# Experimental Assessment of RANS Models for Wind Load Estimation over Solar-Panel Arrays
## 5 Conclusions  
The results of the RANS simulations with different solver models have been compared with experimental results for complex separated flows. These numerical methods are \(k\)-\(e\), SST \(k\)-\(\omega\), transitional SST and RSM. The experimental velocity and turbulent kinetic energy fields are investigated using PIV. Static pressure measurements are obtained by using pressure taps located on the surface model and a pressure transducer. The average velocity fields obtained from the different numerical methods are in good agreement when compared with the experimental ones. However, there are some flow features that are not reproduced by all models, like the stretching in the turbulent wake between the 3 rd and 4 th panel. A good prediction of the velocity fields and the thickness of the turbulent wake is very important to rely on the loads produced by the numerical methods. With respect to the pressure coefficients, the numerical models show different degrees of fidelity depending on the panel. All the numerical methods are reasonably good when simulating the pressure applied on the 1 st panel due to the free flow impact, but they tend to overestimate the difference between the front and back sides. \(k\)-\(e\) model tends to underestimate the pressure difference between the front and back sides. For the 3 rd and 4 th panel, \(k\)-\(e\) tends to underestimate the pressure coefficient difference between the front and back sides, while SST \(k\)-\(\omega\) provides a better estimation in the 3 rd panel and transition SST in the 4 th panel. In any case, all the numerical methods predicts correctly that the pressure is constant along the front and back sides when the flow is detached. In terms of the pressure coefficient difference between the front and back side of the panel, it seems that the methods that predicts better the thickness of the turbulent wake provides better results. \(k\)-\(e\) and SST \(k\)-\(\omega\) shows better behaviour that transition SST in this aspect. The predicted \(k\) by the different numerical models is more similar to the experimental Reynolds stress \(\overline{u^{\prime 2}}\) than to the \(k\). Most of the numerical methods analysed in this paper are based on the Boussinesq hypothesis, which implies that one of the Reynolds stresses is dominant over the other. For the complex separated flow in the experiment, it has been seen that both \(\overline{u^{\prime 2}}\) and \(\overline{v^{\prime 2}}\) are of the same order of magnitude, thus making the Boussinesq hypothesis invalid. However, also when removing this constrain, i.e., using the RSM model, the cross-wise fluctuations tend to be largely underestimated. It can be concluded that after the flow separation in the 1 st panel, the accuracy of the different numerical methods predicting the pressure on the panels does not depend so much on the robustness of the models as on fortune. On the other hand RSM seems to provide better estimations of the flow features, such as the wake shrink in the 3 rd panel, as well as a better overall performances in estimating the pressure difference on the panels, which in most of the cases is more conservative than what measured. This advantage could rely on the fact that RSM is not based on the Boussinesq hypothesis, thus being more appropriate for this type of flows. Nevertheless, it must be pointed out that our study has not coped all the RANS models available in literature. Additionally, the recent developments in numerical models and computational resources could take in a short time to better predictions of separated flows. One possibility could be, for example, the wavelet-based adaptive unsteady RANS model proposed by [PERSON] et al. (2018). **Author Contributions:** Conceptualization, P.F. and M.R. ; methodology, A.G., M.R. and P.F. ; software, P.F. ; investigation, A.G. and M.R. ; formal analysis, A.G.; writing--original draft preparation, A.G.; writing--review and editing, M.R. and P.F. All authors have read and agreed to the published version of the manuscript.