## 3 Previous Wind Tunnel Studies on NVLBs
### The Flow Studies  
#### 3.1.1 The Effect of Openings  
One of the first published studies on the simulation of flow within a scale model of an NVLB in a wind tunnel was that of [PERSON] et al. [42]. They reported that there was no readily available information on airflow patterns in a naturally ventilated grower-finisher barn for different air inlet designs and windbreak panels. To obtain such information, they conducted smoke visualisation of isothermal airflow patterns for four air inlet types. The barn model was scaled down to 1:20, and the Reynolds number independence (Re \(>\) 3500) was observed from qualitative comparisons of flow patterns within the building. Although appropriate boundary conditions (relevant ABL characteristics) were not simulated, the study provided important insight into the impact of air inlets on airflow within an NVLB. For instance, they found that the windbreak panels create extra turbulence, especially for larger openings, which improved air ventilation within the building. [PERSON] et al. [43] demonstrated, using a model (1:20) of a finishing pig house with full-length openings at both sidewalls and without a ridge opening, that the height of the wall between the ventilation opening and the ceiling was the most important for the local air velocities within the building. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Approx. Const.** & **A** & **B** & **C** & **D** & **E** & \(\mathbf{f_{red}}\) \\ \hline [PERSON] et al. & 16.8 & 33.0 & 1 & 5/3 & 1 & \(\frac{fz}{U(z)}\) \\ [PERSON] and [PERSON] & 32.0 & 50.0 & 1 & 5/3 & 1 & \(\frac{fz}{U(z)}\) \\ [PERSON] & 4.0 & 70.78 & 2 & 5/6 & 1 & \(\frac{fL_{xx}(z)}{U(z)}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Approximation constants (A–E) and reduced frequency (\(\mathbf{f_{red}}\)), according to [PERSON] et al. [39], [PERSON] and [PERSON] [40], and [PERSON] [41]. Adapted from [32]. The impacts of different opening configurations and wind direction on the ventilation of a 1:60 scale model of a dairy cattle barn was studied by [PERSON] et al. [44] and [PERSON] et al. [45], respectively. Using hot-wire anemometry in their first study, [PERSON] et al. [44] observed that enlarging the opening height only at the inlet led to higher velocities at the outlet. They also observed that air velocities at the centre of the house were hardly affected by the inlet opening height. However, without the outlet wall, the velocities at the centre of the house were three to four times higher. In their second study, [PERSON] et al. [45] estimated airflow rates through the openings by multiplying the opening's free surface area with the average air velocity measured in the respective ventilation opening. They demonstrated that the estimated airflow rates through the inlet and outlet openings gradually decreased, in both scale models, with increasing wind direction. [PERSON] et al. [46] focused on the effect of opening configuration on indoor and outdoor airflow conditions and the ventilation rate of naturally ventilated buildings using the laser Doppler anemometry (LDA) and tracer gas methods, respectively. The measured velocity vertical profiles showed that different opening scenarios produce different magnitudes and directions of the streamwise velocity near the building floor. However, the main driver of this velocity behaviour was the inlet opening position, regardless of the outlet openings. If the opening position was near the bottom of the building wall, then a substantial downstream flow was observed near the indoor floor of the building. On the contrary, the upper inlets produce upstream and weaker flow at the floor. However, it was shown that while the location of openings does not have a significant impact on the air change rate, the size of the openings certainly has.