Large eddy simulations and parameterisation of roughness element orientation and flow direction effects in rough wall boundary layers

Xiang Yang, C. Meneveau

    Research output: Contribution to journalArticle

    8 Citations (Scopus)

    Abstract

    We conduct a series of large eddy simulations (LES) of turbulent boundary layers over arrays of cuboidal roughness elements at arbitrary orientation angles (non-frontal orientations with the incident flow). Flow response to changing roughness orientation is systematically studied at two ground coverage densities, λp = 0.06 and 0.11. As expected, the effective roughness heights zo measured from LES are higher for λp = 0.11 than for λp = 0.06, although appreciable changes both in zo and wall shear stress (friction velocity) are observed at both ground coverage densities as the roughness orientation angle changes. This suggests the necessity of accounting for detailed rough wall topology (including more information than just λp, λf) when relating rough wall morphology to its aerodynamic properties. To this end, a recently developed analytical rough wall parameterisation is used to predict the aerodynamic properties of the simulated rough surfaces. In this rough wall model, wake interactions among roughness elements are explicitly modelled using the concept of sheltering height and exponential attenuation coefficient. As a result, the parameterisation is responsive to detailed ground roughness arrangements and flow conditions, including roughness height variations, element orientation, incident flow direction, transverse displacements, etc. Model-predicted effective roughness heights, wall stress, mean velocity at the height of the roughness, and in some cases displacement height, are compared against the LES measurements from this study as well as numerical/experiment measurements from other authors. The predictions from the model are found to agree well with the measurements both in trends and in absolute values, thus extending the applicability of the analytical rough wall model to more general surfaces than those previously tested.

    Original languageEnglish (US)
    Pages (from-to)1072-1085
    Number of pages14
    JournalJournal of Turbulence
    Volume17
    Issue number11
    DOIs
    StatePublished - Nov 1 2016

    Fingerprint

    Large eddy simulation
    large eddy simulation
    Parameterization
    parameterization
    boundary layers
    Boundary layers
    roughness
    Surface roughness
    aerodynamics
    Aerodynamics
    turbulent boundary layer
    attenuation coefficients
    wakes
    shear stress
    Shear stress
    friction
    topology
    Topology
    Friction
    trends

    All Science Journal Classification (ASJC) codes

    • Computational Mechanics
    • Condensed Matter Physics
    • Mechanics of Materials
    • Physics and Astronomy(all)

    Cite this

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    abstract = "We conduct a series of large eddy simulations (LES) of turbulent boundary layers over arrays of cuboidal roughness elements at arbitrary orientation angles (non-frontal orientations with the incident flow). Flow response to changing roughness orientation is systematically studied at two ground coverage densities, λp = 0.06 and 0.11. As expected, the effective roughness heights zo measured from LES are higher for λp = 0.11 than for λp = 0.06, although appreciable changes both in zo and wall shear stress (friction velocity) are observed at both ground coverage densities as the roughness orientation angle changes. This suggests the necessity of accounting for detailed rough wall topology (including more information than just λp, λf) when relating rough wall morphology to its aerodynamic properties. To this end, a recently developed analytical rough wall parameterisation is used to predict the aerodynamic properties of the simulated rough surfaces. In this rough wall model, wake interactions among roughness elements are explicitly modelled using the concept of sheltering height and exponential attenuation coefficient. As a result, the parameterisation is responsive to detailed ground roughness arrangements and flow conditions, including roughness height variations, element orientation, incident flow direction, transverse displacements, etc. Model-predicted effective roughness heights, wall stress, mean velocity at the height of the roughness, and in some cases displacement height, are compared against the LES measurements from this study as well as numerical/experiment measurements from other authors. The predictions from the model are found to agree well with the measurements both in trends and in absolute values, thus extending the applicability of the analytical rough wall model to more general surfaces than those previously tested.",
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    Large eddy simulations and parameterisation of roughness element orientation and flow direction effects in rough wall boundary layers. / Yang, Xiang; Meneveau, C.

    In: Journal of Turbulence, Vol. 17, No. 11, 01.11.2016, p. 1072-1085.

    Research output: Contribution to journalArticle

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    AU - Meneveau, C.

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    AB - We conduct a series of large eddy simulations (LES) of turbulent boundary layers over arrays of cuboidal roughness elements at arbitrary orientation angles (non-frontal orientations with the incident flow). Flow response to changing roughness orientation is systematically studied at two ground coverage densities, λp = 0.06 and 0.11. As expected, the effective roughness heights zo measured from LES are higher for λp = 0.11 than for λp = 0.06, although appreciable changes both in zo and wall shear stress (friction velocity) are observed at both ground coverage densities as the roughness orientation angle changes. This suggests the necessity of accounting for detailed rough wall topology (including more information than just λp, λf) when relating rough wall morphology to its aerodynamic properties. To this end, a recently developed analytical rough wall parameterisation is used to predict the aerodynamic properties of the simulated rough surfaces. In this rough wall model, wake interactions among roughness elements are explicitly modelled using the concept of sheltering height and exponential attenuation coefficient. As a result, the parameterisation is responsive to detailed ground roughness arrangements and flow conditions, including roughness height variations, element orientation, incident flow direction, transverse displacements, etc. Model-predicted effective roughness heights, wall stress, mean velocity at the height of the roughness, and in some cases displacement height, are compared against the LES measurements from this study as well as numerical/experiment measurements from other authors. The predictions from the model are found to agree well with the measurements both in trends and in absolute values, thus extending the applicability of the analytical rough wall model to more general surfaces than those previously tested.

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