CaltechAUTHORS | ||||||||||||||||||||||||||||||

Deposited By: | Tony Diaz | ||||||||||||||||||||||||||||||

Deposited On: | 11 Sep 2017 17:40 | ||||||||||||||||||||||||||||||

Last Modified: | 03 Oct 2019 18:41 |

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