LES simulations of downburst-ABL wind interactions and their impact on building aerodynamic loads

Downbursts generate localized and non-stationary outflows that differ fundamentally from the quasi-stationary atmospheric boundary layer (ABL) winds used in design standards. However, the combined effects of downburst outflows and background ABL winds on building aerodynamics and loads remain insufficiently characterized. This study employs large-eddy simulation (LES) to investigate the interaction between a downburst-like impinging jet (DB), an ABL wind, and a mid-rise benchmark building. A two-stage validation of the ABL wind-building and isolated DB cases confirmed adequate resolution of turbulent kinetic energy and correct inertial subrange behavior, with good agreement against wind-tunnel data. Combined ABL-DB simulations revealed two dominant flow features: a near-surface accelerating wall jet and an overlying velocity-deficit layer. Above the wall jet, the strong downdraft blocks the background ABL flow from penetrating the high-momentum jet core, producing a marked velocity deficit aloft. The ABL wind breaks the symmetry of the outflow, deflecting the wall jet downstream, shifting stagnation, intensifying near-ground velocities, and elongating the wake. At lower elevations, the peak ABL-DB velocity is approximately 33% higher than the mean ABL-DB value (plateau), highlighting the severe impact of downburst pulse on near-ground wind loading and wind–structure interactions. The building further modifies this compound flow through aerodynamic effects such as edge separation, roof-corner vortices, and downstream recirculation. An energy-based metric, the available dynamic pressure ratio (ADPR), showed strong near-ground energy concentration, with values substantially higher than ABL wind baseline. Surface pressure and integrated force analyses demonstrated that peak lateral loads under ABL-DB wind can exceed windward streamwise loads by up to 1.5 times. The results show that transient ABL-DB interactions fundamentally alter the building loading hierarchy, with lateral facades often governing, and must be explicitly considered in performance-based wind design.