## 3 Results and Discussion
### Numerical Results
Figure 18: _Cont._  
Previous research of our team concerning CO\({}_{2}\) accumulation in the crew quarters of the International Space Station [62] allowed us to define a breathing zone (BZ) for the occupant by applying Fast Fourier Transforms to the simulated periodic human breath flow. Later, in [52], using the same simulated breathing function, a comparison was proposed of breathing zone CO\({}_{2}\) concentration levels with and without a PV system to determine whether the impact of a lateral PV nozzle is noticeable in the breathing zone during a full breathing cycle. As mentioned previously, the positioning of the PV nozzle from the head/face of the virtual manikin in [52] is similar to the one in this study, however the body position is slightly different in this previous work (i.e., zero g neutral position). In this case the proposed definition of the breathing zone concerns zero gravity conditions-no buoyancy, no gravity influence on the CO\({}_{2}\) presence. In these particular conditions, the PV solution proved to be efficient, showing reduced CO\({}_{2}\) content in the breathing zone of the occupant across the whole breathing cycle. Although both the lateral PV solution and the general ventilation system alone were capable of removing the exhaled CO\({}_{2}\) from the BZ across a breathing cycle, closer inspection revealed a supplementary 8% reduction in inhaled CO\({}_{2}\) over each breath in the case of the PV system. In the current study, we implemented the same type of PV strategy (i.e., a lobed nozzle on a lateral diffuser). However, the present analysis represents the preliminary step within a more complex analysis. We did not take into consideration CO\({}_{2}\) emissions from breathing, for instance, nor did we simulate aerosols. Figure 19 shows close-up images of the distributions of velocity and temperature around the passengers with and without PV. The presence of the PV diffuser itself modifies the distribution of the thermal boundary layer of the passenger (Figure 18) at the head and torso levels. Because the thermal boundary layer in the frontal part of the torso and of the head partially intersect with the breathing zone, if the PV jet modifies the boundary layer (as seen in Figure 19), it follows that it will influence air distribution in the breathing zone as well. The degree to which this influence is manifest depends on the PV jet's initial velocity, as well as its orientation. This is illustrated in Figure 20, where we tried to put in evidence the interaction between the convective boundary layer of the human body and the PV flow with and without a PV diffuser. We superposed the frontiers of the breathing zone in front of the passenger (as defined in [62]) on the velocity and temperature fields. As visible in Figures 17-20, the boundary layer of each passenger develops around their bodies and is visible at the upper part of the shoulders and heads. In the transverse planes, the convective flows are also attached to the vertical surfaces of the seats extending towards the neighboring seat. In Figure 20b, in the region of the PV diffuser, higher values of velocity magnitude are observable, starting with a small region corresponding to the initial region of the low-momentum PV jet and developing further in what could be the interaction between the convective boundary layer and the farther region of the PV flow. In Figure 20c, the air-temperature distributions show that the small region corresponding to the potential core located in front of the face of the passenger is colder than its surroundings. This could be explained by the fact that the clean air issuing from the PV nozzle has not yet mixed  
Figure 18: Distribution of velocity and temperature inside the modeled domain in the case with personalized ventilation. Vertical planes passing through the passengers placed in the second row (A) and PV (B); 1, 2—transversal direction. Vertical plane passing through the breathing zone: D.  
with the ambient air, thus fulfilling its objective.