# Experimental Simulation of Thunderstorm Profiles in an Atmospheric Boundary Layer Wind Tunnel
## 4 Results and Discussion
### Turbulence Intensity Properties  
Due to the lack of a defined target profile for the longitudinal turbulence intensity, only realistic variation with height was checked, opposite to the trend of the mean wind speed profile, as pointed out in Section 2.3. Figure 6 shows the longitudinal turbulence intensity profiles for the measured mean wind speed profiles reported in Section 4.1. The trend of turbulence intensity with the height is in accordance with full-scale [2] and scaled [8; 10] measurements. In addition, it can be noticed that different levels of turbulence intensity can be achieved by modifying the roughness elements and the arrangement of the TS grid modules. Figure 7 shows the setups corresponding to the profiles plot in Figures 5 and 6. Lower turbulence intensities were obtained for the configurations corresponding to the profiles P21, P47 and P39, varying in a range between 8% and 12%, while for the other configurations, higher values were obtained, mainly for P44. In the cases of the profiles with \(z_{m}=60\) m (Figure 6a), the differences between the two configurations are the roughness elements and the addition in the inlet section, for P48, of a classic wooden grid to generate turbulence, which covers the entire area of the WT section (Figure 7a bottom). Figure 6b shows greater differences between turbulence intensities for heights above 60 m, and this may be related to the fact that the TS module closest to the WT roof was removed for P51, leaving it as an empty space (Figure 7b bottom). In Figure 6c, the increase in turbulence intensity can be detected for all heights: in P44, the two TS modules closest to the WT roof were removed with respect to P39 (Figure 7c). Overall, the tests have shown that is possible to obtain a mean wind speed profile in agreement with the Wood and Kwok model and to achieve different ranges of turbulence intensities. Considering that the used passive device can not reproduce the non-stationary characteristics of thunderstorms, stationary turbulence characteristics are obtained, corresponding to the reduced turbulence fluctuation. The literature is consistent in affirming that the PSD of the reduced turbulent fluctuation of thunderstorms has similar properties to the classical PSD of synoptic events (e.g., [3; 42]). Figure 8 shows the PSD of the longitudinal turbulence component at the height of the nose for the configurations analyzed in this Section, compared with the Von Karman model (VK). Figure 6: Measured longitudinal turbulence intensity profiles: (**a**) \(z_{m}=60\) m; (**b**) \(z_{m}=80\) m; (**c**) \(z_{m}=100\) m.  
A good agreement between the PSD of the recorded turbulence and the Von Karman model was verified, confirming that also the harmonic content of the simulated turbulence is in line with literature models. As a final point, it should be noted that the TS grids are installed relatively close to the WT test section where measurements on models would be performed. This proximity could potentially make the profile unstable or, in other words, vary within the turntable, leading to potentially inaccurate measurements. Therefore, additional measurements of wind profiles were conducted in order to verify the uniformity and symmetry of the flow within the turntable. Time histories of wind velocity were measured at four locations over the turntable, as shown in Figure 8(a). As a test case, Figure 8(b) shows the comparison between the measured profiles (P21) for different positions of the probe. A very good agreement between the measured profiles for the different locations can be observed in Figure 8(b), confirming the stability of the mean wind speed and turbulence intensity profiles over the turntable. Uniformity of the profile was also checked and verified for the configurations corresponding to all the profiles analyzed in this Section.