Modeling vehicle-induced turbulence in large-eddy simulations: Formulation of a simple method and validation against wind tunnel experiments in an idealized street canyon

The transport and dilution of pollutants at street level are dominated by the combined effects of the turbulent
background flow and turbulence induced by the motion of vehicular traffic. A thorough understanding of these
effects is crucial for the ability to predict the spatial distribution of pollutants correctly. In this study, a new,
simple method for modeling vehicle-induced turbulence (VIT) in large-eddy simulations (LESs) of urban street
canyon flows is described. The method is validated by comparing results to wind tunnel data of (1) flow
around a resting car-shaped body and (2) a street-canyon setup with driving vehicles represented by moving
obstacles. The LESs indicate that the main features of the wake flow, including velocity deficit and recirculation
length, of a resting car-shaped vehicle is reproduced with good agreement to the experimental data, and shows
convergence at a grid spacing of 𝛥 = 0.05 m. In the street-canyon configuration, the simulations capture
the primary vortex structure, roof-level separation and associated shear-layer structure, and the associated
pollutant dispersion patterns. Moving traffic leads to enhanced vertical exchange and a reduction of incanyon pollutant concentrations, which is consistently reproduced by the model. ... mehrA systematic overprediction
of streamwise velocity and pollutant removal is observed, suggesting sensitivity to the representation of rooflevel momentum exchange. The additional computational cost introduced by the method remains limited
(approximately 1%–8%). Overall, these results indicate that the new method provides a simple tool for
investigating the influence of moving traffic on urban flow and pollutant dispersion in LES models.