# Experimental Assessment of RANS Models for Wind Load Estimation over Solar-Panel Arrays
## 4 Results
### Mean Velocity Field
Nevertheless, the \(k\)-\(e\) model produces the most similar result to the experimental one, since the region of negative mean streamwise velocity is more extended than in the other simulations. The four numerical model predicts that the flow impacting the 2 nd panel has a negative mean streamwise velocity, suggesting that suction is occurring at the front side of the 2 nd panel. It is not possible to verify from the experimental velocity fields if the flow on the 2 nd panel has positive or negative streamwise velocity component, since this region is masked by the panel support. As the flow passing below the 1 st panel approaches the 2 nd panel, it is partially diverted upwards, producing an increase of vertical mean velocity above the bottom corner of the 2 nd panel (\(x/c\approx 2\)). In the region above the top corner of the 2 nd panel the vertical mean velocity changes its direction, reaching \(-0.5~{}U_{\infty}\). The behaviour showed by the numerical simulations is similar, but it is characterized by lower magnitudes in the vertical velocity. This is compatible with the different behaviour of the gap flow which has already been pointed out before: in the experiments the flow passing below the panels reduces its streamwise momentum, thus, due to continuity, part of the flow must be redirected upwards; in the simulations, which show much less streamwise momentum reduction, the flow passing in the space between the panels is less intense. The experimental result shows that the flow leaving the 2 nd, 3 rd and 4 th panel is accelerated vertically, upwards in the bottom part and downwards in the top part. The flow passing between these panel is, on average, directed upwards, thus suggesting that part of the mass flow is ejected towards the region above the panels, being unable to pass below the panels due to the loss of streamwise momentum. This behaviour is not correctly reproduced by any of the numerical models. The RSM result shows a strong downward velocity in front of the 3 rd panel which is only partially compensated by an upward acceleration of the flow above the panel. In the experiments the region over the 3 rd panel is partially masked, but it can be seen that the flow leaving from the top corner has the same magnitude and direction, suggesting that a similar upward flow could be present on the panel. The downward flow produced before the 3 rd panel by the RSM can be assumed to be the cause of the local reduction of the streamwise velocity in the region above the 3 rd panel and of its increase below it, due to the fact that part of the mass is redirected towards the gap flow. At the same time, the additional mass passing below the 3 rd panel is expelled again when the flow reaches the 4 th panel, producing an intense peak of upward velocity on the lower corner. Similarly, the transition SST model predicts a downward velocity before the 4 th panel, followed by an almost as strong upward velocity on the panel itself. The other models, instead, predict no relevant vertical velocity between the panels, suggesting no communication between the regions above and below the panels after the 2 nd one. The behavior of the flow between the panels has a strong effect on the wake topology. The measured thickness of the turbulent wake in the experiment is around \(1.5~{}c\), with a characteristic shrink corresponding to the 3 rd and 4 th panels, in which the width is reduced to \(1.25~{}c\). This shrink is likely produced by the injection in the upper region of momentum removed from the gap flow running below the panels. The turbulent wake in \(k\)-\(e\) and SST \(k\)-\(\omega\) models has the same thickness, but with a constant thickness over all the panels. The turbulent wake predicted by transition SST model is slightly thinner than the measured one. RSM predicts a turbulent wake with the same thickness obtained in the experiment, but it only predicts the shrink corresponding to the 3 rd panel.