# Experimental Simulation of Thunderstorm Profiles in an Atmospheric Boundary Layer Wind Tunnel
## 3 Experimental Setup  
The tests were carried out at the Giovanni Solari Wind Tunnel (WT) facility at the University of Genoa, which is a closed-circuit traditional atmospheric boundary layer WT (Figure 2). Its cross-section is rectangular, 1.70 m (width) \(\times\) 1.35 m (height), and the working section is 8.80 m long. The controllable wind speed range is 0.2-32 m/s.  
Figure 2: The Giovanni Solari Wind Tunnel at the University of Genoa.  
Atmospheric turbulent boundary layers are generally set up using an arrangement of roughness elements, distributed over the floor of the wind tunnel, and two-dimensional elements (spires and a fence) located at the inlet of the test section (Figure 3a). In order to reproduce the nose-shaped profile of a thunderstorm, a partial grid (TS grid) has been specifically designed based on practical experience, using preliminary work [47] as a foundation for the design process. The basic idea is to lower the flow velocity at the upper part of the test chamber, aiming to replicate the characteristic nose-shaped mean wind profile. To achieve this, modules with variable opening sizes were designed, allowing for variations in the shape of the profile, the height of the nose and the level of turbulence intensity. The TS grid is composed by different rectangular modules spanning the full width of the wind tunnel and including square openings of different dimensions. Currently, the laboratory is equipped with six modules, two by two, with small, intermediate and large openings, corresponding to porosities of about 40%, 45% and 50%, respectively. The partial grid is installed 4 m downstream of the WT inlet section and covers approximately two thirds of the height of the WT test section, as shown in Figure 3b.  
A geometrical scale of 1:400 was considered, based on the idea of using this setup for testing a tall building in future works. During the experiments, a dynamic multi-hole pressure probe (i.e., TFI Cobra probe) was used for measuring the flow three-component velocity fluctuations with a sampling frequency of 2 kHz. The accuracy of measurements was generally within \(\pm\)0.5 m/s and \(\pm\)1\({}^{\circ}\) pitch and yaw angle, up to about 30% turbulence intensity. The Cobra probe range of measurement was from 2 to 100 m/s within a \(\pm\)45\({}^{\circ}\) cone of its \(x\)-axis. The three components of the wind speed time histories were acquired approximately 3 m downstream from the TS grid's position for a number of key locations along the height of the wind tunnel. From the measured time histories, mean wind speed and longitudinal turbulence intensity profiles were derived.  
The experimental tests aimed to simulate the nose-like feature of the mean velocity vertical profile at the radial location where the maximum wind speed occurs, neglecting the unsteady characteristics of thunderstorm-downbursts. The measured mean wind speed profiles were compared with the analytical model developed by [PERSON] and [PERSON], Equation (3), for different heights of the nose. Two configurations of the roughness elements were considered, while several arrangements of the TS grid modules were tested in order to evaluate their influence on the shape of the mean wind speed profiles.