International Journal of Urban Management and Energy Sustainability

International Journal of Urban Management and Energy Sustainability

Effects of Various Turbulence Models on The Accuracy and Efficiency of A Two-phase Method For Studying Pollutant Dispersion in Urban Street Canyons

Document Type : Case Study

Authors
Department of Mechanical Engineering, Ya.C., Islamic Azad University, Yazd, Iran
Abstract
Air pollution in dense urban areas threatens public health, and street canyons, where pollutants accumulate under weak ventilation, are a critical setting for exposure assessment. Computational fluid dynamics is widely used to predict pollutant dispersion there, but the turbulence model governs both the accuracy and the cost of the prediction, and comparisons of Reynolds-averaged Navier–Stokes, large eddy simulation and hybrid RANS/LES approaches within a two-phase framework remain scarce. This study aims to identify an appropriate turbulence model for simulating pollutant dispersion in a three-dimensional urban street canyon. The standard k–ε model, the Smagorinsky sub-grid-scale model and a hybrid model that applies k–ε near the walls and LES in the outer flow were implemented in an in-house finite-volume code. Air and carbon dioxide were treated as separate phases, the interface was captured with the volume-of-fluid method, and convective fluxes were discretised with the second-order Van Leer scheme under isothermal conditions at Re = 50,000. The models were validated against wind-tunnel data. LES and the hybrid model resolved two counter-rotating vortices in the upstream canyon and faster pollutant removal, whereas the k–ε model predicted a single vortex and pollutant accumulation near the walls and corners. The hybrid model required 5.14 times less computing time than LES but 4.35 times more than the k–ε model. The hybrid model therefore offers the best balance between accuracy and computational cost for two-phase pollutant dispersion in street canyons, while LES remains the reference when accuracy is paramount.

Graphical Abstract

Effects of Various Turbulence Models on The Accuracy and Efficiency of A Two-phase Method For Studying Pollutant Dispersion in Urban Street Canyons

Highlights

·         LES, hybrid RANS/LES and k–ε models are compared in a two-phase street-canyon model.

·         Air and CO2 are separate phases captured with VOF and a second-order Van Leer scheme.

·         LES and hybrid models resolve two counter-rotating vortices; k–ε predicts only one.

·         The k–ε model overpredicts pollutant accumulation near canyon walls and corners.

·         Hybrid model runs 5.14 times faster than LES with the best accuracy–cost balance.

Keywords

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Volume 7, Issue 2 - Serial Number 2
Spring 2026
Pages 369-383

  • Receive Date 11 April 2026
  • Revise Date 28 May 2026
  • Accept Date 18 October 2026