## 3 Results
### Flow and Pollutant Transport in the Reference Case (Case 1)  
Figure 6a shows the modeled airflow distribution in the cross-section across the thighs of the manikins in the fourth row when adopting the symmetric, upright seat layout. The airflow from the air-supply inlets in both sides of the aircraft cabin swept the ceiling and then travelled down in the aisle. Two large vortices in the cabin were formed with relatively low speeds in the respiratory zone of the passengers seated in the middle and aisle seats. Part of the airflow in the aisle went outward above the thighs and flowed upward. The other flow swept the floor and went to the air exhaust. With a symmetric geometry setting in the reference case, the computed airflow was nearly symmetric. The flow in the cross-section was relatively strong, which would aid in exhausting the pollutants but also result in cross-contamination. Figure 6b shows the airflow distribution in the longitudinal section across the center of seat 4B. The airflow mainly flowed upward due to the flow recirculation, blocked by the upright seats, and the thermal buoyancy, as shown in Figure 6b. The velocity magnitude near the passengers in the longitudinal section was generally smaller than 0.3 m/s.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Velocity** & **Concentration** \\ \hline Validation in this study & 0.396 & 0.481 \\ Validation in the literature [13] & 0.455 & 0.551 \\ \hline \hline \end{tabular}
\end{table}
Table 6: The RMSE discrepancy between the measurement and the CFD modeling for the velocity and particle concentration.  
Figure 6: _Cont._  
To assess the pollutant spread and possible exposure, the discrete pollutant source was hypothetically set to passenger 4B and 4E, respectively. Figure 7a shows the modeled steady-state, averaged normalized pollutant concentrations in respiratory zones of different passengers for the source at 4B, and Figure 7b is for the pollutant source at 4E. The red arrow in the figure designates the pollutant source location. The pollutant spreading region was concentrated in two rows in front of and two rows behind the source, as shown in Figure 7c,d. The pollutant concentrations near the source were generally higher. The concentration in the half cabin where the pollutant source was located was also higher than that in the other half cabin without the pollutant source. This was due to the formed air curtain in the aisle as shown in Figure 6a. With a symmetric seat arrangement, the pollutant spread between sources of 4B and 4E was quite similar. The above results were used as the reference benchmark when changing the seat arrangements in the following investigation.  
Figure 6: The modeled airflow distributions in Case 1: (a) airflow field in the cross-section across the fourth row, (b) airflow field in the longitudinal section across the \(\text{B}^{\text{th}}\) column.  
Figure 7: Normalized pollutant concentrations: (a) in respiratory zones of passengers in different seats for pollutant source at seat 4B, (b) in respiratory zones of passengers in different seats for pollutant source at seat 4E, (c) concentration distribution on a horizontal plane of the passenger’s nostril height for pollutant source at seat 4B, (d) concentration distribution on a horizontal plane of the passenger’s nostril height for pollutant source at seat 4E.