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Louka, P.; Vachon, G.; Sini, J.-F.; Mestayer, P.G.; Rosant, J.-M.

doi:10.1023/a:1021355906101

Cited by 98 publications

(10 citation statements)

References 9 publications

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“…The major issue with the temperature-difference definition is the computation of the reference air temperature. Most studies [12][13][14]31,49] in Table 2 chose the air temperature measured above the canyon rooftop as the reference (at the same elevation used for measuring the free-stream velocity). The remaining studies [30,34,50] in Table 2 used the mean canyon temperature as the reference.…”

Section: Physical Parameters Set-up In View Of Field-experiments Evidencesmentioning

confidence: 99%

“…Thus, the definition of a local non-dimensional parameter seems more appropriate although rather complex. In this context, the use of building-building or surface-canyon air temperature differences seem suitable choices: the former addresses the local source of the buoyancy force but it can become of critical computation when the street is also heated; the latter directly infers the buoyancy effect of the canyon air temperature, a fair approximation if the canopy air temperature is isothermal away from the surfaces (e.g., Louka et al [31]). As for the reference velocity, a characteristic canyon velocity would address the typical flow intensity of the investigated in-canyon circulation.…”

Section: Additional Thoughts On the Use Of A Local Richardson Numbermentioning

confidence: 99%

“…A limited number of studies have used the convective-regime classification given by the Richardson number to investigate the buoyancy force and thermally-driven flows in urban canyons, with no definitive conclusions on their impact on the observed regimes. Given the flow inertia, the intensity and direction of the buoyancy force have determined an intensification/enlargement or weakening/shrink of the inertial vortex [28,29], or the formation of one/more counter-rotating vortex/vortexes both from field measurements [30] and numerical simulations [31]. However, in the same study by Louka et al [31], a single recirculation vortex has been observed from field data, with the heating effect of the build-ing facade being confined in a thin layer close to the same building.…”

Section: Introductionmentioning

confidence: 99%

“…Given the flow inertia, the intensity and direction of the buoyancy force have determined an intensification/enlargement or weakening/shrink of the inertial vortex [28,29], or the formation of one/more counter-rotating vortex/vortexes both from field measurements [30] and numerical simulations [31]. However, in the same study by Louka et al [31], a single recirculation vortex has been observed from field data, with the heating effect of the build-ing facade being confined in a thin layer close to the same building. This second outcome is in agreement with other studies (e.g., [14,[32][33][34]) which only observed an intensification of the upwards motion at the heated facade.…”

Section: Introductionmentioning

confidence: 99%

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Large-Eddy Simulation Analyses of Heated Urban Canyon Facades

2021

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Thermal convective flows are common phenomena in real urban canyons and strongly affect the mechanisms of pollutant removal from the canyon. The present contribution aims at investigating the complex interaction between inertial and thermal forces within the canyon, including the impacts on turbulent features and pollutant removal mechanisms. Large-eddy simulations reproduce infinitely long square canyons having isothermal and differently heated facades. A scalar source on the street mimics the pollutant released by traffic. The presence of heated facades triggers convective flows which generate an interaction region around the canyon-ambient interface, characterised by highly energetic turbulent fluxes and an increase of momentum and mass exchange. The presence of this region of high mixing facilitates the pollutant removal across the interface and decreases the urban canopy drag. The heating-up of upwind facade determines favourable convection that strengthens the primary internal vortex and decreases the pollutant concentration of the whole canyon by 49% compare to the isothermal case. The heating-up of the downwind facade produces adverse convection counteracting the wind-induced motion. Consequently, the primary vortex is less energetic and confined in the upper-canyon area, while a region of almost zero velocity and high pollution concentration (40% more than the isothermal case) appears at the pedestrian level. Finally, numerical analyses allow a definition of a local Richardson number based on in-canyon quantities only and a new formulation is proposed to characterise the thermo-dynamics regimes.

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Section: Physical Parameters Set-up In View Of Field-experiments Evidencesmentioning

confidence: 99%

Section: Additional Thoughts On the Use Of A Local Richardson Numbermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Large-Eddy Simulation Analyses of Heated Urban Canyon Facades

2021

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“…Vardoulakis S has attempted to figure out the pollutant concentration in urban areas during one day and one week [7]. MUST Experiment [8] and the Nantes' 99 Experiment [9] have also presented good patterns about pollution dispersion in a large scale. Both of them have provided a close agreement between simulation results and other validated models.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation of NOx and Particular Matter Distribution from Urban Street in Beijing China

Liu

Wang

2016

MATEC Web Conf.

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Abstract:In recent years, air quality has been a nation-wide issue in Beijing, China with frequent appearance of haze. Disappointingly, most detectors and sensors are mounted in suburb regions that are over ten kilometers away from the center of Beijing. Additionally, most researches are focusing on a general air flow in large scale instead of a specific community. It is important to be aware of the air quality at living communities in urban areas due to a large population. In this study, computational fluid dynamic (CFD) technologies were used to analyze the distribution of NOx and particular matter (PM) from urban street in Beijing to evaluate the air quality at a certain building. As most air pollutions are caused by vehicle emissions in urban areas, containing NOx and particular matters, traffic emissions were considered as the only source of contaminants in this study. Commercial software ANSYS Fluent ® was used to simulate a number of dispersion scenarios under different boundary conditions to quantify the pollution level for the selected living environment in Beijing, China. Mass fraction, isosurfaces and streamlines of contaminant were presented to analyze the pollution distribution around the area.

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Driving physical mechanisms of flow and dispersion in urban canopies

Klein

Leitl

Schatzmann

2007

Intl Journal of Climatology

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Abstract:The paper summarizes results from recent full-scale and wind-tunnel studies and discusses the complexity of urban canopy layer (UCL) flow and related challenges for urban modeling. Wind-tunnel data for idealized street-canyon intersections demonstrate that street-level flow and dispersion patterns are significantly altered for configurations with non-uniform building heights. For most wind directions, concentration maxima were upto a factor of 2 higher for cases with taller buildings near the intersection. Enhanced vertical downward mixing in the wakes of the taller buildings apparently causes higher street-level winds close by, but simultaneously, other regions become sheltered from active mixing and poor ventilation. The analysis of Joint Urban 2003 (JU2003) full-scale data also pointed out that high-momentum fluid can be effectively mixed down in the wakes of high-rise buildings, and that UCL flow is predominantly dynamically driven by roof-level winds. Building-height variability is thus, a key factor for UCL dynamics and mixing.Additionally, a linear model, which assumes that the along-and across-canyon velocity components are directly proportional to their above roof-level counterparts, has then been tested. The complexity of UCL flow patterns cannot be captured by such a simple model, but it may be useful for estimating street-level winds. For the along-canyon component, more than 70% of the calculated values were within a factor of 2 of the measured values, while for the across-canyon component less than 50% of the predictions agreed within a factor of 2. The practical applicability of the model was further assessed using JU2003 wind-tunnel data and a comparison between JU2003 wind-tunnel and full-scale flow profiles is also presented. It becomes obvious that UCL flow patterns are significantly altered by changes in upwind wind direction of less than 10°. While the field and laboratory results are qualitatively in good agreement, noticeable differences exist at certain sites.

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Untitled

Cited by 98 publications

References 9 publications

Large-Eddy Simulation Analyses of Heated Urban Canyon Facades

Large-Eddy Simulation Analyses of Heated Urban Canyon Facades

Numerical Simulation of NOx and Particular Matter Distribution from Urban Street in Beijing China

Driving physical mechanisms of flow and dispersion in urban canopies

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