Numerical Investigation of Flow and Dispersion over Two-Dimensional Semi-Open Street Canyon

Authors

  • Muhammad Fatih Ibrahim School of Mechanical Engineering, College of Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Malaysia
  • Mohd Faizal Mohamad School of Mechanical Engineering, College of Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Malaysia
  • Naoki Ikegaya Faculty of Engineering Sciences, Kyushu University, 6-1 Kasuga-koen, Kasuga-shi, Fukuoka 816-8580, Japan
  • Azli Abd Razak School of Mechanical Engineering, College of Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Malaysia

DOI:

https://doi.org/10.37934/cfdl.15.2.5370

Keywords:

Semi-open canyon, scalar dispersion, eave, CFD, RANS

Abstract

A semi-open street canyon is able to protect pedestrians from unpleasant situations such as direct sunlight and rain. However, the protruding elements of the two opposite building facades that form the semi-open configuration can affect the air quality of the urban canopy layer (UCL). Therefore, this paper investigated the influence of the eave structures on the flow and pollutant dispersion over an idealized 2D street canyon with a unity aspect ratio. The length of the eaves was varied into 0.25H and 0.5H (H is the building height) and placed either on the leeward wall, the windward wall, or on both building facades located at the same elevation as the street canyon. Numerical simulations were performed using the steady-state Reynolds-averaged Navier-Stokes (RANS) equations in conjunction with Re-Normalization Group (RNG) k-ε as the turbulence closure model. The pollutant was released from a line source in the center of the bottom of the target canyon with uniform flow rate. Six different eave configurations were simulated in the wind direction perpendicular to the canyon axis, representing the worst condition of canyon ventilation. The evolution of the primary vortex, which occupied the entire canyon with the characteristic of skimming flow, showed less dependence on the length and position of the eave, except for the longest eave on the windward wall. However, the position of the vortex center depicted opposite results. The pollutant concentration is always higher near the leeward wall, but for the eave that protrudes from the windward wall with a length of 0.5H, the pollutant accumulates near the windward region. The ratio of pollutant concentration showed higher concentration in the semi-open configurations compared to the fully open layout as a result of limited penetration of shear flow into the canyon, which leads to deterioration of pollutant removal.

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Author Biographies

Muhammad Fatih Ibrahim, School of Mechanical Engineering, College of Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Malaysia

muhammadfatihibrahim@gmail.com

Mohd Faizal Mohamad, School of Mechanical Engineering, College of Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Malaysia

faizal3744@uitm.edu.my

Naoki Ikegaya, Faculty of Engineering Sciences, Kyushu University, 6-1 Kasuga-koen, Kasuga-shi, Fukuoka 816-8580, Japan

ikegaya@cm.kyushu-u.ac.jp

Azli Abd Razak, School of Mechanical Engineering, College of Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Malaysia

azlirazak@uitm.edu.my

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Published

2023-01-20

How to Cite

Ibrahim, M. F., Mohamad, M. F., Ikegaya, N., & Abd Razak, A. (2023). Numerical Investigation of Flow and Dispersion over Two-Dimensional Semi-Open Street Canyon. CFD Letters, 15(2), 53–70. https://doi.org/10.37934/cfdl.15.2.5370

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