TY - JOUR
T1 - Characterization of hydrodynamic and thermal properties of anisotropic irregular roughness
AU - Yang, Jiasheng
AU - Stroh, Alexander
AU - Bagheri, Shervin
AU - Frohnapfel, Bettina
AU - Forooghi, Pourya
N1 - Publisher Copyright:
© 2025
PY - 2025/12
Y1 - 2025/12
N2 - Rough surfaces are prevalent in flow-related applications due to surface degradation. The roughness topography can alter the surface skin friction and heat transfer in turbulent flows. Depending on the different mechanism of the roughness formation process, the roughness topography may exhibit anisotropic properties. The present work aims to shed light on the effect of roughness anisotropy on skin friction and heat transfer by systematically varying roughness properties in different directions and across various scales. To this end, irregular anisotropic rough surfaces are generated based on 2-D power spectrum (PS). The surfaces are generated with Gaussian height probability density functions (PDF) and with either matched surface anisotropy ratios (SAR=LxCorr/LzCorr) or effective slope ratios (ESR=ESx/ESz). By adjusting the 2-D PS, the degree of anisotropy is varied at different wavenumbers, some surfaces are more anisotropic at large scales andsome at small scales. Direct numerical simulations are performed to study turbulent flow over these anisotropic rough surfaces at Reτ=500, Pr=0.71. The results demonstrate that the roughness anisotropy play a pivotal role in influencing both skin friction and heat transfer of the rough surface, leading to alterations of up to more than 50% in the roughness function ΔU+ and the temperature roughness function ΔΘ+. Detailed analysis indicates that commonly used parameters, SAR or ESR alone, may not be the most appropriate predictive quantities to characterize the effects of anisotropic irregular roughness. In light of this, we introduce a new roughness topographical parameter ηSA= ESR/SAR that successfully correlates with the observed anisotropic effect. The suitability of this new parameter is assessed through comprehensive analysis of both the current dataset and the anisotropic roughness from literature.
AB - Rough surfaces are prevalent in flow-related applications due to surface degradation. The roughness topography can alter the surface skin friction and heat transfer in turbulent flows. Depending on the different mechanism of the roughness formation process, the roughness topography may exhibit anisotropic properties. The present work aims to shed light on the effect of roughness anisotropy on skin friction and heat transfer by systematically varying roughness properties in different directions and across various scales. To this end, irregular anisotropic rough surfaces are generated based on 2-D power spectrum (PS). The surfaces are generated with Gaussian height probability density functions (PDF) and with either matched surface anisotropy ratios (SAR=LxCorr/LzCorr) or effective slope ratios (ESR=ESx/ESz). By adjusting the 2-D PS, the degree of anisotropy is varied at different wavenumbers, some surfaces are more anisotropic at large scales andsome at small scales. Direct numerical simulations are performed to study turbulent flow over these anisotropic rough surfaces at Reτ=500, Pr=0.71. The results demonstrate that the roughness anisotropy play a pivotal role in influencing both skin friction and heat transfer of the rough surface, leading to alterations of up to more than 50% in the roughness function ΔU+ and the temperature roughness function ΔΘ+. Detailed analysis indicates that commonly used parameters, SAR or ESR alone, may not be the most appropriate predictive quantities to characterize the effects of anisotropic irregular roughness. In light of this, we introduce a new roughness topographical parameter ηSA= ESR/SAR that successfully correlates with the observed anisotropic effect. The suitability of this new parameter is assessed through comprehensive analysis of both the current dataset and the anisotropic roughness from literature.
KW - Anisotropic roughness
KW - Direct numerical simulation
KW - Ice accretion
UR - http://www.scopus.com/inward/record.url?scp=105007155172&partnerID=8YFLogxK
U2 - 10.1016/j.ijheatfluidflow.2025.109888
DO - 10.1016/j.ijheatfluidflow.2025.109888
M3 - Journal article
AN - SCOPUS:105007155172
SN - 0142-727X
VL - 116
JO - International Journal of Heat and Fluid Flow
JF - International Journal of Heat and Fluid Flow
M1 - 109888
ER -