## 3 Results and Discussion  
### Airflow Characteristics in and outside the NVD Building  
Figure 9 shows the steady state simulation results of airflow streamlines inside and around the NVD building for different opening combinations. Different airflow patterns were observed for different opening scenarios at the same reference wind speed (\(U_{\mathit{ref}}\) = 4.41 m\(\cdot\)s\({}^{-1}\)) which correspondence to inlet velocity 8 m\(\cdot\)s\({}^{-1}\). In all the cases, when the wind approached the building, most of the airstreams entered the building via the windward opening. The major part of the airflow stream either attached to the floor (Case 1, Case 3 to 5, and Case 7 to 8) or attached to the ceiling (Case 2 and 6) before leaving the leeward sidewall opening. A small portion of the airflow stream directly flowed out through the roof opening. The remaining air streams re-circulated either close to the floor (Case 2 and Case 6) or attached to the ceiling (Case 1, Case 3 to 5, and Case 7 to 8), created vortex and passed through sidewall and roof openings. For Case 1 SM with the middle part of both side walls opened, which is the case for the spring and autumn opening practices in the research barn Dummerstorf, the major jet approached directly towards the middle animal resting place (R2, as location shown in Figure 3b) while a small jet formed a vortex above the first animal resting place (R1, as location shown in Figure 3b). After passing above the resting places (R1, R2) and animal walking alley, major jet diverted at the wall of windward side of the feeding alley (FA, as location shown in Figure 3b). Then the air velocity became weaker when it touched the animal resting floors and walking alleys before leaving the leeward opening. This indicated that animals staying at the leeward side of the feeding alley may have less fresh air than those staying at the windward side. However, the animal comfort will be different depending on the jet of cold air [4] or warm air [33]. The small or weaker jets which could not go through roof opening created a recirculation zone below the windward roof. As seen from Figure 10, this vortex became smaller as the  
Figure 9: Airflow patterns inside and outside of the NVD barn for different opening combinations. The inlet velocity followed the profile described by Equation (1), and the reference profile velocity was 4.41 m\(\cdot\)s\({}^{-1}\) at the height of 0.1 m.  
approached wind became stronger. It is also found that the higher the wind speed approached the building, the higher the velocity of the jet entering the building. There was creation of recirculation zone just after the feeding alley (Cases 14 to 18). Additionally, a vortex formed above the leeward roof in all cases (Figures 9 and 10) though the size of the vortex depended on the approach wind speed and different opening combinations. In Case 2 SMT and Case 6 SMTB (Figure 9), the incoming air flowed upwards immediately after passing through the windward opening, and the air recirculation region consisted of low air velocities formed above the floor. This is probably caused by the bottom sidewalls that acted as guiding plates of airflows. The similar up-jet airflow pattern was also observed by [PERSON] et al. (2015) and [PERSON] et al. (2014) in naturally ventilated livestock barns for the cases with high bottom sidewalls. For the Case 3 SMB and Case 7 SMBD (summer practice in NVD at Dummerstorf), the strong jet attached to cow resting floors and walking alleys more in the windward sides than in the leeward side. The remaining jet circulation phenomenon was same as Case 1 SM except the size of the eddy and jet velocity was stronger above the feeding alley than the Case 1 SM. However, a strong influence on jet diversion by the wall of the feeding alley was found which was not considered in other studies ([PERSON] et al., 2017; [PERSON] et al., 2017), even though this diversion became more visible when the approaching wind became stronger (Figure 10).