Incompressible variabledensity turbulence in an external acceleration field
Dynamics and mixing of a variabledensity turbulent flow subject to an externally imposed acceleration field in the zeroMachnumber limit are studied in a series of direct numerical simulations. The flow configuration studied consists of alternating slabs of high and lowdensity fluid in a triply periodic domain. Density ratios in the range of$$1.05\leqslant R\equiv \unicode[STIX]{x1D70C}_{1}/\unicode[STIX]{x1D70C}_{2}\leqslant 10$$are investigated. The flow produces temporally evolving shear layers. A perpendicular density–pressure gradient is maintained in the mean as the flow evolves, with multiscale 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 entrainmentratio and dominant mixedfluid composition statistics. Two mixinglayer temporal evolution regimes are identified: an initial diffusiondominated regime with a growth rate$${\sim}t^{1/2}$$followed by a turbulencedominated regime with a growth rate$${\sim}t^{3}$$. In the turbulent regime, composition probability density functions within the shear layers exhibit a slightly tilted (‘nonmarching’) hump, corresponding to the most probable mole fraction. In conclusion, the shear layers preferentially entrain lowdensity fluid by volume at all density ratios, which is reflected in the mixedfluid composition.
 Authors:

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 California Inst. of Technology (CalTech), Pasadena, CA (United States)
 California Inst. of Technology (CalTech), Pasadena, CA (United States); Univ. of Connecticut, Storrs, CT (United States)
 Univ. of Melbourne, Victoria (Australia)
 Publication Date:
 Grant/Contract Number:
 NA0002382
 Type:
 Accepted Manuscript
 Journal Name:
 Journal of Fluid Mechanics
 Additional Journal Information:
 Journal Volume: 827; Journal ID: ISSN 00221120
 Publisher:
 Cambridge University Press
 Research Org:
 California Inst. of Technology (CalTech), Pasadena, CA (United States)
 Sponsoring Org:
 USDOE National Nuclear Security Administration (NNSA), Office of Defense Programs (DP) (NA10)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 97 MATHEMATICS AND COMPUTING
 OSTI Identifier:
 1398345
Gat, Ilana, Matheou, Georgios, Chung, Daniel, and Dimotakis, Paul E. Incompressible variabledensity turbulence in an external acceleration field. United States: N. p.,
Web. doi:10.1017/jfm.2017.490.
Gat, Ilana, Matheou, Georgios, Chung, Daniel, & Dimotakis, Paul E. Incompressible variabledensity turbulence in an external acceleration field. United States. doi:10.1017/jfm.2017.490.
Gat, Ilana, Matheou, Georgios, Chung, Daniel, and Dimotakis, Paul E. 2017.
"Incompressible variabledensity turbulence in an external acceleration field". United States.
doi:10.1017/jfm.2017.490. https://www.osti.gov/servlets/purl/1398345.
@article{osti_1398345,
title = {Incompressible variabledensity turbulence in an external acceleration field},
author = {Gat, Ilana and Matheou, Georgios and Chung, Daniel and Dimotakis, Paul E.},
abstractNote = {Dynamics and mixing of a variabledensity turbulent flow subject to an externally imposed acceleration field in the zeroMachnumber limit are studied in a series of direct numerical simulations. The flow configuration studied consists of alternating slabs of high and lowdensity fluid in a triply periodic domain. Density ratios in the range of$1.05\leqslant R\equiv \unicode[STIX]{x1D70C}_{1}/\unicode[STIX]{x1D70C}_{2}\leqslant 10$are investigated. The flow produces temporally evolving shear layers. A perpendicular density–pressure gradient is maintained in the mean as the flow evolves, with multiscale 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 entrainmentratio and dominant mixedfluid composition statistics. Two mixinglayer temporal evolution regimes are identified: an initial diffusiondominated regime with a growth rate${\sim}t^{1/2}$followed by a turbulencedominated regime with a growth rate${\sim}t^{3}$. In the turbulent regime, composition probability density functions within the shear layers exhibit a slightly tilted (‘nonmarching’) hump, corresponding to the most probable mole fraction. In conclusion, the shear layers preferentially entrain lowdensity fluid by volume at all density ratios, which is reflected in the mixedfluid composition.},
doi = {10.1017/jfm.2017.490},
journal = {Journal of Fluid Mechanics},
number = ,
volume = 827,
place = {United States},
year = {2017},
month = {8}
}