Sponsor
Portland State University Faculty Developments Grant (No. FDG-FEAXYZ; Funder ID: 10.13039/100007083). Anvil platform through the allocation from the ACCESS program (No. MCH230024). National Natural Science Foundation of China (No. 12302331 Funder ID: 10.13039/501100001809). Fundamental Research Funds for the Central Universities (No. JZ2021HGTB0122; Funder ID: 10.13039/501100012226). HPC Platform of Hefei University of Technology.
Published In
Journal of Fluids Engineering
Document Type
Post-Print
Publication Date
3-2025
Subjects
Spanwise heterogeneity -- Hydrodynamics -- Mathematical models
Abstract
Spanwise heterogeneity in surface roughness generates secondary mean flows in a rough-wall turbulent boundary layer. This study investigates the influence of roughness spanwise wavelength on the arrangement of these secondary flows using direct numerical simulation (DNS). We systematically vary the spanwise wavelength, δS/δ, from ππ/16 to π2π, while maintaining constant roughness height and surface coverage density. Here, S represents the roughness spanwise wavelength, and δδ denotes the outer length scale, which in this case is the half-channel height. Secondary flows are observed in all DNS cases, but their configurations depend on the spanwise wavelength. Specifically, small wavelengths result in low-momentum pathways (LMPs) above the roughness elements, whereas large wavelengths lead to high-momentum pathways (HMPs) at these locations. To elucidate the mechanisms behind this rearrangement, we analyze the mean streamwise vorticity transport equation. The findings indicate that shear stress anisotropy induces another pair of secondary vortices above the roughness elements as the spanwise wavelength increases. Given that secondary flows are features of the mean flow, we further examine the budgets of the dispersive kinetic energy (DKE). The analyses reveal that at small spanwise wavelengths, shear production primarily generates DKE, while at large wavelengths, wake production becomes the dominant energy source. Building on these insights, we propose a refined classification for surfaces with spanwise heterogeneity.
Rights
Copyright (c) 2025 The Authors
Locate the Document
DOI
10.1115/1.4067791
Persistent Identifier
https://archives.pdx.edu/ds/psu/43560
Citation Details
Yang, X., Yang, J., Liu, L., Zhu, J., & Zhu, X. (2025). Impact of Roughness Spanwise Wavelength on Secondary Flow Rearrangement. Journal of Fluids Engineering, 1-30.
Description
Post print, No embargo per publisher
This is the author’s version of a work that was accepted for publication