Computational Fluid Dynamics simulations of thunderstorm downburst winds

Thunderstorms are mesoscale non-synoptic wind events with potentially devastating implications for the integrity of low and mid-rise structures. The outflows of a thunderstorm commonly referred to as downbursts are characterized by a vertical impingement of cold air from the cloud base to the surface of the Earth followed by a divergent radial outflow dominated by the primary ring vortex responsible for severe winds. This study aims at investigating the physical characteristics of downburst winds from the perspective of wind loading of structures. Two downburst scenarios were considered: (Case 1) an isolated downburst wind, and (Case 2) a downburst immersed in an approaching atmospheric boundary layer (ABL) wind. For that purpose, the experimental campaigns previously performed in WindEEE Dome were recreated by means of Computational Fluid Dynamics (CFD) simulations. Both Case 1 and Case 2 were successfully validated with high-quality experimental tests in terms of vertical profiles of radial velocity. Although all three used CFD approaches (URANS, SAS and LES) showed decent levels of accuracy, LES demonstrated its superiority over the former two in terms of obtaining physically most meaningful representation of complex downburst flow conditions.