Aerodynamic Properties of Rough Surfaces with High Aspect-Ratio Roughness Elements: Effect of Aspect Ratio and Arrangements

Jasim Sadique, Xiang Yang, Charles Meneveau, Rajat Mittal

    Research output: Contribution to journalArticle

    13 Citations (Scopus)

    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 languageEnglish (US)
    Pages (from-to)203-224
    Number of pages22
    JournalBoundary-Layer Meteorology
    Volume163
    Issue number2
    DOIs
    StatePublished - May 1 2017

    Fingerprint

    aerodynamics
    roughness
    turbulent boundary layer
    large eddy simulation
    effect
    velocity profile
    turbulent flow
    friction
    plateau
    fluid
    prediction

    All Science Journal Classification (ASJC) codes

    • Atmospheric Science

    Cite this

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    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.",
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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 journalArticle

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    AU - Sadique, Jasim

    AU - Yang, Xiang

    AU - Meneveau, Charles

    AU - Mittal, Rajat

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