TY - JOUR
T1 - Aerodynamic Properties of Rough Surfaces with High Aspect-Ratio Roughness Elements
T2 - Effect of Aspect Ratio and Arrangements
AU - Sadique, Jasim
AU - Yang, Xiang I.A.
AU - Meneveau, Charles
AU - Mittal, Rajat
N1 - Funding Information:
The authors gratefully acknowledge the Office of Naval Research for financial and computational resources, the Maryland Advanced Research Computing Center (MARCC) and the National Science Foundation's Extreme Science and Engineering Discovery Environment, (XSEDE) (Towns et al. 2014 ), which is supported by National Science Foundation grant number ACI-1053575, for computational resources.
Publisher Copyright:
© 2016, Springer Science+Business Media Dordrecht.
PY - 2017/5/1
Y1 - 2017/5/1
N2 - We examine the effect of varying roughness-element aspect ratio on the mean velocity distributions of turbulent flow over arrays of rectangular-prism-shaped elements. Large-eddy simulations (LES) in conjunction with a sharp-interface immersed boundary method are used to simulate spatially-growing turbulent boundary layers over these rough surfaces. Arrays of aligned and staggered rectangular roughness elements with aspect ratio >1 are considered. First the temporally- and spatially-averaged velocity profiles are used to illustrate the aspect-ratio effects. For aligned prisms, the roughness length (zo) and the friction velocity (u∗) increase initially with an increase in the roughness-element aspect ratio, until the values reach a plateau at a particular aspect ratio. The exact value of this aspect ratio depends on the coverage density. Further increase in the aspect ratio changes neither zo, u∗ nor the bulk flow above the roughness elements. For the staggered cases, zo and u∗ continue to increase for the surface coverage density and the aspect ratios investigated. To model the flow response to variations in roughness aspect ratio, we turn to a previously developed phenomenological volumetric sheltering model (Yang et al., in J Fluid Mech 789:127–165, 2016), which was intended for low to moderate aspect-ratio roughness elements. Here, we extend this model to account for high aspect-ratio roughness elements. We find that for aligned cases, the model predicts strong mutual sheltering among the roughness elements, while the effect is much weaker for staggered cases. The model-predicted zo and u∗ agree well with the LES results. Results show that the model, which takes explicit account of the mutual sheltering effects, provides a rapid and reliable prediction method of roughness effects in turbulent boundary-layer flows over arrays of rectangular-prism roughness elements.
AB - We examine the effect of varying roughness-element aspect ratio on the mean velocity distributions of turbulent flow over arrays of rectangular-prism-shaped elements. Large-eddy simulations (LES) in conjunction with a sharp-interface immersed boundary method are used to simulate spatially-growing turbulent boundary layers over these rough surfaces. Arrays of aligned and staggered rectangular roughness elements with aspect ratio >1 are considered. First the temporally- and spatially-averaged velocity profiles are used to illustrate the aspect-ratio effects. For aligned prisms, the roughness length (zo) and the friction velocity (u∗) increase initially with an increase in the roughness-element aspect ratio, until the values reach a plateau at a particular aspect ratio. The exact value of this aspect ratio depends on the coverage density. Further increase in the aspect ratio changes neither zo, u∗ nor the bulk flow above the roughness elements. For the staggered cases, zo and u∗ continue to increase for the surface coverage density and the aspect ratios investigated. To model the flow response to variations in roughness aspect ratio, we turn to a previously developed phenomenological volumetric sheltering model (Yang et al., in J Fluid Mech 789:127–165, 2016), which was intended for low to moderate aspect-ratio roughness elements. Here, we extend this model to account for high aspect-ratio roughness elements. We find that for aligned cases, the model predicts strong mutual sheltering among the roughness elements, while the effect is much weaker for staggered cases. The model-predicted zo and u∗ agree well with the LES results. Results show that the model, which takes explicit account of the mutual sheltering effects, provides a rapid and reliable prediction method of roughness effects in turbulent boundary-layer flows over arrays of rectangular-prism roughness elements.
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U2 - 10.1007/s10546-016-0222-1
DO - 10.1007/s10546-016-0222-1
M3 - Article
AN - SCOPUS:85001133159
VL - 163
SP - 203
EP - 224
JO - Boundary-Layer Meteorology
JF - Boundary-Layer Meteorology
SN - 0006-8314
IS - 2
ER -