# Experimental Assessment of RANS Models for Wind Load Estimation over Solar-Panel Arrays
## 4 Results  
### Mean Velocity Field  
Figure 4 reports contour plots of both experimental and numerical results for the average streamwise \(U\) (left column) and vertical \(V\) (right column) velocity components. All velocities are scaled with \(U_{\infty}\). When the flow encounters the 1 st panel, most of it is deflected upwards because of the panel inclination. The experimental results show that the mean vertical velocity increases over the 1 st panel, reaching \(U_{\infty}\) exactly when leaving at the top corner of the panel. This behaviour is correctly reproduced by the four numerical simulations. With respect to the flow passing under the panel, the information that can be extracted from the experiment is limited due to the presence of the panel shadow. Nevertheless, it is possible to observe that the mean vertical velocity decreases up to almost -\(U_{\infty}\) at the bottom corner. This effect as well is correctly reproduced by all the numerical simulations. Apart from the flow deflection over the 1 st panel, both experiments and RANS simulations show that the mean streamwise velocity of the flow is accelerated up to 1.5 \(U_{\infty}\) when leaving the top corner of the 1 st panel due to the blockage produced by the panel. However, experiment and simulations are found to differ on the size and the width of the region interested by the increase in velocity. The streamwise acceleration region past the top corner of the 1 st panel is slightly greater in magnitude according to \(k\)-\(\epsilon\), SST \(k\)-\(\omega\), and transition SST models (reaching a peak value of about \(\frac{U}{U_{\infty}}\approx 1.75\)) than in the experimental result (\(\frac{U}{U_{\infty}}\approx 1.5\)). Also the region is longer as the \(\frac{U}{U_{\infty}}=1.5\) contour line reaches the 4 th plate while in the experiment it seems to extend only up to the 2 nd plate. For the RSM model this region is considerably shorter and closer in value, thus being much more similar to that observed in the experimental results. According to PIV measurements the mean streamwise velocity of the flow passing under the panels is increased up to 1.5 \(U_{\infty}\) when leaving the 1 st panel, and starts decreasing below the 2 nd panel (\(x/c\approx 2\)), leaving the 4 th panel at a peak velocity approximately equal to \(U_{\infty}\). The numerical simulations agree with the experiment in that the mean streamwise velocity is increased up to 1.5 \(U_{\infty}\) when leaving the bottom corner of the 1 st panel, but they do not show the same progressive decrease in the following panels. Even though the maximum streamwise velocity when passing below the 2 nd panel reduces up to 1.3 \(U_{\infty}\), no further reduction occurs below the following panels, thus the flow leaves the 4 th panel at the same peak streamwise velocity. In the case of the transition SST model, it can be observed than the flow passing under the 4 th panel is locally accelerated in the streamwise direction up to 1.5 \(U_{\infty}\). Figure 4: Contour map of the average horizontal (**left column**) and vertical (**right column**) velocity components. From top to bottom, rows refer to experimental measurements, transitional SST, \(k\)-\(\omega\) SST, \(k\)-\(e\) and RSM. The horizontal and vertical dimensions are normalised with respect to the panel chord length \(c\). The velocity magnitude is normalised with respect to the inlet free-stream velocity measured in the wind tunnel. Solar panels are shown in black color. For experimental measurements, areas below the solar panels in which the laser illumination was not sufficient are blanked in white color. While moving past the 1 st panel, the flow separates at the bottom and top corners of the panel. A recirculation region forms behind the 1 st panel, in which flow is reversed in terms of the mean streamwise velocity, reaching \(-0.5~{}U_{\infty}\) in the experiment. This flow behaviour is reproduced by all the numerical simulations.