[ansys_matt]

Hello,

I am trying to simulate methane combustion in a tank. To start, I set the model to species transport with an inlet bringing in a mixture of methane-air (the fluent database mixture) from one inlet. The tank is open on the other end which I set as an outlet.

My question is this: I set the Cell Zone Conditions to the methane-air mixture (a fluid). But after the solution is calculated and I check in cfd-post at the first time step, the concentration of both methane and O2 (in fact all species) are zero everywhere inside the tank until it starts coming in from the inlet!

Why is the concentration of all species zero when I set the cell zone conditions to be the methane-air mixture? It appears that the only methane (and the only 02) is coming in from the inlet as the solution moves forward in time. How can I begin the simulation with the methane-air mixture already inside the tank (and thus a non-zero species concentration from the start)?

I thought that is what the Cell Zone Conditions setting did??

Thanks.

[ansys_matt]

I edited my question so hopefully it is clearer.
Please help!

[ansys_matt]

Hello,

I solved this by using a UDF to initialize before solving. Here is the contents of the UDF, for future reference. This is run only once before the solution starts, so it simply sets the correct values in all the cells.

/***********************************************************************
   UDF for initializing species mass fraction.  
   Uses C_YI(cell_t,Thread,Spec. num)

   This UDF should be run before solution initialization.

      Species 0 is Methane (Mass Fraction)
      Species 1 is O2 
      Species 2 is H2O
      Species 3 is CO2
      Species 4 is N2
 ************************************************************************/
 
 #include "udf.h"
 
 DEFINE_INIT(my_init_func,d)
 {
    cell_t c;
    Thread *t;
    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) = 0.056;
                C_YI(c,t,1) = 0.22;
                C_YI(c,t,2) = 0.0;
                C_YI(c,t,3) = 0.0;
                C_YI(c,t,4) = 0.724;
           }
         end_c_loop_all(c,t)
      }
 }

[saeed110]

hi matt
thanks for your comment
how should i verify for fluent to know that, what is the species 1 or species 2?
thanks