## 2 Materials and Methods
### Boundary Layer Wind Tunnel and Measurement Devices  
The experiments were carried out in a large boundary layer wind tunnel (BLWT) at ATB, Germany. The BLWT was specially designed to investigate ventilation and dispersion processes in agricultural buildings [34; 35; 36; 37], and has also been used to generate datasets for CFD validation [38; 39; 24]. The wind tunnel is 28.5 m long, consisting of an air inlet fitted of honey combs, an air outlet equipped with an axial fan, and a 19.5 m-long test section. The cross-sectional area of the test section is 3 m (width) \(\times\) 2.3 m (height). A combination of six spires and roughness elements was used to create a boundary layer flow. The spires were installed at the entrance of the test section. The roughness elements consisting of two sizes of right-angled steel brackets, with dimensions length \(\times\) width \(\times\) height of 0.010 m \(\times\) 0.004 m \(\times\) 0.004 m and 0.004 m \(\times\) 0.002 m \(\times\) 0.002 m for small and big brackets respectively, were arrayed in staggered rows downstream the spires. The total length of the roughness elements was 9.6 m with 0.2 m space between each row. The 1:50 scaled pig building model was placed at the symmetry line of the wind tunnel at 1.2 m downstream from the roughness elements. The model was oriented with sidewall openings perpendicular to the approaching flow and the outdoor yard at the downwind side. The blockage ratio of the scaled model to the cross-section of the wind tunnel was 0.8%, which is far less than the recommended maximum value of 5% for wind tunnel tests in VDI-guideline 3783/12 [40], and thus the tunnel effect can be neglected. Figure 2 shows photographs of the wind tunnel with the scaled model placed inside.  
The free stream wind speed at the wind tunnel inlet (\(U_{\mathit{inlet}}\)) was measured using a Prandtl tube, connected to a pressure transducer MKS Baratron(r) Type 120A (MKS Instruments, Andover, USA). The Prandtl tube was located at the centre of the entrance of the test section at a height of 1.3 m from the wind tunnel floor. Air velocity and turbulence around the scaled model were measured using a 2D fibre-optic Laser Doppler Anemometer (LDA) (Dantec Dynamics, Skovl  
Figure 1: Sketch of the 1:50 scaled pig building model. (**a**) Front view with different slopes of the roof above the exercise yard; (**b**) top view of the scaled model with 15\({}^{\circ}\) roof slope.  
with the BSA Flow Software package (Dantec Dynamics, Skovlunde, Denmark). The LDA probe head was 0.06 m in diameter and 0.45 m in length and provided a focal length of 0.25 m. The LDA probe was mounted on a three-dimensional computer-controlled traverse system that allowed automated and precise probe positioning with an uncertainty of <0.1 mm. A fog generator Tour Hazer II (Smoke Factory, Burgwedel, Germany) was placed at the wind tunnel inlet to produce seeding particles for LDA measurements. The temperature, relative humidity, and static pressure of the ambient air were measured using a FIAD 46x sensor with ALMEMO(r) D6 plug (AHLBORN Mess- und Regelungstechnik GmbH, Ilmenau, Germany). The data were sampled approximately every hour. The mean values of temperature, relative humidity, and static pressure for each day were used to calculate the air density, and therefore to calculate the \(U_{inlet}\) by using together with the data from the Prandtl tube.