# Experimental Assessment of RANS Models for Wind Load Estimation over Solar-Panel Arrays
## 1 Introduction
This study showed that the the front panel always experiences the maximum loads, but the wind direction may affect the loads on the following panels. Although single-panel studies provide relevant design information, the array configuration has been found to strongly modify the load distribution. [PERSON] and [PERSON] [17] demonstrated experimentally that the front panel in an array absorbs less force than the equivalent isolated panel, and that the subsequent panels receive loads which depend upon the pitch ratio. [PERSON] et al. [18] conducted an experimental study to investigate the pressure field on the upper and lower surface of a single panel. The separation between panels has an influence on surface pressure field, specifically the one of the front panel, but the orientation of the panel relative to the wind also plays a role in altering the influence of panel distance on the surface pressure field. [PERSON] et al. [19] performed an experimental campaign with parabolic troughs collectors protected by windbreaks (solid wall and porous fence). They concluded that with the appropriate selection of design parameters it is possible to reduce the aerodynamic loads (mean and peaks values) up to 60% over the first row of parabolic troughs collectors. Even if RANS simulations still represent the backbone of flow modelling in industrial applications, they are severely challenged in scenarios like the one that is object of the present study, i.e., turbulent/transitional flows with with flow separation and reattachment [21]. Currently, transition SST and SST \(k\)-\(\omega\)[22; 23; 24] are the RANS closure model more frequently used to simulate this type of flows. Three-dimensional steady RANS models, like \(k\)-\(\epsilon\), have been used to obtain mean wind-velocity pattern [25]. The assessment of the uncertainty produced by these models, however, has not been thoughtfully discussed for panels-array problems. As an example, a similar discussion has been tackled by [PERSON] et al. [26] for the transonic flow over an airfoil, using wind-tunnel data as a reference. The objective of present work is to assess the modelling capabilities of different RANS models to estimate the wind loads over solar-panel arrays. Provided that the typical angle of attack of the panels with respect to the wind is sufficiently large (which is often the case for solar-panel arrays, with typical inclination of 45\({}^{\circ}\)), an experimental campaign in a wind tunnel has been carried out on a simplified mock-up of a solar-panel array with the purpose of providing a solid experimental dataset, assessing the robustness of RANS models in such scenario. The Reynolds number based on panel-chord length is \(4.0\times 10^{4}\). The panel array configuration and boundary conditions that have been used in the experimental setup have been reproduced in the numerical simulations performed with the selected RANS models. The paper is organized as follows. After describing the experimental set-up and the post-processing techniques in Section 2, the numerical models are summarized in Section 3. Section 4 shows the main experimental and numerical results and a discussion on their comparison. Finally, in Section 5, the main conclusions of the study are presented.