CFD simulation of thunderstorm outflow and atmospheric boundary layer winds interactions in urban canyons: Validation and flow dynamics

Thunderstorm outflows generate intense near-ground winds that pose significant risks to urban infrastructure. However, outflow wind actions are not included in structural design codes because their interactions with urban environments are not yet fully understood. This study employs Computational Fluid Dynamics (CFD) to simulate outflow propagation in urban canyons under the influence of background atmospheric boundary layer (ABL) winds. Wind tunnel measurements are used to validate the CFD results, with a focus on the performance of Reynolds-Averaged Navier–Stokes turbulence models. The low-Reynolds k − ε model, combined with a highly refined mesh ( y + <5), effectively captures near-wall flow dynamics and accurately replicates experimental data. CFD reveals critical flow details at the surface, where outflow peaks, and at rooftop levels—areas that are often inaccessible to physical instruments. Interestingly, peak velocities in weak ABL wind conditions are significantly higher than in stronger ABL wind cases, highlighting nonlinear interactions between ABL and outflow winds. Compared to open terrain (i.e., no canyon), low-rise (15 m) and high-rise (50 m) urban canyons increase peak near-ground wind velocities by over 70 % and 130 %, respectively, under a weak ABL wind condition. The canyon geometry confines the outflow by preventing its radial spread and, therefore, maintains high velocities over greater vertical and radial distances. By complementing experimental studies, CFD offers valuable insights into urban wind behavior and supports efforts to enhance wind resilience in cities. • CFD simulations of outflow-ABL wind interaction in urban canyons validated with wind tunnel data. • Five RANS turbulence models evaluated for accuracy. • Low- Re model with highly refined mesh ( y + <5) best matches experiments. • Complex interaction between outflow and ABL winds prevents simple addition. • Urban canyons amplify peak velocity by over 130 % with respect to open terrain and retain high winds longer.