## 4 Single Slot Analysis  
The numerical simulations were performed initially on a single slot configuration in order to calibrate the turbulence model by comparing the numerical data to the experimental measurements [12]. This analysis supports the understanding of the main flow dynamic phenomena that occurs in a slot impingement. Only H/B = 8 was considered for this scope, while different jet-walls distances will be analyzed for the multi-slot jet case.  
In Figure 6 the convective heat transfer coefficient distributions obtained by the different turbulent models were compared to the experimental values.  
The realizable k-\(\varepsilon\) and the SST turbulent models can predict the trend of the convective heat transfer coefficient with good accuracy with respect to the experimental measurements, while a notable discrepancy has been found with the v2f model. In the latter case, the largest difference occurs close to the area where streamlines have the highest curvature. For this reason, this model appears less suitable for the slot impingement application; unlike the other two RANS models; the percentage errors with respect to the experiments are reported in Table 1.  
The most accurate model with reference to the experimental data is the k-\(\varepsilon\) (error below 1% on the average value of the heat exchange coefficient). The maximum peak (concerning the jet axis) is slightly underestimated by this model. However the SST model also offers a good match in the average value, but it lacks accuracy in the prediction of the  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Model** & **Error on the Mean Value [\%]** & **Error on the Maximum Value [\%]** \\ \hline Realizable k-\(\varepsilon\) & 0.72 & \(-\)5.76 \\ SST & 4.54 & 16.43 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Percentage errors with respect the experimental measurements for the single slot case with H/B = 8, Re = 1.1 \(\times\) 10\({}^{4}\).  
Figure 6: Comparison between the numerical results and the experimental values [12] on the convective heat transfer coefficient, for H/B = 8, Re = 1100.  
maximum value (overestimated by 16.43%). In Figure 7 the velocity contours of the slot jet are reported for H/B = 8 with the k-\(\epsilon\) model.  
For this jet-wall distance the flow can interact with the surrounding stagnant fluid, which is transported by viscous effects on the edge of the jet. Near the impact to the surface, due to the higher static pressure gradient in the stagnation region, the flow bends and forms the wall jet region; here the boundary layer develops along the jet-axis distance. Moreover, within this zone there is an acceleration of the flow (orange colors), that starts with a velocity peak near the wall (when the boundary layer is not developed) and then gradually lowers, due to the boundary layer thickening. In Figure 8 the corresponding turbulent kinetic energy contour is shown to discuss the heat transfer.  
It can be noted that the maximum generation of turbulence kinetic energy is located where the flow from the opening is mixed with the surrounding stagnant fluid and forms a shear layer. In the stagnation zone there is the maximum heat exchange coefficient; here the boundary layer is not yet developed and does not interact with to the flow close to the surface. Near the wall jet there is a flow acceleration and a stronger interaction with the surrounding stagnant gas that supports more significant turbulent kinetic energy production.