Flow over closely packed cubical roughness

Xu, Haosen; Altland, Samuel; Yang, Xiang; Kunz, Robert F.

doi:10.1017/jfm.2021.456

Cited by 22 publications

(35 citation statements)

References 60 publications

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“…We see that the data do not support (1.3) or the presence of K-H rollers. We also examined the data reported in Coceal et al (2007), Kanda et al (2004), and Xu et al (2021), but could not find K-H rollers. Huq et al (2007) carried out extensive visualization attempts in experiments, and they could not find K-H rollers either.…”

Section: Discussionmentioning

confidence: 97%

“…2011; Lozano-Durán & Jiménez 2014; Xu et al. 2021). The grid resolution requirement for rough-wall boundary layers is similar.…”

Section: Direct Numerical Simulationmentioning

confidence: 99%

“…The no-slip top surfaces of these rectangular roughness elements give rise to a sharp velocity gradient at the top of the canopy, and viscous diffusion becomes the dominant term in the momentum equation especially when the roughness packing density is sufficiently high (Xu et al. 2021). For these rectangular roughness arrays, the origin of the exponential profile cannot be at the top of the canopy, and a displacement must be incorporated …”

Section: The Exponential Profilementioning

confidence: 99%

“…2018; Xu et al. 2021), and the nominal Reynolds number and the effective Reynolds number are two. The nominal Reynolds number reads where is the nominal friction velocity, and is the kinematic viscosity.…”

Section: Direct Numerical Simulationmentioning

confidence: 99%

“…We now compare our grid resolution with those in the literature. The typical grid resolution requirement for flat-plate boundary-layer flow is Δx + ≈ 12, Δy + ≈ 6, and Δz + max ≈ 8 (Kim, Moin & Moser 1987;Lee et al 2011;Lozano-Durán & Jiménez 2014;Xu et al 2021). The grid resolution requirement for rough-wall boundary layers is similar.…”

Section: Direct Numerical Simulationmentioning

confidence: 99%

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Evidence for Raupach et al.'s mixing-layer analogy in deep homogeneous urban-canopy flows

et al. 2022

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The mixing-layer analogy is due to Raupach, Finnigan & Brunet (Boundary-Layer Meteorol., vol. 25, 1996, pp. 351–382). In the analogy, the flow in the roughness sublayer of a homogeneous deep vegetation canopy boundary layer is analogous to a plane mixing layer rather than a surface layer. Evidence for the analogy includes the inflected velocity profile, which resembles the velocity profile in a plane mixing layer, and, most notably, the following estimate as a result of the Kelvin–Helmholtz instability: $\varLambda _x=8.1L_s$ , where $\varLambda _x$ is the spacing of the large-scale eddies, and $L_s$ is the shear length. The mixing-layer analogy has been very successful in vegetation canopy flow research, but has received only limited support in urban-canopy flow research. This work revisits Raupach et al.'s mixing-layer analogy, and we present the evidence for the mixing-layer analogy in urban-canopy flows: the exponential velocity profile in the canopy layer, i.e. $(U-U_c)/(U_h-U_c)=\exp (z/L_m)$ , and $L_m\sim [(U_h/U_c-1)(U_h/U_c+3)]^{-1}$ . Here, $z$ is the vertical coordinate, $L_m$ is the attenuation length and is a measure of the largest eddy in the canopy layer, $U_h$ is the wind speed at the canopy crest and $U_c$ is the velocity in the inactive layer. We conduct direct numerical simulations of various deep homogeneous urban-canopy flows and test the above two scalings. We also discuss why Raupach et al.'s analogy has not seen as many successes in urban-canopy flows as in vegetation canopy flows.

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Section: Discussionmentioning

confidence: 97%

“…2011; Lozano-Durán & Jiménez 2014; Xu et al. 2021). The grid resolution requirement for rough-wall boundary layers is similar.…”

Section: Direct Numerical Simulationmentioning

confidence: 99%

Section: The Exponential Profilementioning

confidence: 99%

Section: Direct Numerical Simulationmentioning

confidence: 99%

Section: Direct Numerical Simulationmentioning

confidence: 99%

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Evidence for Raupach et al.'s mixing-layer analogy in deep homogeneous urban-canopy flows

et al. 2022

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Bridging the Urban Canopy Sublayer to Aerodynamic Parameters of the Atmospheric Surface Layer

Katul

2022

Boundary-Layer Meteorol

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Effects of Wall Topology on Statistics of Cube-Roughened Wall Turbulence

Zhou

Chen

et al. 2022

Boundary-Layer Meteorol

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In this work, we carried out roughness-resolved direct numerical simulations of cube-roughened turbulent channel flows to investigate the effects of aligned and staggered arrangements, element spacings, and element orientations on the statistics of rough-wall turbulence. The results show that the equivalent sandgrain roughness, Reynolds stresses and dispersive stresses are all affected by element spacings and arrangements, but in different ways depending on the cube orientations. Placing the roughness elements in a staggered way in general increases the equivalent sandgrain roughness, unless when the element-element interaction is insignificant for the cube orientation with wakes of short length.As for the Reynolds normal stresses and the streamwise component of the dispersive stresses (both are normalized by the total friction velocity), placing the cube elements in a staggered way decreases their maximal values when compared with the aligned arrangements. As for the effects of element spacing on the equivalent sandgrain roughness and the maximums of the Reynolds normal stresses, similar trends are observed for different element orientations and arrangements when increasing the element spacing l/r (where r is the cube width) from 2.0 to 2.8. When further increasing the element spacing l/r from 2.8 to 3.5, however, different trends are observed for different element orientations. As for the dispersive stresses, greater maximal values of their streamwise components are observed for larger element spacing for all the considered cube-roughened surfaces. For the turbulence statistics in the wake

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Flow over closely packed cubical roughness

Abstract: Abstract

Cited by 22 publications

References 60 publications

Evidence for Raupach et al.'s mixing-layer analogy in deep homogeneous urban-canopy flows

Evidence for Raupach et al.'s mixing-layer analogy in deep homogeneous urban-canopy flows

Bridging the Urban Canopy Sublayer to Aerodynamic Parameters of the Atmospheric Surface Layer

Effects of Wall Topology on Statistics of Cube-Roughened Wall Turbulence

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