Performance of RANS, URANS and LES in the Prediction of Airflow and Pollutant Dispersion

The performance of 3 different CFD numerical approaches, namely RANS, URANS and LES are evaluated to determine their suitability in the prediction of airflow and pollutant dispersion in urban street canyons. Numerical results are evaluated against wind tunnel experimental data available from an online database (www.codasc.de). LES was observed to produce more accurate and reliable results compared to both RANS approaches, because LES resolves the inherent fluctuations, thus capturing the turbulent mixing process in the flow field within the canyon. Although URANS also computes for transience, it fails to account for unsteadiness, and hence is not an appropriate replacement for LES.

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