Title: Experimental study of vorticity-strain rate interaction in turbulent partially-premixed jet flames using tomographic particle image velocimetry

Abstract

In turbulent flows, the interaction between vorticity, ω, and strain rate, s, is considered a primary mechanism for the transfer of energy from large to small scales through vortex stretching. The ω-s coupling in turbulent jet flames is investigated using tomographic particle image velocimetry (TPIV). TPIV provides a direct measurement of the three-dimensional velocity field from which ω and s are determined. The effects of combustion and mean shear on the ω-s interaction are investigated in turbulent partially premixed methane/air jet flames with high and low probabilities of localized extinction as well as in a non-reacting isothermal air jet with Reynolds number of approximately 13,000. Results show that combustion causes structures of high vorticity and strain rate to agglomerate in highly correlated, elongated layers that span the height of the probe volume. In the non-reacting jet, these structures have a more varied morphology, greater fragmentation, and are not as well correlated. The enhanced spatiotemporal correlation of vorticity and strain rate in the stable flame results in stronger ω-s interaction characterized by increased enstrophy and strain-rate production rates via vortex stretching and straining, respectively. The probability of preferential local alignment between ω and the eigenvector of the intermediate principal strain rate,more » s₂, which is intrinsic to the ω-s coupling in turbulent flows, is larger in the flames and increases with the flame stability. The larger mean shear in the flame imposes a preferential orientation of ω and s₂ tangential to the shear layer. The extensive and compressive principal strain rates, s₁ and s₃, respectively, are preferentially oriented at approximately 45° with respect to the jet axis. As a result, the production rates of strain and vorticity tend to be dominated by instances in which ω is parallel to the s₁¯-s₂¯ plane and orthogonal to s₃¯.« less

Authors:

Coriton, Bruno ^[1]; Frank, Jonathan H. ^[1]

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+ Show Author Affiliations

1. Sandia National Laboratories (SNL-CA), Livermore, CA (United States)

Publication Date:

Tue Feb 16 00:00:00 EST 2016

Research Org.:

Sandia National Lab. (SNL-CA), Livermore, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1243352

Alternate Identifier(s):

OSTI ID: 1238079

Report Number(s):

SAND-2016-1375J
Journal ID: ISSN 1070-6631; PHFLE6; 619362

Grant/Contract Number:  

AC04-94AL85000; AC04-94-AL85000

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Fluids

Additional Journal Information:

Journal Volume: 28; Journal Issue: 2; Journal ID: ISSN 1070-6631

Publisher:

American Institute of Physics

Country of Publication:

United States

Language:

English

Subject:

42 ENGINEERING; flames; eigenvalues; rotating flows; turbulent flows; combustion