Volume I - Section IV - Experimental Work and Verification of CFD Methodology 
Page FV - 89 
4.2.2 Calibration of CFD Diffuser model against Manufacturers Data 
When a diffuser is modeled using CFD it is essential to calibrate the model against 
manufacturer’s data. This is essential because small details in the geometry of the diffuser, the 
method of construction, etc., can change the jet characteristics. Of course, the detailed geometry 
of the diffuser could itself be modeled, but the level of detail required in full room models would 
make the model computationally impractical. This calibration allows the modeler to identify the 
jet characteristics close to the face of the diffuser where they can be expected to be virtually 
unaffected by room conditions. The three diffuser types were: a radial diffuser; a slot diffuser; 
and a low induction diffuser. 
4.2.2. 1 Radial Diffuser 
The diffuser is so named because it is designed to provide an airflow pattern that spreads in a fan 
shaped (or radial) fashion perpendicular to the center line of the diffuser as demonstrated in 
figure 4.6 1 . The intention of this is to prevent the formation of recirculation zones either side of 
the diffuser that could potentially retain contaminants. For this reason, this type of diffuser/flow 
pattern has become increasingly popular in animal rooms, was chosen for the base case whole 
room simulation, and was used in the experimental empty and populated room scenarios. It 
should be noted however, that the sideways throw characteristics could be compromised when 
strong thermal effects are present. 
The radial diffuser used in these simulations is as manufactured by Krueger (known in their 
literature as a TAD, total air diffuser) is shown in figure 4.60. The manufacturer’s test facility for 
this diffuser measured 3.66m (12’) x 3.66m (12’) x 2.74m (9’) high. The diffuser is located 
centrally in the ceiling of the test room. Two 0.30m (1’) high exhausts are located at floor level. 
The manufacturer’s data indicated the vertical and horizontal distance of the 0.25m/s (50 fpm) 
throw isovel (line of constant velocity) from the diffuser, that was used in the validation exercise, 
for various flow rates. 
In the CFD representation of the test facility, advantage was made of symmetry: the right side of 
figure 4.61 represents the symmetry plane. The flow rate that was chosen from the 
manufacturer’s data for validation purposes was that nearest the base case flow rate through a 
single radial diffuser. In particular, the base case flow rate was 270 cfm, while the nearest 
manufacturer’s data point is for 300 cfm. Further, the effect of temperature was also considered. 
The data point chosen was for a 2.8 °C (5.0 °F) rise in the air temperature between the discharge 
and the exhaust. Heat sources were applied to the walls of the CFD model to provide such a 
temperature rise. 
Figure 4.61 indicates that the CFD representation of the radial diffuser matches the location of 
the vertical and horizontal 0.25m/s (50 fpm) isovel data very well. Confidence can therefore be 
placed in the representation of the CFD radial diffuser in the animal facility simulations. 
