Experimental study of the fine-scale structure of conserved scalar mixing in turbulent shear flows. Part 2. Sc ≈ 1

Kenneth A. Buch, Werner Dahm

Research output: Contribution to journalArticle

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Abstract

Results are presented from an experimental study into the fine-scale structure of generic, Sc ≈ 1, dynamically passive, conserved scalar fields in turbulent shear flows. The investigation was based on highly resolved, two-dimensional imaging of laser Rayleigh scattering, with measurements obtained in the self-similar far field of an axisymmetric coflowing turbulent jet of propane issuing into air at local outer-scale Reynolds numbers Reδ ≡ uδ/v of 11000 and 14000. The resolution and signal quality of these measurements allowed direct differentiation of the scalar field data ζ(x, t) to determine the instantaneous scalar energy dissipation rate field (ReSc)-1▽ζ·▽ζ(X, t). Results show that, as for large-Sc scalars (Buch & Dahm 1996), the scalar dissipation rate field consists entirely of strained, laminar, sheet-like diffusion layers, despite the fact that at Sc ≈ 1 the scale on which these layers are folded by vorticity gradients is comparable to the layer thickness. Good agreement is found between the measured internal structure of these layers and the self-similar local solution of the scalar transport equation for a spatially uniform but time-varying strain field. The self-similar distribution of dissipation layer thicknesses shows that the ratio of maximum to minimum thicknesses is only 3 at these conditions. The local dissipation layer thickness is related to the local outer scale as λD/δ ≡ ΛReδ -3/4 Sc-1/2, with the average thickness found to be <Λ> = 11.2, with both the largest and smallest layer thicknesses following Kolmogorov (Reδ -3/4) scaling.

Original languageEnglish (US)
Pages (from-to)1-29
Number of pages29
JournalJournal of Fluid Mechanics
Volume364
StatePublished - Jun 10 1998
Externally publishedYes

Fingerprint

Shear flow
shear flow
scalars
Rayleigh scattering
Vorticity
Propane
Energy dissipation
Reynolds number
dissipation
Imaging techniques
Lasers
Air
turbulent jets
propane
vorticity
far fields
energy dissipation
scaling
gradients
air

ASJC Scopus subject areas

  • Computational Mechanics
  • Mechanics of Materials
  • Physics and Astronomy(all)
  • Condensed Matter Physics

Cite this

Experimental study of the fine-scale structure of conserved scalar mixing in turbulent shear flows. Part 2. Sc ≈ 1. / Buch, Kenneth A.; Dahm, Werner.

In: Journal of Fluid Mechanics, Vol. 364, 10.06.1998, p. 1-29.

Research output: Contribution to journalArticle

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