Rough-wall turbulence in minimal flow units with rod-roughened walls

2020 ◽  
Vol 32 (11) ◽  
pp. 115120
Author(s):  
Bo-Yuan Zhang ◽  
Wei-Xi Huang ◽  
Chun-Xiao Xu
Keyword(s):  
Wall Turbulence ◽  
Rough Wall ◽  
Minimal Flow ◽  
Flow Units

On near-wall turbulence in minimal flow units

2017 ◽  
Vol 65 ◽  
pp. 192-199 ◽  
Author(s):  
Guang Yin ◽  
Wei-Xi Huang ◽  
Chun-Xiao Xu
Keyword(s):  
Wall Turbulence ◽  
Minimal Flow ◽  
Flow Units ◽  
Near Wall Turbulence ◽  
Near Wall

Modelling smooth- and transitionally rough-wall turbulent channel flow by leveraging inner–outer interactions and principal component analysis

2019 ◽  
Vol 863 ◽  
pp. 407-453 ◽  
Author(s):  
Sicong Wu ◽  
Kenneth T. Christensen ◽  
Carlos Pantano
Keyword(s):  
Principal Component Analysis ◽  
Outer Layer ◽  
Principal Component ◽  
Turbulent Channel Flow ◽  
Reynolds Numbers ◽  
Wall Turbulence ◽  
Rough Wall ◽  
Smooth Wall ◽  
Wall Flow ◽  
Near Wall

Direct numerical simulations (DNS) of turbulent channel flow over rough surfaces, formed from hexagonally packed arrays of hemispheres on both walls, were performed at friction Reynolds numbers $Re_{\unicode[STIX]{x1D70F}}=200$, $400$ and $600$. The inner normalized roughness height $k^{+}=20$ was maintained for all Reynolds numbers, meaning all flows were classified as transitionally rough. The spacing between hemispheres was varied within $d/k=2$–$4$. The statistical properties of the rough-wall flows were contrasted against a complementary smooth-wall DNS at $Re_{\unicode[STIX]{x1D70F}}=400$ and literature data at $Re_{\unicode[STIX]{x1D70F}}=2003$ revealing strong modifications of the near-wall turbulence, although the outer-layer structure was found to be qualitatively consistent with smooth-wall flow. Amplitude modulation (AM) analysis was used to explore the degree of interaction between the flow in the roughness sublayer and that of the outer layer utilizing all velocity components. This analysis revealed stronger modulation effects, compared to smooth-wall flow, on the near-wall small-scale fluctuations by the larger-scale structures residing in the outer layer irrespective of roughness arrangement and Reynolds number. A predictive inner–outer model based on these interactions, and exploiting principal component analysis (PCA), was developed to predict the statistics of higher-order moments of all velocity fluctuations, thus addressing modelling of anisotropic effects introduced by roughness. The results show excellent agreement between the predicted near-wall statistics up to fourth-order moments compared to the original statistics from the DNS, which highlights the utility of the PCA-enhanced AM model in generating physics-based predictions in both smooth- and rough-wall turbulence.

Spatial structure of a turbulent boundary layer with irregular surface roughness

2010 ◽  
Vol 655 ◽  
pp. 380-418 ◽  
Author(s):  
Y. WU ◽  
K. T. CHRISTENSEN
Keyword(s):  
Spatial Structure ◽  
Outer Layer ◽  
Decomposition Analysis ◽  
Wall Turbulence ◽  
Rough Wall ◽  
Smooth Wall ◽  
Structure Of Flow ◽  
Moderate Reynolds Number ◽  
Wall Flow ◽  
The Impact

Particle image velocimetry experiments were performed to study the impact of realistic roughness on the spatial structure of wall turbulence at moderate Reynolds number. This roughness was replicated from an actual turbine blade damaged by deposition of foreign materials and its features are quite distinct from most roughness characterizations previously considered as it is highly irregular and embodies a broad range of topographical scales. The spatial structure of flow over this rough surface near the outer edge of the roughness sublayer is contrasted with that of smooth-wall flow to identify any structural modifications due to roughness. Hairpin vortex packets are observed in the outer layer of the rough-wall flow and are found to contribute heavily to the Reynolds shear stress, consistent with smooth-wall flow. While similar qualitative consistency is observed in comparisons of smooth- and rough-wall two-point correlations, some quantitative differences are also apparent. In particular, a reduction in the streamwise extent of two-point correlations of streamwise velocity is noted which could be indicative of a roughness-induced modification of outer-layer vortex organization. Proper orthogonal decomposition analysis reveals the streamwise coherence of the larger scales to be most sensitive to roughness while the spatial characteristics of the smaller scales appear relatively insensitive to such effects.

Scaling of rough-wall turbulence by the roughness height and steepness

2020 ◽  
Vol 900 ◽  
Author(s):  
Guo-Zhen Ma ◽  
Chun-Xiao Xu ◽  
Hyung Jin Sung ◽  
Wei-Xi Huang
Keyword(s):  
Roughness Height ◽  
Wall Turbulence ◽  
Rough Wall ◽  
Image Position

Abstract

Inner–outer interactions in rough-wall turbulence

2016 ◽  
Vol 17 (12) ◽  
pp. 1159-1178 ◽  
Author(s):  
D. T. Squire ◽  
W. J. Baars ◽  
N. Hutchins ◽  
I. Marusic
Keyword(s):  
Wall Turbulence ◽  
Rough Wall
Sign in / Sign up

Export Citation Format

Share Document