Volume I - Section IV - Experimental Work and Verification of CFD Methodology 
Page IV - 77 
4.2 CFD Simulations and Validation against Experimental Data 
4.2.1 Cage Condition 
A series of CFD models was constructed to simulate the cage wind tunnel experiments. The 
accurate modeling of the cage is an important stage in the project. In particular, the CFD cage 
model, as validated against the experimental data obtained in the wind tunnel, is used in the CFD 
animal research facility models as part of the racks. The two sets of boundary conditions that are 
of most concern are those associated with the transfer mechanisms into and out of the cage, 
namely the side cracks and the top of the cage, that includes the filter. 
4.2. 1.1 Description of CFD models 
All the models contained the same basic components and modeling philosophy: changes between 
the models reflected the different experimental procedures. 
The walls of the tunnel were specified to define the shape of the experimental wind tunnel. 
Typical CFD models for the tunnels are shown in figures 4.52 to 4.54. The ventilation system 
specification for the tunnel was the definition of a 0.4 m x 0.5 m (15.75” x 20”) opening at the 
entrance of the tunnel, and an extract at the opposite end. The size of the extract, 0.14m x 0.14m 
(5.3” x 5.3”), was defined such that the cross-sectional area was the same as in the physical 
situation. The mass flow rate set through the exhaust was varied to produce the same air 
velocities through the tunnel section as in the experiments, with the value dependent on the 
desired speed. The three screens and two filters in the tunnel were modeled using 0.4 m x 0.5 m 
(15.75” x 20”) planar resistances. The loss coefficients for each were set according to the free 
area ratio of the object. The values are listed below in Table 4.2.01, and are based on Idelchik 
(1989): 
Table 4.2.01. Free Area Ratios and Loss Coefficients Used for Tunnel Straightening Media 
Device 
Free Area Ratio 
Loss Coefficient 
Screen 1 
0.6 
2.00 
Screen 2 
0.4 
8.25 
Screen 3 
0.33 
14.35 
Filters 1,2 
0.5 
4.00 
The shelf on that the cage sits was defined as a rectangular block of dimension 2.5e-2m x 0.30 m 
x 0.50 m (1” x 1 1.8” x 20”). The shelf was located 0.10m (4”) from the floor of the tunnel for the 
parallel and perpendicular orientation experimental measurements, with the center of the shelf 
located at the center of the tunnel section. In the vertical orientation experiments, the shelf was 
located centrally within the tunnel. 
