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

Journal Article · Mon Aug 19 00:00:00 EDT 2019 · Journal of Fluid Mechanics

DOI:https://doi.org/10.1017/jfm.2019.591· OSTI ID:1801108

Sharan, Nek ; Matheou, Georgios; Dimotakis, Paul E.

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.

• Research Organization: California Institute of Technology (CalTech), Pasadena, CA (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• DOE Contract Number: NA0002382; AC02-06CH11357
• OSTI ID: 1801108
• Journal Information: Journal of Fluid Mechanics, Vol. 877; ISSN 0022-1120
• Publisher: Cambridge University Press
• Country of Publication: United States
• Language: English

Related Subjects

Mechanics
Physics