UDF for fuel injection
 

Hi everyone,
Am new to Fluent and as well as to developing UDF's. Now am required to develop UDF for fuel injection at the inlet. Inlet has been selected as mass flow inlet in boundary types in Gambit. Once the fuel is injected, the inlet should be changed to a solid wall. Additionally, when the fuel is being injected only the fuel orifice is to be selected as mass flow inlet with the remaining part being a solid wall. And I need to develop a UDF for this condition. I've written a UDF and I need to know what needs to be changed and how far it is right.
'D' is the orifice dia and since am considering axisymmetric (with co-ordinates r,Z) its 'D/2'.

/* UDf for fuel injection at the inlet */
#include "udf.h"
DEFINE_PROFILE (mass_flow_rate, thread, position);
{
real r, D;
real x[ND_ND];
face_t f;
thread *t;
domain *d;
d=Get-domain(1);
if (r<D/2)
begin_f_loop(f, thread)
{
F_CENTROID (x, f, thread);
F_PROFILE (f, thread, position) = Rho*volume/time;
}
end_f_loop(f, thread);
else
F_PROFILE (f, thread, position) = 0;
}

Thank u, guys.