Mean Flow Near Edges and Within Cavities Situated Inside Dense Canopies

Banerjee, Tirtha; Katul, Gabriel G.; Fontan, Stefano; Poggi, Davide; Kumar, Mukesh

doi:10.1007/s10546-013-9826-x

Cited by 28 publications

(33 citation statements)

References 44 publications

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“…For the patch cases, tower 1 and 2 show the attenuated profile inside the canopy and they reach their free surface layer log profile in the canopy space. For the mean 10 vertical velocity profile W , the profiles inside and outside the canopy show significant difference possibly due to edge effects (Banerjee et al, 2013). One interesting observation is increased W magnitude close to the canopy top for the HH case, patch 1 and the tower 5 for patch 2, which is close to the next canopy, which are relevant for signatures of KH motion.…”

Section: Synchronization Analysismentioning

confidence: 92%

“…The representation of the canopy in the LES follows the standard distributed drag parameterization (Shaw and Schumann, 1992;Watanabe, 2004;Patton et al, 2016) by adding an additional term in the mo-5 mentum budget equations as F di = C d a |u|u i where a is a one sided frontal plant area density (PAD), C d is a dimensionless drag coefficient assumed to be 0.3 (Katul et al, 2004;Banerjee et al, 2013), |u| is the resolved wind speed and u i is the resolved velocity component (i = 1, 2, 3, i.e. u, v and w), i.e.…”

Section: Large Eddy Simulations (Les)mentioning

confidence: 99%

“…In numerical modeling of canopy turbulence, the canopy is represented (as a sink for momentum) by a drag force F c = C d aU |U |, where C d is the drag coefficient typically between 0.1 0.3 (Banerjee et al, 2013), a is the vertical leaf area density profile, the integration of which over the canopy height yields the aforementioned PAI; U is the mean longitudinal velocity profile and |U | is the mean wind speed profile. Both Reynolds averaged Navier Stokes (RANS) modeling (Katul et al, 2004;Banerjee et al, 2013) and large eddy simulations (LES) of canopy turbulence (Shaw and Schumann, 1992) use this formulation.…”

mentioning

confidence: 99%

“…Both Reynolds averaged Navier Stokes (RANS) modeling (Katul et al, 2004;Banerjee et al, 2013) and large eddy simulations (LES) of canopy turbulence (Shaw and Schumann, 1992) use this formulation.…”

mentioning

confidence: 99%

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Revisiting Kelvin Helmholtz Instabilities and von Kármán Vortices in Canopy Turbulence

Banerjee

Roo

Linn

2017

Preprint

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Abstract. Studying turbulence in vegetation canopies is important in the context of a number of micrometeorological and hydrological applications. While recent focus has shifted more towards exploring different kinds of canopy heterogeneities, there are still gaps in the existing knowledge on the multiple types of dynamics involved in the case of horizontally homogeneous canopies. For example, experimental studies have indicated that turbulence in the canopy sublayer (CSL) can be divided into three regimes. In the deep-zone, the flow-field is dominated by von Kármán vortex streets and interrupted by strong sweep 5 events. The second zone near the canopy top is dominated by attached eddies and Kelvin-Helmholtz waves associated with the velocity inflection point in the mean longitudinal velocity profile. Above the canopy, the flow resembles classical boundary layer flow. In this study, these different kinds of dynamics are studied together by means of a large eddy simulation (LES).The main theme of this work is to address the question whether the parametrization of the canopy by a distributed drag force in numerical simulations instead of placing real solid obstacles is consistent with the three layer conceptual model. Unique 10 techniques such as measures from information theory and coupled oscillator analysis are used to extract the coherent structures associated with the two motions. It can be stated that a better understanding of the rich dynamics associated with the simplest case of canopy turbulence can lead to more efficient simulations and more importantly improve the interpretation of more complex scenarios.

