Laboratory investigation of lateral dispersion within dense arrays of randomly distributed cylinders at transitional Reynolds number
Name
Tanino Nepf Phys Fluids 2009.pdf
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Author(s)
Nepf, Heidi
Tanino, Yukie
Date Issued
April 2009
Journal
Physics of Fluids
Publisher
American Institute of Physics
Citation
Tanino, Yukie, and Heidi M. Nepf. “Laboratory investigation of lateral dispersion within dense arrays of randomly distributed cylinders at transitional Reynolds number.” Physics of Fluids 21.4 (2009): 046603-10. © 2009 American Institute of Physics.
Version
Final published version
Abstract
Relative (effective) lateral dispersion of a passive solute was examined at transitional Reynolds numbers within a two-dimensional array of randomly distributed circular cylinders of uniform diameter d. The present work focuses on dense arrays, for which previously developed theory [ Y. Tanino and H. M. Nepf, J. Fluid Mech. 600, 339 (2008) ] implies that the asymptotic (long-time/long-distance) dispersion coefficient, when normalized by the mean interstitial fluid velocity, 〈math〉, and d, will only exhibit a weak dependence on Reynolds number, Red ≡ 〈math〉d/ν, where ν is the kinematic viscosity. However, the advective distance required to reach asymptotic dispersion is expected to be controlled by pore-scale mixing, which is strongly Red-dependent prior to the onset of full turbulence. Laser-induced fluorescence was used to measure the time-averaged lateral concentration profiles of solute released continuously from a point source in arrays of solid volume fraction ϕ = 0.20 and 0.35 at Red = 48–120. Results are compared to previous measurements at higher Red. Lateral dispersion reaches the same rate as asymptotic dispersion in fully turbulent flow at x ≈ 154d at (ϕ,Red) = (0.20,110–120) and at x ≈ 87d at (ϕ,Red) = (0.35,300–390). In contrast, dispersion does not reach the fully turbulent flow limit at Red<100 within the range of x considered. Also, concentration profiles deviate further from a Gaussian distribution at ϕ = 0.35 than at 0.20 for similar Red and xϕ/d. From these observations, it can be inferred that the pre-asymptotic regime extends farther downstream, in terms of the number of cylinders spanned, at lower Red and at larger ϕ.
MIT Department
Massachusetts Institute of Technology. Department of Civil and Environmental Engineering
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DOI of Published Version
https://doi.org/10.1063/1.3119862
