A numerical investigation on the interaction of a thunderstorm downburst and an atmospheric boundary layer wind

Downburst winds rarely occur as an isolated phenomenon. Instead, they are more likely to occur in the presence of background Atmospheric Boundary Layer (ABL) winds. However, only a limited number of studies have investigated this interaction. This study provides new insights into the interaction between ABL flow and downburst winds by analyzing velocity profiles, peak values, and spatiotemporal characteristics using Computational Fluid Dynamics (CFD) simulations. ABL and downburst winds previously reproduced in the WindEEE Dome facility are here numerically simulated with three approaches: URANS, SAS and LES. The interaction at the colliding front generates a stagnation region that slows down the Primary Vortex (PV) propagation, while significant levels of ABL entrainment into the downburst are observed. The PV at the along ABL direction is found to cause the strongest radial outflows. At these locations, a short-lived counter-rotating Secondary Vortex (SV) also develops. Although structural models are not included in the simulations, the study emphasizes the importance of accurately resolving the wind field that affects the wind loading on structures during such events. In addition to the limited amount of high-resolution full-scale data available, the present analysis contributes to advancing the knowledge of the complex dynamics of ABL-downburst interaction. The flow fields presented here are valuable as loading input conditions in structural analyses, and particularly useful for assessing fluid-structure interaction response of slender infrastructure like transmission line towers and telecommunication towers.