A comprehensive comparison of RANS and LES simulations for pedestrian wind comfort assessment

Urban planning authorities often require pedestrian-level wind (PLW) assessments using computational fluid dynamics (CFD) for permitting. While PLW is typically conducted with Reynolds-averaged Navier–Stokes (RANS) simulations, there is ongoing debate among practitioners about using costlier Large Eddy Simulations (LES). This can be further complicated by an inconsistent definition of mean wind speed. This study compares RANS and LES across three benchmark cases: an isolated 1:1:2 block (A), the Michelstadt array (B), and the Niigata district (C). The results were validated against wind tunnel data using two wind speed metrics: magnitude of time-averaged velocity ( s m v ) and time-average of instantaneous speed ( s m s ). Results showed that LES performed better in predicting wind speeds, with higher Pearson correlations: Case A had LES at 0.97 and RANS at 0.86, while Case B showed LES at 0.93 and RANS at 0.72. For Case C, LES with s m s achieved the highest correlation (over 0.82) and the lowest average relative deviation across eight wind directions. However, LES- s m v underpredicted low-wind-speed areas similarly to RANS. Thus, RANS and LES validation discrepancies can arise from wind speed definitions. In terms of flow physics, RANS produces less mixing in wakes and prolonged wind deficits, resulting in milder Lawson comfort map activity classes.