Volume I - Section IV - Experimental Work and Verification of CFD Methodology 
Page IV - 79 
these cracks as planar resistances of height 6.4e-3m (V4”). Initially using the results of the series 
set base experiments, the values for the loss coefficients on the side cracks were varied until the 
predicted CFD values for the cage ACH reasonably matched the experimental data over a range 
of tunnel velocities for each of the three orientations. These loss coefficient values were then 
tested against the lower injection rate experimental series (series sets one to four, to eight) to 
ensure good agreement. Any adjustments to the loss coefficients were then tested over the a 
range of experimental data sets to ensure that the values were applicable to all possible 
conditions that the cage could be presented within the animal facility room environment. 
4.2. 1.2 Results from CFD Simulations 
In this section, variable plots from a typical cage will be considered, then the comparison of the 
CFD results with the experimental data will be presented. 
4.2. 1 .2. 1 Plots from Typical Cage CFD Simulation 
A single CFD simulation will be considered to indicate the physical features that can be 
predicted using CFD, which are otherwise difficult to determine using experimental procedures. 
In particular, the CFD allows the determination of flow patterns within the cage, as well as 
temperature and concentration distributions. 
The close-up plot of the vector field at the plane halfway through the tunnel for the Series Sets 
Six: Parallel Orientation, Heater On (SMO) 40 fpm (0.2 m/s) case is shown in figure 4.57. Note 
that the key accompanying the plot indicates speed in m/s (to convert to fpm, multiply by 200). 
Externally from the cage, the most prominent feature is the recirculation region immediately 
behind the cage. Internally, the main feature is the buoyant plume resulting from the SMO. 
However, it is noticeable that, apart from the plume, there are few flow patterns present within 
the cage of any great magnitude. In particular, although there is obviously strong external flow 
that is impinging directly onto the side of the cage, relatively small amounts of flow actually 
enter it. 
The equivalent close-up plots of the temperature and CO 2 concentration fields are shown in 
figures 4.58 and 4.59 respectively. Note that the keys indicate the temperature in °C and 
concentration in kg of species/ kg of air (to convert to ppm multiply by le6*(28.96/44)) 
respectively. The temperature plot shows the distinct plume resulting from the SMO. This plume 
dominates the distribution of the concentration also, as the CO 2 is entrained into this flow 
feature. The concentration plot also indicates the clear stratification of the CO 2 in the cage. That 
is due to the density difference between the CO 2 and air. This stratification makes the matching 
of the CFD results to the experimental data difficult, as relatively small spatial changes result in 
marked differences in the level of concentration. 
