Laminar Anisotropic Flow - Acetic Acid in Water Is Not Diffusing
 

Acetic acid in water is not diffusing for an anisotropic laminar flow simulation. The model is a 200 m x 200 m domain. The viscous models are laminar and species transport. The fluid materials are acetic acid and water. For the anisotropic UDS diffusion the matrix components for XX and YY are 3 and 1, respectively. The diffusivity is 31.5 kg/m-s. The boundary condition type for each wall is outflow. The user-defined function for the initialization of the flow follows.
/************************************************** *********************
UDF for initializing contaminant distribution
************************************************** **********************/
#include "udf.h"
DEFINE_INIT(init_distrib_anisotropic,d)
{
cell_t c;
Thread *t;
int i;
real xc[ND_ND];
/* loop over all cell threads in the domain */
thread_loop_c(t,d)
{
/* loop over all cells */
begin_c_loop_all(c,t)
{
C_CENTROID(xc,c,t);
C_YI(c,t,0) = (1.0/4.0/3.141593/120.0/sqrt(0.09)/sqrt(0.03))*exp(-1.0*pow(xc[0] - 99.75,2.0)/4.0/0.09/120.0)*exp(-1.0*pow(xc[1] - 99.75,2.0)/4.0/0.03/120.0);
}
end_c_loop_all(c,t)
}
}
After running the simulation for ~ 980 seconds the diffusion is virtually unchanged. Why is the acetic acid not diffusing in the water? What am I setting up incorrectly?
Thanks,
Lisa