Turbulent dispersion of a passive scalar in a smooth-wall turbulent boundary layer

The scalar dispersion of a ground-level point-source plume in a smooth-wall turbulent boundary layer is experimentally investigated using simultaneous particle image velocimetry and planar laser-induced fluorescence techniques. In the near-source region, the viscous sublayer is observed to trap dye,...

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Bibliographic Details
Published inJournal of fluid mechanics Vol. 969
Main Authors Lim, H.D., Vanderwel, Christina
Format Journal Article
LanguageEnglish
Published Cambridge, UK Cambridge University Press 22.08.2023
Subjects
Boundary layers
Boussinesq approximation
Boussinesq equations
Concentration gradient
Decay
Diffusion coefficients
Diffusivity
Dispersion
Dyes
Exponential functions
Far fields
Fluorescence
Fluxes
JFM Papers
Mathematical analysis
Particle image velocimetry
Planar laser induced fluorescence
Reynolds number
Schmidt number
Self-similarity
Tensors
Turbulent boundary layer
Velocity
Vertical profiles
Viscosity
Viscous sublayers
Water pollution
turbulent boundary layers
dispersion
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Summary:The scalar dispersion of a ground-level point-source plume in a smooth-wall turbulent boundary layer is experimentally investigated using simultaneous particle image velocimetry and planar laser-induced fluorescence techniques. In the near-source region, the viscous sublayer is observed to trap dye, while in the far field, the half-width, vertical profiles and peak decay of the mean concentration and concentration variance exhibit self-similar behaviour and collapse with empirical relations. Full two-dimensional maps of the turbulent scalar fluxes show a net transport direction of upward and towards the incoming flow, with the vertical profiles collapsing well with Weibull-type exponential functions and the decay of peaks following power laws. Using the first-order gradient transport to model the turbulent scalar fluxes, maps of the anisotropic turbulent diffusivity tensor and an effective turbulent diffusivity coefficient are calculated. The streamwise and wall-normal turbulent scalar fluxes are driven dominantly by the wall-normal concentration gradient. The turbulent Schmidt number, relating the turbulent diffusivity and the turbulent (eddy) viscosity calculated using the Boussinesq hypothesis, varies with wall-normal position with values of the order of unity in the logarithmic layer.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2023.562