Roughness Effects on Scalar Transport
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Authors
Hantsis, Zvi
Piomelli, Ugo
Date
2020-11-18
Type
journal article
Language
en
Keyword
Boundary layers , Turbulence , Immersed boundary methods
Alternative Title
Abstract
We have studied the transport of a passive scalar for passive scalar with Prandtl numbers near unity in a plane channel with rough walls. The study was carried out by direct numerical simulations of the Navier-Stokes equations; an Immersed Boundary Method was used to model the roughness. The well-known departure from the Reynolds Analogy, which postulates similarity between the statistics of the scalar and the velocity, is verified. Townsend's similarity, suggesting the smooth-wall and rough-wall statistics collapse away from the wall is confirmed. The role of the form-induced production was a focus of this work. Additional form-induced contributions appear in the Reynolds-stress and scalar-variance budgets due to the roughness; they were quantified and compared between passive scalar and momentum. The form-induced production is more significant for the scalar variance than for the streamwise Reynolds stress, and could be the cause of the reduced damping of scalar fluctuations by the roughness. The sheltering caused by tall roughness elements decreases the mean gradients significantly but, in the case of the scalar, is countered by diffusion, so that the form-induced production is larger for the scalar variance. The implications of this finding are discussed.
Description
This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in Physical Review Fluids, copyright © American Physical Society after peer review. The final edited and published work is available at https://doi.org/10.1103/PhysRevFluids.5.114607.
Citation
Hantsis, Z.; Piomelli, U. Roughness Effects on Scalar Transport. Physical review fluids 2020, 5 (11). https://doi.org/10.1103/PhysRevFluids.5.114607.
Publisher
American Physical Society