Asymmetric secondary flows above geometrically symmetric surface roughness

Zhang，Wen1,2; Yang，Xiang I.A.3; Zhu，Xiaowei4; Wan，Minping1,2; Chen，Shiyi1,2,5

2023-08-30

10.1017/jfm.2023.590

Journal of Fluid Mechanics   Impact Factor & Quartile

0022-1120

1469-7645

The mean flow behaviour of a turbulent boundary layer over rough walls is expected to exhibit symmetries that govern the flow dynamics. In particular, when roughness elements are arranged in a spanwise symmetric manner, the mean flow above them should also exhibit spanwise symmetry. This symmetrical consideration has garnered substantial empirical support. We conduct direct numerical simulations (DNS) of flow over aligned cube arrays to test such symmetry considerations further. We vary the surface coverage density from 0.25% to 6.25%, and employ an averaging time of about 100 large-eddy turnover times, which is longer than the typical averaging time in prior DNS studies of rough-wall boundary layers. The results suggest the presence of spanwise asymmetry in the mean flow. Specifically, we observe the development of a prominent secondary vortex on one side of the cubical roughness, accompanied by a relatively smaller secondary vortex on the other side. This asymmetry becomes most pronounced when the surface coverage density is approximately 0.59%, and diminishes as the coverage density approaches either a low or a high value. We also establish that this mean flow asymmetry is robust across variations in the domain size, the initial condition, and the placement of the cubes in the spanwise direction.

turbulence simulation turbulence theory turbulent boundary layers

SCI

English

First ; Corresponding

NSFC["12102168","11988102"] ; Shenzhen Science amp; Technology Program[KQTD20180411143441009] ; Department of Science and Technology of Guangdong Province["2019B21203001","2020B1212030001"] ; NSF[500000021104]

Mechanics ; Physics

Mechanics ; Physics, Fluids & Plasmas

WOS:001060951100001

CAMBRIDGE UNIV PRESS

ENGINEERING

2-s2.0-85170644284

Scopus

1.Guangdong Provincial Key Laboratory of Turbulence Research and Applications,Department of Mechanics and Aerospace Engineering,Southern University of Science and Technology,Shenzhen,518055,China
2.Guangdong-Hong Kong-Macao Joint Laboratory for Data-Driven Fluid Mechanics and Engineering Applications,Southern University of Science and Technology,Shenzhen,518055,China
3.Mechanical Engineering,Pennsylvania State University,16802,United States
4.Department of Mechanical Engineering,Portland State University,Portland,97201,United States
5.Eastern Institute for Advanced Study,Ningbo,315200,China

Zhang，Wen,Yang，Xiang I.A.,Zhu，Xiaowei,et al. Asymmetric secondary flows above geometrically symmetric surface roughness[J]. Journal of Fluid Mechanics,2023,970.

Zhang，Wen,Yang，Xiang I.A.,Zhu，Xiaowei,Wan，Minping,&Chen，Shiyi.(2023).Asymmetric secondary flows above geometrically symmetric surface roughness.Journal of Fluid Mechanics,970.

Zhang，Wen,et al."Asymmetric secondary flows above geometrically symmetric surface roughness".Journal of Fluid Mechanics 970(2023).