Physical Investigation of Downburst Winds and Applicability to Full Scale Events

Thunderstorm winds, i.e. downbursts, are cold descending currents originating from cumulonimbus clouds which, upon the impingement on the ground, spread radially with high intensities. The downdraft phase of the storm and the subsequent radial outflow that is formed can cause major issues for aviation and immense damages to ground-mounted structures. Thunderstorm winds present characteristics completely different from the stationary Gaussian synoptic winds, which largely affect the mid-latitude areas of the globe in the form of extra-tropical cyclones. Downbursts are very localized winds in both space and time. It follows that their statistical investigation, by means of classical full scale anemometric recordings, is often inadequate in the view of accurately reconstruct the transient nature of the phenomenon. Wind tunnel tests in ad-hoc laboratories can fill this gap. Furthermore, downbursts never occur as isolated system in nature; they occur, in fact, embedded into the background Atmospheric Boundary Layer (ABL) flow and are influenced by the thunderstorm cell translation. In nature, the decomposition of the recorded downburst signals into component signals associated with the aforementioned contributions is often challenging or unfeasible. This study presents the results of the largest experimental campaign performed so far on downburst winds, where the physical behavior of downburst-like flows, simulated by means of the impinging jet technique, was thoroughly investigated in the spatiotemporal domain. The experiments were conducted in the Wind Engineering, Energy and Environment (WinEEE) Dome at Western University which allows the simultaneous generation of downburst and background ABL winds along with the simulation of the parent thunderstorm translation. For the first time, a clear understanding of the overall downburst dynamics and of the interactions that take place during the occurrence of the phenomenon is presented. Later, this study investigates, as a structural application, the aerodynamic ...