Hi,

I just started to work with Fluent. I am trying to model a 2D axisymmetric problem.

The simulation is transient conduction (material has constant conductivity and heat capacity), and a heat generation that is a function of temperature.

Boundary conditions:

Bottom edge is adiabatic, sides have free convection, and top edge has constant heat flux. 

For the heat generation, I interpret the following UDF:

#include "udf.h"

DEFINE_SOURCE(ecomb,c,t,dS,eqn)

{

real source;

real temp = C_T(c,t);

int A = 29.8e18;

int B = -12779.78;

source = A*exp(B/temp);

dS[eqn] = -A*B*exp(B/temp)/(temp*temp);

return source;

}

I have tried the following without success: refine the mesh, lower the timestep or the relaxation, hybrid initialization (with very low courant), and initialize with temperature higher than ambient.

Any ideas what could be the cause?