Topographical effects of roughness on turbulence statistics in roughness sublayer

J. Yuan and M. Aghaei Jouybari
Phys. Rev. Fluids 3, 114603 – Published 9 November 2018

Abstract

Single-point turbulence statistics are compared in the roughness sublayer (RSL) of turbulent open-channel flows over smooth wall and wall roughness with different textures using direct numerical simulations (DNS). The goal is to identify how the range of scales contained in a roughness topography affects the drag generation, momentum transfer, and energy balance. The presence of large surface wavelengths is shown to reduce the overall surface slope, leading to a sparser distribution of roughness-wake regions. This may provide a physical explanation why a wider scale surface tends to produce lower friction coefficient and higher Reynolds stress anisotropy as observed previously. In addition, despite recent observations of negligible form-induced turbulent kinetic energy (TKE) productions over narrow-scale surface such as sand grains and gravel bed, it is shown that these productions can be significant over a multiscale surface. We also identify several factors crucial for these productions; they include the roughness drag coefficient, the roughness geometry function, and both micro- and macroscopic surface scales.

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  • Received 4 February 2018

DOI:https://doi.org/10.1103/PhysRevFluids.3.114603

©2018 American Physical Society

Physics Subject Headings (PhySH)

Fluid Dynamics

Authors & Affiliations

J. Yuan* and M. Aghaei Jouybari

  • Department of Mechanical Engineering, Michigan State University, East Lansing, Michigan 48824, USA

  • *junlin@egr.msu.edu

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Issue

Vol. 3, Iss. 11 — November 2018

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