A numerical analysis of pollutant dispersion in street canyon: influence of the turbulent Schmidt number

Abstract

<jats:p>Realizing the growing importance and availability of motor vehicles, we observe that the main source of pollution in the street canyons comes from the dispersion of automobile engine exhaust gas. It represents a substantial effect on the micro-climate conditions in urban areas. Seven idealized-2D building configurations are investigated by numerical simulations. The turbulent Schmidt number is introduced in the pollutant transport equation in order the take into account the proportion between the rate of momentum turbulent transport and the mass turbulent transport by diffusion. In the present paper, we attempt to approach the experimental test results by adjusting the values of turbulent Schmidt number to its corresponding application. It was with interest that we established this link for achieving our objectives, since the numerical results agree well with the experimental ones. The CFD code ANSYS CFX, the k, e and the RNGk-e models of turbulence have been adopted for the resolutions. From the simulation results, the turbulent Schmidt number is a range of 0.1 to 1.3 that has some effect on the prediction of pollutant dispersion in the street canyons. In the case of a flat roof canyon configuration (case: runa000), appropriate turbulent Schmidt number of 0.6 is estimated using the k-epsilon model and of 0.5 using the RNG k-e model.</jats:p>

Air Pollution Dispersion Modelling in Urban Environment Using CFD: A Systematic Review

“…The breakdown of the results is presented in Figures 9 and 10. A concerning trend is observed: almost half of the reviewed publications either do not comply with the BPGs for the domain dimensions in the flow direction (e.g., [52,[55][56][57][58][59][60], reaching zero distance offsets between the domain boundaries and the outer buildings in [61]), or do not report these important domain parameters (e.g., [16,[62][63][64]). Conversely, there are articles [48,50,[65][66][67][68] where the upstream distance that was used is much higher than the minimum recommendation of 5H, ranging between 14H in [48] and 38H in [68].…”

“…Out of the 74 reviewed articles, 53 investigated gaseous pollutants, such as carbon monoxide (CO), sulfur hexafluoride (SF 6 ), ethylene (C 2 H 4 ), nitrogen oxides (NO x ), ethane (C 2 H 6 ), etc. (e.g., [46,50,56,61,67,70,72,73,82,83]). A total of 13 papers modelled the pollutant as a particulate matter (PM), which included both PM10 and PM2.5 [48,74,77,[84][85][86][87][88][89][90][91][92][93].…”

“…The turbulent Schmidt number is a free parameter, which occurs in the pollutant transport equation and represents the ratio between the rate of turbulent transport of momentum and the turbulent transport of mass [61]. Its value depends on the flow fields and the geometry, and it plays an important role in the accurate prediction of pollutant dispersion [61]. All the investigated papers used a value between 0.2 and 1.3.…”

“…All the investigated papers used a value between 0.2 and 1.3. In addition, 3 articles [61,99,111] investigated the influence of the value of the turbulent Schmidt number on pollutant dispersion, and all of them concluded that the effects should be studied individually for each case in order to determine the most appropriate value. Ref.…”

Causes and side effects of changing water quality in Khassa-Chai river in Kirkuk, Iraq

“…Increased climate variability has made both rainfall and dryness patterns more inconsistent and unpredictable in many areas. The variations in temperature have increased since 1975 and affected the frequent recurrence of severe drought and floods (Pantula, 2016;Abed, Bouarbi, Hamidou & Bouzit, 2017;Qasim, 2017;Paredes, Castillo, Viteri, Fuentes & Bodero, 2019). Over the past dedicates, the Khassa-Chai river was experienced a serious drought.…”