Intercomparison of Numerical Urban Dispersion Models — Part I: Street Canyon and Single Building Configurations

Sahm, Peter R.; Louka, P.; Ketzel, Matthias; Guilloteau, E.; Sini, J.-F.

doi:10.1007/978-94-010-0312-4_42

Cited by 13 publications

(27 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…4 and 5 are similar to those reported by e.g. Sahm et al (2002) and Hamlyn and Britter (2005), which confirm the reliability of our simulations. It is also worth noting that the value of β = k v 2 ref on the street canyon is equal to 0.02, corresponding to low turbulence conditions in the atmosphere.…”

Section: Resultssupporting

confidence: 92%

Mass Transfer Velocity and Momentum Vertical Exchange in Simulated Deep Street Canyons

Murena

Benedetto

D’Onofrio

et al. 2011

Boundary-Layer Meteorol

View full text Add to dashboard Cite

A box model to simulate mass transfer inside deep street canyons and with atmospheric flow above is introduced and discussed. Two ideal deep street canyons with aspect ratios of 3 and 5 (the aspect ratio being the ratio between building height and street width H/W ) are considered. This range of aspect ratios, found in many densely populated historical centres in Mediterranean cities as well as in other cities around the world, potentially creates high air pollutant concentration levels. Our model is based on a combination of analytical solutions and computation fluid dynamics (CFD) simulations using carbon monoxide (CO) as a tracer pollutant. The analytical part of the model is based on mass transfer velocity concepts while CFD simulations are used both for a preliminary validation of the physical hypothesis underlying the model (steady-state simulations) and to evaluate the concentration pattern with time (transient or wash-out simulations). Wash-out simulation curves were fitted by model curves, and mass transfer velocities were evaluated through a best-fitting procedure. Upon introducing into the model the contribution of traffic-produced turbulence, the modelled CO concentration levels became comparable with those obtained in real-world monitoring campaigns. The mass transfer rate between the canyon and the above atmosphere was then expressed in terms of an overall mass transfer velocity, which directly allows the evaluation of the mass transfer rate between the bottom volume of the canyon (pedestrian level) with the above atmosphere. Overall mass transfer velocities are reported as a function of the operating conditions studied (H/W = 3-5 and wind speeds = 2-8 m s −1 ). Finally, a simple expression is reported for determining pollutant concentrations at the pedestrian level based on the overall mass transfer velocity defined.

show abstract

Section: Resultssupporting

confidence: 92%

Mass Transfer Velocity and Momentum Vertical Exchange in Simulated Deep Street Canyons

Murena

Benedetto

D’Onofrio

et al. 2011

Boundary-Layer Meteorol

View full text Add to dashboard Cite

show abstract

“…Figure 6 shows the comparison between the experiments (symbols) and the CHENSI predictions (lines) of the U component mean velocity on five vertical profiles within the W/H = 1 cavity. A similar plot for the W/H = 2 case may be found in the paper of Sahm et al (2002). The data sets collapse extremely well within the shear layer above the canyon, with the most upstream profile (X/W = 0.09) well predicted immediately below the shear layer.…”

Section: Mean Profilessupporting

confidence: 79%

“…The data sets collapse extremely well within the shear layer above the canyon, with the most upstream profile (X/W = 0.09) well predicted immediately below the shear layer. Through the cavity the agreement is good, although CHENSI tends to underpredict the magnitude of the positive and reversed flow velocities, as noted by Sahm et al (2002). The discrepancy is greatest near the cavity base, probably due to the wall function used in the model.…”

Section: Mean Profilesmentioning

confidence: 80%

“…The von Neumann zero normal derivative condition is used at the top and outflow free boundaries, whilst the near wall region is described by the wall function of Launder and Spalding (1974). The initial experimental conditions, together with the W/H = 2.0 data set, have recently been a test case for numerical model intercomparison within several European institutions (Sahm et al, 2002). This showed that CHENSI predicted the mean flow field to an accuracy as good as the other models.…”

