# Experimental Assessment of RANS Models for Wind Load Estimation over Solar-Panel Arrays
## 4 Results
### Pressure Distribution  
Pressure distributions obtained from the different simulations and the experimental measurements are reported in Figure 5 in terms of the pressure coefficient \(\mathcal{C}_{p}\).  
The pressure distributions on the 1 st panel are shown in Figure 5a. All of the numerical results show the same pattern observed by the experimental measurements. Nevertheless, the RANS simulations tend to slightly overestimate the pressure difference between the front and the back side of the panel. This pressure difference is mostly due to a strong suction in the back side resulting from the acceleration of the flow below the 1 st panel, which RANS simulations tend to overestimate.  
For the 2 nd panel, reported in Figure 5b, the three pressure-tap measurements of the back side show a constant pressure distribution, which is correctly reproduced by the numerical simulations. On the front side, measurements show that the pressure on the panel are not constant: the bottom corner has a lower pressure than in the backside of the previous panel; the rest of the panel, instead, has a slight recover in pressure. This behaviour is not reproduced by any of the simulations, which predict a constant pressure distribution in the front face of the 2 nd panel. The measured pressure difference between the front and back sides at 0.25\(c\) is accurately reproduced by the \(k\)-\(e\), SST \(k\)-\(\omega\) and RSM models, while the transition SST model fails in recovering it. On the contrary, for the points at 0.5\(c\) and 0.75\(c\) the transition SST model is the one to recover more accurately the measured pressure difference, while the other models show larger discrepancies. Both experiments and simulations shows lower pressure coefficient at the front side than at the back, which confirms that suction is occurring at the front side of the panel.  
Figure 5c shows the results for the 3 rd panel. It can be observed that the \(C_{p}\) measurements match very well with the SST \(k\)-\(\omega\) model, while the pressure difference between the front and back sides is slightly underestimated in the \(k\)-\(e\) model. In any case, both the numerical simulations predict that the pressure is almost constant at each side of the panel; this behaviour is confirmed by the experimental measurements. The transition SST and RSM models, instead, shows a more diverse behavior, with the first predicting almost zero pressure difference and the latter predicting slightly higher pressure difference for \(x/c=0.5\).  
Results for the 4 th panel are shown in Figure 5d. In this case, transition SST model reproduces more accurately than the other models the difference in pressure coefficients between the front and back side of the panel. Also on this panel the \(k\)-\(e\) model slightly underestimates the pressure coefficient difference between the front and back sides of the panel. The SST \(k\)-\(\omega\) and RSM models, instead, underestimate the pressure difference. Despite the differences in accuracy, all the turbulence models predict a constant pressure distribution along both the front and back sides of the panel, which is confirmed by the experimental measurements.