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Title: Turbulent shear-layer mixing: initial conditions, and direct-numerical and large-eddy simulations

Abstract

Aspects of turbulent shear-layer mixing are investigated over a range of shear-layer Reynolds numbers,$$Re_{\unicode[STIX]{x1D6FF}}=\unicode[STIX]{x0394}U\unicode[STIX]{x1D6FF}/\unicode[STIX]{x1D708}$$, based on the shear-layer free-stream velocity difference,$$\unicode[STIX]{x0394}U$$, and mixing-zone thickness,$$\unicode[STIX]{x1D6FF}$$, to probe the role of initial conditions in mixing stages and the evolution of the scalar-field probability density function (p.d.f.) and variance. Scalar transport is calculated for unity Schmidt numbers, approximating gas-phase diffusion. The study is based on direct-numerical simulation (DNS) and large-eddy simulation (LES), comparing different subgrid-scale (SGS) models for incompressible, uniform-density, temporally evolving forced shear-layer flows. Moderate-Reynolds-number DNS results help assess and validate LES SGS models in terms of scalar-spectrum and mixing estimates, as well as other metrics, to$$Re_{\unicode[STIX]{x1D6FF}}\lesssim 3.3\times 10^{4}$$. High-Reynolds-number LES investigations to$$Re_{\unicode[STIX]{x1D6FF}}\lesssim 5\times 10^{5}$$help identify flow parameters and conditions that influence the evolution of scalar variance and p.d.f., e.g. marching versus non-marching. Initial conditions that generate shear flows with different mixing behaviour elucidate flow characteristics in each flow regime and identify elements that induce p.d.f. transition and scalar-variance behaviour. P.d.f. transition is found to be largely insensitive to local flow parameters, such as$$Re_{\unicode[STIX]{x1D6FF}}$$, or a previously proposed vortex-pairing parameter based on downstream distance, or other equivalent criteria. The present study also allows a quantitative comparison of LES SGS models in moderate- and high-$$Re_{\unicode[STIX]{x1D6FF}}$$forced shear-layer flows.

Authors:
ORCiD logo; ;
Publication Date:
Research Org.:
California Institute of Technology (CalTech), Pasadena, CA (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1801108
DOE Contract Number:  
NA0002382; AC02-06CH11357
Resource Type:
Journal Article
Journal Name:
Journal of Fluid Mechanics
Additional Journal Information:
Journal Volume: 877; Journal ID: ISSN 0022-1120
Publisher:
Cambridge University Press
Country of Publication:
United States
Language:
English
Subject:
Mechanics; Physics

Citation Formats

Sharan, Nek, Matheou, Georgios, and Dimotakis, Paul E. Turbulent shear-layer mixing: initial conditions, and direct-numerical and large-eddy simulations. United States: N. p., 2019. Web. doi:10.1017/jfm.2019.591.
Sharan, Nek, Matheou, Georgios, & Dimotakis, Paul E. Turbulent shear-layer mixing: initial conditions, and direct-numerical and large-eddy simulations. United States. https://doi.org/10.1017/jfm.2019.591
Sharan, Nek, Matheou, Georgios, and Dimotakis, Paul E. Mon . "Turbulent shear-layer mixing: initial conditions, and direct-numerical and large-eddy simulations". United States. https://doi.org/10.1017/jfm.2019.591.
@article{osti_1801108,
title = {Turbulent shear-layer mixing: initial conditions, and direct-numerical and large-eddy simulations},
author = {Sharan, Nek and Matheou, Georgios and Dimotakis, Paul E.},
abstractNote = {Aspects of turbulent shear-layer mixing are investigated over a range of shear-layer Reynolds numbers,$Re_{\unicode[STIX]{x1D6FF}}=\unicode[STIX]{x0394}U\unicode[STIX]{x1D6FF}/\unicode[STIX]{x1D708}$, based on the shear-layer free-stream velocity difference,$\unicode[STIX]{x0394}U$, and mixing-zone thickness,$\unicode[STIX]{x1D6FF}$, to probe the role of initial conditions in mixing stages and the evolution of the scalar-field probability density function (p.d.f.) and variance. Scalar transport is calculated for unity Schmidt numbers, approximating gas-phase diffusion. The study is based on direct-numerical simulation (DNS) and large-eddy simulation (LES), comparing different subgrid-scale (SGS) models for incompressible, uniform-density, temporally evolving forced shear-layer flows. Moderate-Reynolds-number DNS results help assess and validate LES SGS models in terms of scalar-spectrum and mixing estimates, as well as other metrics, to$Re_{\unicode[STIX]{x1D6FF}}\lesssim 3.3\times 10^{4}$. High-Reynolds-number LES investigations to$Re_{\unicode[STIX]{x1D6FF}}\lesssim 5\times 10^{5}$help identify flow parameters and conditions that influence the evolution of scalar variance and p.d.f., e.g. marching versus non-marching. Initial conditions that generate shear flows with different mixing behaviour elucidate flow characteristics in each flow regime and identify elements that induce p.d.f. transition and scalar-variance behaviour. P.d.f. transition is found to be largely insensitive to local flow parameters, such as$Re_{\unicode[STIX]{x1D6FF}}$, or a previously proposed vortex-pairing parameter based on downstream distance, or other equivalent criteria. The present study also allows a quantitative comparison of LES SGS models in moderate- and high-$Re_{\unicode[STIX]{x1D6FF}}$forced shear-layer flows.},
doi = {10.1017/jfm.2019.591},
url = {https://www.osti.gov/biblio/1801108}, journal = {Journal of Fluid Mechanics},
issn = {0022-1120},
number = ,
volume = 877,
place = {United States},
year = {2019},
month = {8}
}

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