[skumar112]

I am trying to implement a UDF to calculate the density of DPM droplets but for some reason this just returns the value 4230 every time

DEFINE_DPM_PROPERTY(density,c,t,tp,T)
{
real rho;
if (T < 385)
{
rho = (1 - TP_USER_REAL(tp,0)) * 4230 + TP_USER_REAL(tp,0) * (1053.73 - 1.2412*T + 2.27199e3*T*T - 3.764e6*T*T*T);
}
else
{
rho = (1 - TP_USER_REAL(tp,0)) * 4230 + TP_USER_REAL(tp,0) * 697;
}
return rho;
}

[obscureed]

Hi Skumar112,

Well, if TP_USER_REAL(tp,0) is 0.0, then 4230. is the correct answer in all circumstances. So perhaps you should check that TP_USER_REAL(tp,0) is behaving as you expected.

By the way, something is badly wrong with the polynomial in T: it returns values around -2e14 at T=385K.

One way to debug this kind of UDF is to pick one in every X visits to the UDF, and to print out all the steps in that visit's calculations, using Message to print to the Fluent window. X could be 10000 or 1000000 or whatever, depending on the size of the simulation. How do you pick one in X? -- one way is to define a "static int counter=0;" outside the UDF, and inside the UDF "if(++counter > 1000000) { counter=0; Message(...);}".

Good luck!
Ed