density change with pressure
 

Hi everyone
I modeled a gas flow in a pipeline.because of the lack of availability of proper boundary condition in outlet I should use outflow boundary condition in outlet, so i have to use incompressible model and in fact the flow is incompressible.so I can't use ideal gas model and choose floating choice in operating condition.but because of the high pressure change in the pipeline I should verify density change with pressure.all of fluent models for changing density in material tab is are functions of temperature.so I wrote a udf for density changing with pressure and i interpreted it and there was no problem.but when I run the program, it stops in first iteration and shows the following error:

Error: Floating point error: invalid number
Error object: #f

and this is my udf:

#include "udf.h"

DEFINE_PROPERTY(cell_density, cell, thread)
{
real ro;
real press = C_P(cell, thread);

ro=1.8495e-6*press;
return ro;
}

the inlet pressure is 1723689 pa.

I will be really thankful if anyone could help me with this problem

just to be sure this is not the problem, can you try to compile it? sometimes, interpreted UDFs does not work properly.

I compiled the udf and tried to run the program but again there was the same error.

is there any other idea or anyone else who could help me with this problem??