## 3 Results and Discussion  
The simulation described above was performed on the Intel(R) Core(TM) i7-8700K [EMAIL_ADDRESS] GHz computer (6 cores, 64 GB RAM). In this section, the simulation results are compared with the ones reported in [18], where the results were validated in regard of the time-averaged airflow velocities within selected time intervals where the airflow velocity was considered to be stabilized. In [18], a very good agreement of simulated and experimental results was reported for the velocities measured by the grid anemometers; however, a relatively lower accuracy was observed for velocities measured by the tunnel anemometers. The improved model and validation procedure described in this paper can be characterized as follows:  
* More suitable representation of tunnel anemometers in the improved model better corresponds to the actual measurement of airflow velocity in the Polana tunnel (in [18]; the measurement by the tunnel anemometer was represented as a two-point measurement of the airflow velocity on both sides of the tunnel).
* Improved evaluation procedure considers:
* Time intervals, where the airflow is considered to be stabilized, of the same length (in previous evaluation they had various lengths [18]);
* The same number of values is taken into account for all ventilation modes (in [18], different frequencies of the velocity values recording for experimental data and for the simulation were considered);
* Extended evaluation of average velocity values.  
The analysis focused on the airflows generated by the three operation modes of ventilation operation (modes 1-3) during which the ventilation relatively soon created a stabilized airflow, the velocity of which was measured by the grid and tunnel anemometers. The average airflow and time-averaged airflow velocities at selected time intervals, where the airflow velocity was considered to be stabilized, were calculated. For the three individual ventilation modes, the 6 min time intervals 900-1260, 2760-3120 and 5390-5750 s were considered. We noted that although the Mode 1 ventilation scenario was used to set up the model's parameters, in the following section, we include it when evaluating the simulation results as well, due to completeness.  
\begin{table}
\begin{tabular}{l l} \hline \hline FDS version & 6.5.2 \\ \hline MPI version & 3.0 \\ \hline MPI library version & Intel(R) MPI Library 5.1.3 \\ \hline Simulation mode & LES \\ \hline Turbulence model & Deardorff (default) \\ \hline Boundary conditions & OPEN for the right tunnel portal, OPEN with specified dynamic pressure for the left tunnel portal, CONCRETE1–2 for tunnel walls and road, INERT for details of tunnel equipment (vertical traffic signs, jet fans shroud) and material, filling the computational domain up to its boundaries \\ \hline HVAC settings & VOLUME\_FLOW of 19.75 m\({}^{3}\)/s, AREA of 0.54 m\({}^{2}\), jet fan dimensions of 0.9 \(\times\) 0.6 m, jet fan shroud length of 3.9 m, linear jet fan onset of 115 s \\ \hline Meteorological conditions & Temperature inside the tunnel of 6 \({}^{\circ}\)C, temperature outside the tunnel of 5.5 \({}^{\circ}\)C \\ \hline Gas phase reaction & POLYURETHANE\_REAC, SFPE Handbook, GM27 \\ \hline Simulation duration & 7180 s \\ \hline Stability conditions & Based on velocity norm (default) \\ \hline Time step & Variable, typically 6 \(\times\) 10\({}^{-3}\) s for active jet fans, CFL 0.08 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Main simulation settings.