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 in-canyon pollutant concentrations, which is consistently reproduced by the model. A systematic overprediction of streamwise velocity and pollutant removal is observed, suggesting sensitivity to the representation of roof-level 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.