ERIES-CLIMATHUNDERR: Buoyancy effects on large-scale experimental downburst winds

Downburst winds are typically simulated in laboratory settings using two well-established techniques: (i) the gravity current (GC) method, which exploits density differences between a downdraft-like fluid and the surrounding air to generate a buoyant jet, and (ii) the impinging jet (IJ) method, which mechanically produces a downdraft using wind tunnel fans. Although the GC approach more accurately replicates the thermodynamic conditions that initiate and sustain downburst events, the IJ method is more commonly used in wind engineering due to its ability to generate higher velocities and to better reconstruct the near-ground wind field—where buildings and human activities are concentrated. However, the absence of buoyancy effects in IJ simulations can result in significant deviations in both the dynamics and geometry of the evolving downburst and vortex structures.

The ERIES-CLIMATHUNDERR project, supported by the Engineering Research Infrastructures for European Synergies (ERIES) under the European Union’s Horizon Europe Framework Programme, aimed for the first time to recreate large-scale gravity current downbursts at the Jules Verne Climatic Wind Tunnel (CSTB, Nantes, France). By introducing temperature differentials between the jet and the surrounding environment, notable variations were observed in both the magnitude and shape of near-ground wind profiles.

These experimentally generated flow fields were further tested against a 1:2000 topographic model of the Polcevera Valley in Genoa, Italy. Located at the northern edge of the Mediterranean basin, Genoa is a hotspot for thunderstorm activity, a situation expected to intensify with ongoing climate change. The city’s unique orography—with valleys and mountains in close proximity to the coastline—creates highly favorable conditions for the formation and intensification of thunderstorms.

The CLIMATHUNDERR project specifically investigated downburst wind development in the Genoese valley under two scenarios: downdraft impact 600 meters (i) offshore and (ii) onshore relative to the Voltri-Pra terminal port, situated at the mouth of the Polcevera Valley.

Advanced measurement techniques were employed to capture the evolving flow fields, including Large-Scale Particle Image Velocimetry (LS-PIV) and high-response thermocouples.