Section: Details Of the Numerical Simulationsmentioning

confidence: 99%

See 1 more Smart Citation

Influence of Geometry on the Mean Flow within Urban Street Canyons — A Comparison of Wind Tunnel Experiments and Numerical Simulations

Kovar-Panskus¹,

Louka²,

Sini³

et al. 2002

Urban Air Quality — Recent Advances

Self Cite

View full text Add to dashboard Cite

Abstract.A comparison between numerical simulations and wind tunnel modelling has been performed to examine the variation with streamwise aspect ratio (width/height, W/H) of the mean flow patterns in a street canyon. For this purpose a two-dimensional (2-D) cavity was subjected to a thick turbulent boundary layer flow perpendicular to its principal axis. Five different test cases, W/H = 0.3, 0.5, 0.7, 1.0 and 2.0, have been studied experimentally with flow measurements taken using pulsedwire anemometry. The results show that the skimming flow regime, with a large vortex in the canyon, occurred for all the cases investigated. For the cavities with W/H≤0.7 a weaker secondary circulation developed beneath the main vortex. The narrower the canyon, the smaller the wind speed close to the cavity ground, giving increasingly poor ventilation qualities. The corresponding numerical results were obtained with the Computational Fluid Dynamics (CFD) code CHENSI that uses the standard k-ε model. The intercomparison showed good agreement in terms of the gross features of the mean flow for all the geometries examined, although some detailed differences were observed.

show abstract

“…The lid-backward-facing step is recognized by many authors as the standard test to validate the turbulence models for these applications (i.e., Sahm et al, 2002;Vardoulakis et al, 2003;Chu et al, 2005). Additionally, it was demonstrated that k-ɛ turbulence model is usually the choice (e.g.…”

Section: Model Validationmentioning

confidence: 99%

CFD Simulation of the Dispersion of Exhaust Gases in a Traffic Loaded Street of Astana, Kazakhstan

Akhatova

Kassymov

Kazmaganbetova

et al. 2016

J. Urb. and Environ. Engng

View full text Add to dashboard Cite

Abstract:The aim of this paper is to consider one of the most traffic-loaded regions of Astana city (Kazakhstan) and to determine the concentration of carbon-monoxide (CO) in the air during the peak hours. CFD analysis based on the SolidWorks-EFD platform was used to simulate the dispersion of contaminants given the estimated emission rates and weather conditions at the crossroad of Bogenbay Batyr and Zhenis Avenues in Astana.Turbulence prediction was based on k-ε model with wall functions. The governing equations were discretized using the finite volume method and a 2 nd order spatial scheme. The mesh verification was based on 1% convergence criterion for a 50% of mesh density increment; air pressure near the wall of a selected building was chosen as the parameter to control the convergence. Numerical results are presented for prevailing conditions during all 4 seasons of the year, demonstrating that the highest levels of CO are recorded in summer and reach the values up to 11.2 ppm which are still lower than the maximum level admitted for humans. Nevertheless, obtained results show that Astana is gradually becoming a city that is likely to reach the critical levels of pollutants in the nearest future if control measures are not taken with enough anticipation. As for a future work, it is proposed to perform in-situ validation of specific scenarios to check and support the results obtained with CFD and to develop then specific policies for tackling the problem before it becomes evident.

show abstract

Intercomparison of Numerical Urban Dispersion Models — Part I: Street Canyon and Single Building Configurations

Cited by 13 publications

References 4 publications

Mass Transfer Velocity and Momentum Vertical Exchange in Simulated Deep Street Canyons

Mass Transfer Velocity and Momentum Vertical Exchange in Simulated Deep Street Canyons

Influence of Geometry on the Mean Flow within Urban Street Canyons — A Comparison of Wind Tunnel Experiments and Numerical Simulations

CFD Simulation of the Dispersion of Exhaust Gases in a Traffic Loaded Street of Astana, Kazakhstan

Contact Info

Product

Resources

About