Turbulence Structure Within and Above a Canopy of Bluff Elements

Böhm, Margi; Finnigan, John; Raupach, Michael; Hughes, Dale

doi:10.1007/s10546-012-9770-1

Cited by 63 publications

(51 citation statements)

References 38 publications

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“…13. Previous studies of boundary-layer flow over an uniform strip canopy and of boundary-layer flow over a tree-like canopy also reported a P s peak in correspondence with z γ (see Raupach et al (1991) and Böhm et al (2013)). P s decreases rapidly from its peak location to approximately zero at the wall, indicating a relatively calm zone in the lower UCL.…”

Section: Turbulent and Wake Kinetic Energymentioning

confidence: 74%

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Spatial Characteristics of Roughness Sublayer Mean Flow and Turbulence Over a Realistic Urban Surface

Giometto

Christen

Meneveau

et al. 2016

Boundary-Layer Meteorol

141

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Single-point measurements from towers in cities cannot properly quantify the impact of all terms in the turbulent kinetic energy (TKE) budget and are often not representative of horizontally-averaged quantities over the entire urban domain. A series of large-eddy simulations (LES) is here performed to quantify the relevance of non-measurable terms, and to explore the spatial variability of the flow field over and within an urban geometry in the city of Basel, Switzerland. The domain has been chosen to be centered around a tower where single-point turbulence measurements at six heights are available. Buildings are represented through a discrete-forcing immersed boundary method and are based on detailed real geometries from a surveying dataset. The local model results at the tower location compare well against measurements under near-neutral stability conditions and for the two prevailing wind directions chosen for the analysis. This confirms that LES in conjunction with the immersed boundary condition is a valuable model to study turbulence and dispersion within a real urban roughness sublayer (RSL). The simulations confirm that mean velocity profiles in the RSL are characterized by an inflection point z γ located above the average building height z h . TKE in the RSL is primarily produced above z γ , and turbulence is transported down into the urban canopy layer. Pressure transport is found to be significant in the very-near-wall regions. Further, spatial variations of time-averaged variables and non-measurable dispersive terms are important in the RSL above a real urban surface and should therefore be considered in future urban canopy parametrization developments.

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Section: Turbulent and Wake Kinetic Energymentioning

confidence: 74%

“…2). The lower part of the RSL (z/z h < 2) is mainly composed of wake and of non-wake regions (Böhm et al 2013), whereas higher up in the boundary layer the flow organizes itself into a set of relatively high-speed and low-speed streamwise elongated streaks.…”

Section: Properties Of the Instantaneous Velocity Fieldmentioning

confidence: 99%

Spatial Characteristics of Roughness Sublayer Mean Flow and Turbulence Over a Realistic Urban Surface

Giometto

Christen

Meneveau

et al. 2016

Boundary-Layer Meteorol

141

View full text Add to dashboard Cite

show abstract

“…These include blocks of foam rubber (Rodrigo et al, 2007), Lego™ bricks, Meccano™ wheels (Stacey et al, 1994), wooden pegs, wire mesh (Aubrun and Leitl, 2004), miniature fir trees (Lee and Lee, 2012), bottle brushes (Liang et al, 2005), 3D printed fractal models (Bai et al, 2012), automotive bulbs (Bohm et al, 2013) and architectural model trees (Meroney, 1968;Endalew et al, 2009b;Ruck et al, 2012). Each of these materials have their own merits and allow various aspects of canopy flows to be investigated faster, cheaper and in greater detail than a full-scale experimental campaign.…”

Section: Model Treesmentioning

confidence: 99%

“…Similarly, the ridged branches are unable to streamline to the incident flow which results in a coefficient of drag which is independent of the magnitude of the incident wind speed which is not the case in actual canopies (Molina-Aiz et al 2006). Also, as discussed in Bohm et al (2013), the use of scale models of vegetation in wind tunnels may result in the flow being dominated by viscous drag which will not be representative of full-scale flows. However, the use of non-bluff bodies to represent forest canopies in wind tunnels is not without precedent (Meroney, 1968;Liang et al, 2005;Endalew et al, 2009b;Lee and Lee, 2012;Ruck et al, 2012).…”

Section: Model Treesmentioning

confidence: 99%

“…The dimensionless Reynolds number, Re, which relates the relative importance of viscous and inertial forces, is an important consideration when assessing the relevance of wind tunnel experiments, particularly given the concerns raised in Bohm et al (2013) relating to the use of non-bluff bodies to represent forest canopies at wind tunnel scale. This quantity is defined as:…”

Section: Reynolds Number Dependencementioning

confidence: 99%

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A study on the inclusion of forest canopy morphology data in numerical simulations for the purpose of wind resource assessment

Desmond

Watson

Aubrun

et al. 2014

Journal of Wind Engineering and Industrial Aerodynamics

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A series of numerical simulations of the flow over a forest stand have been conducted using two different turbulence closure models along with various levels of canopy morphology data. Simulations have been validated against Stereoscopic Particle Image Velocimetry measurements from a wind tunnel study using one hundred architectural model trees, the porosities of which have been assessed using a photographic technique.It has been found that an accurate assessment of the porosity of the canopy, and specifically the variability with height, improves simulation quality regardless of the turbulence closure model used or the level of canopy geometry included. The observed flow field and recovery of the wake is in line with characteristic canopy flows published in the literature and it was found that the shear stress transport turbulence model was best able to capture this detail numerically.

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First‐order turbulence closure for modelling complex canopy flows

Finnigan

Harman

Ross

et al. 2015

Quart J Royal Meteoro Soc

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Simple first‐order closure remains an attractive way of formulating equations for complex canopy flows when the aim is to find analytic or simple numerical solutions to illustrate fundamental physical processes. Nevertheless, the limitations of such closures must be understood if the resulting models are to illuminate rather than mislead. We propose five conditions that first‐order closures must satisfy, then test two widely used closures against them. The first is the eddy diffusivity based on a mixing length. We discuss the origins of this approach, its use in simple canopy flows and extensions to more complex flows. We find that it satisfies most of the conditions and, because the reasons for its failures are well understood, it is a reliable methodology. The second is the velocity‐squared closure that relates shear stress to the square of mean velocity. Again we discuss the origins of this closure and show that it is based on incorrect physical principles and fails to satisfy any of the five conditions in complex canopy flows; consequently its use can lead to actively misleading conclusions.

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Turbulence Structure Within and Above a Canopy of Bluff Elements

Cited by 63 publications

References 38 publications

Spatial Characteristics of Roughness Sublayer Mean Flow and Turbulence Over a Realistic Urban Surface

Spatial Characteristics of Roughness Sublayer Mean Flow and Turbulence Over a Realistic Urban Surface

A study on the inclusion of forest canopy morphology data in numerical simulations for the purpose of wind resource assessment

First‐order turbulence closure for modelling complex canopy flows

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