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Section: Synchronization Analysismentioning

confidence: 92%

Section: Large Eddy Simulations (Les)mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Revisiting Kelvin Helmholtz Instabilities and von Kármán Vortices in Canopy Turbulence

Banerjee

Roo

Linn

2017

Preprint

Self Cite

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“…Strong difference of surface properties and large swaths of such surface patches are known to induce secondary circulations (Mah-10 fouf et al, 1987;Dalu and Pielke, 1993;Raupach and Finnigan, 1995;Courault et al, 2007;van Heerwaarden and Guerau de Arellano, 2008;Garcia-Carreras et al, 2010;Banerjee et al, 2013;Dixon et al, 2013;Sühring and Raasch, 2013;Kang and Lenschow, 2014;Van Heerwaarden et al, 2014). Recent works by Mauder et al (2007), Stoy et al (2013) and Eder et al (2014) have suggested that non-closure of energy balance is also related to advection and flux divergence due to secondary circulations (Kanda et al, 2004;Foken, 2008).…”

mentioning

confidence: 99%

Turbulent transport of energy across a forest and a semi-arid shrubland

Banerjee¹,

Brugger²,

Roo³

et al. 2017

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Abstract. The role of secondary circulations has recently been studied in the context of well defined surface heterogeneity in a semi-arid ecosystem where it was found that energy balance closure over a desert-forest system and the structure of the boundary layer was impacted by advection and flux divergence. As a part of the CliFF (Climate Feedbacks and benefits of semiarid forests, a collaboration between KIT, Germany and the Weizmann Institute, Israel) campaign, we studied the boundary layer dynamics and turbulent transport of energy corresponding to this effect in the Yatir forest situated in the Negev desert 5 in Israel. The forest surrounded by small shrubs presents a distinct feature of surface heterogeneity, allowing us to study the differences between their interactions with the atmosphere above by conducting measurements with two EC stations and two Doppler LiDARs. As expected, the turbulence intensity and vertical fluxes of momentum and sensible heat are found to be higher above the forest compared to the shrubland. Turbulent statistics indicative of nonlocal motions are also found to differ over the forest and shrubland and also display a strong diurnal cycle. The production of turbulent kinetic energy (TKE) over the 10 forest is strongly mechanical, while buoyancy effects generate most of the TKE over the shrubland. Overall TKE production is much higher above the forest compared to the shrubland. The forest is also found to be more efficient in dissipating TKE.The TKE budget appears to be balanced on average both for the forest and shrubland, although the imbalance of the TKE budget, which contains the role of TKE transport, is found to be quite different in terms of their variation with atmospheric stability and diurnal cycles for the forest and shrubland. The effect of very large mesoscale motions is also directly quantified 15 following a recent formulation by Banerjee and Katul, 2013, using the measured longitudinal velocity variances and boundary layer heights. The difference of turbulent quantities and the relationships between the components of TKE budget are used to infer the characteristics of turbulent transport of energy between the desert and the forest.

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Street canyon ventilation: Combined effect of cross‐section geometry and wall heating

Ridolfi

Salizzoni

2020

Quart J Royal Meteoro Soc

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Understanding the dynamics of mass exchange between a street canyon and the overlying atmosphere is crucial to predict air quality in urban areas. Despite the large number of studies on this topic, there are many aspects that still need to be clarified. Among these, one is certainly the role of thermal stratification in street canyon ventilation. In order to fill this gap, this study evaluates how the combined effect of street canyon geometry, wall roughness and differential heating of the building facades influences pollutant dispersion within the canyon and out of it. The study was carried out in a wind tunnel, adopting an idealized urban geometry made up of square bars placed normal to the wind direction. The boundary conditions inside the canyon were modified by heating its windward and leeward walls, by changing its aspect ratio and by introducing roughness elements at the walls. A passive scalar was injected from a line source at ground level. The flow and concentration fields were measured in a cross‐section of the canyon. Characteristic exchange velocities within the canyon and towards the external flow were estimated comparing the experimental data with an analytical model for the cavity wash‐out. Results show that the transition from one recirculating cell to two counter‐rotating cells inhibits canyon ventilation, with a consequent increase in pollutant concentration at the pedestrian level. This transition occurs as the cavity aspect ratio increases and is facilitated by adding roughness elements at the windward wall. Heating the leeward wall has negligible effects on canyon ventilation. Heating the windward wall accelerates pollutant removals in square cavities, while it contributes to a worsening of air quality in narrow cavities. Finally, the wash‐out times of the cavity are discussed in terms of a relative contribution of the mean advective motion and its turbulent counterpart.

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Mean Flow Near Edges and Within Cavities Situated Inside Dense Canopies

Cited by 28 publications

References 44 publications

Revisiting Kelvin Helmholtz Instabilities and von Kármán Vortices in Canopy Turbulence

Revisiting Kelvin Helmholtz Instabilities and von Kármán Vortices in Canopy Turbulence

Turbulent transport of energy across a forest and a semi-arid shrubland

Street canyon ventilation: Combined effect of cross‐section geometry and wall heating

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