Abstract
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.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 203-224 |
| Number of pages | 22 |
| Journal | Boundary-Layer Meteorology |
| Volume | 163 |
| Issue number | 2 |
| DOIs | |
| State | Published - May 1 2017 |
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All Science Journal Classification (ASJC) codes
- Atmospheric Science
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Aerodynamic Properties of Rough Surfaces with High Aspect-Ratio Roughness Elements : Effect of Aspect Ratio and Arrangements. / Sadique, Jasim; Yang, Xiang; Meneveau, Charles; Mittal, Rajat.
In: Boundary-Layer Meteorology, Vol. 163, No. 2, 01.05.2017, p. 203-224.Research output: Contribution to journal › Article
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
AU - Meneveau, Charles
AU - Mittal, Rajat
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 -