https://hal-ineris.archives-ouvertes.fr/ineris-00961872/document

Modelling air quality in street canyons : a review

Recent progress in CFD modelling of wind field and pollutant transport in street canyons

Urban air quality is generally poor at traffic intersections due to variations in vehicles’ speeds as they approach and leave This paper examines the effect of traffic, vehicle and road characteristics on vehicular emissions with a view to understand a link between emissions and the most likely influencing and measurable characteristics It demonstrates the relationships of traffic, vehicle and intersection characteristics with vehicular exhaust emissions and reviews the traffic flow and emission models Most studies have found that vehicular exhaust emissions near traffic intersections are largely dependent on fleet speed, deceleration speed, queuing time in idle mode with a red signal time, acceleration speed, queue length, traffic-flow rate and ambient conditions The vehicular composition also affects emissions These parameters can be quantified and incorporated into the emission models There is no validated methodology to quantify some non-measurable parameters such as driving behaviour, pedestrian activity, and road conditions

Evaluating effects of traffic and vehicle characteristics on vehicular emissions near traffic intersections

Air flow inside an array of cubes is simulated. Cubes (edge length 0.15 m) are arranged in a regular array, separated by 0.15 m in the streamwise and spanwise directions. Numerical simulations are performed based on Reynolds-averaged Navier–Stokes equations (RANS), solved in a computational fluid dynamics model (CFD), with standard k–e turbulent closure (two prognostic equations are solved for the turbulent kinetic energy k and its dissipation e, respectively). Simulations are validated against wind-tunnel data using a technique based on hit-rate calculations, and calculated statistical parameters. The results show that the horizontal velocity is very well modelled, and despite some discrepancies, the model that fulfils the hit-rate test criteria gives useful results that are used to investigate three-dimensional (3-D) flow structures. The 3-D analysis of the flow shows interesting patterns: the centre of the canyon vortex is at 3/4 of the canyon height, and stronger downward than upward motions are present within the canyon. Such behaviour is explained by the presence of a compensation flow through the side of the canyon, which enters the canyon from the upper part and exits from the lower part. This complex 3-D structure affects the tracer dispersion, and is responsible for pollutant transport and diffusion.

CFD simulation of airflow over a regular array of cubes. Part I: Three-dimensional simulation of the flow and validation with wind-tunnel measurements

https://repository.ust.hk/ir/bitstream/1783.1-6640/1/main_content_200903201.pdf

Ana Pilar Garcia Sagrado

Papers

Numerical and experimental modelling of pollutant dispersion in a street canyon