DEFINE_UDS_FLUX(my_uds_flux,f,t,i)
{
cell_t c0, c1 = -1;
Thread *t0, *t1 = NULL;
real NV_VEC(psi_vec), NV_VEC(A), flux = 0.0;
c0 = F_C0(f,t);         //returns thread ID for cell c0
t0 = F_C0_THREAD(f,t);        
F_AREA(A, f, t);         //Area vector of a face
/* If face lies at domain boundary, use face values; */
/* If face lies IN the domain, use average of adjacent cells. */
if (BOUNDARY_FACE_THREAD_P(t)) /*Most face values will be available*/
{
real dens;
/* Depending on its BC, density may not be set on face thread*/
if (NNULLP(THREAD_STORAGE(t,SV_DENSITY)))
dens = F_R(f,t); /* Set dens to face value if available */
else
dens = C_R(c0,t0); /* else, set dens to cell value */
NV_DS(psi_vec, =, F_U(f,t), (F_V(f,t)-1.0), F_W(f,t), *, dens);
flux = NV_DOT(psi_vec, A); /* flux through Face ,(rho*u*psi)*/
}
else        
{
c1 = F_C1(f,t); /* Get cell on other side of face */
t1 = F_C1_THREAD(f,t);
NV_DS(psi_vec, =, C_U(c0,t0),(C_V(c0,t0)-1.0),C_W(c0,t0),*,C_R(c0,t0));
NV_DS(psi_vec, +=, C_U(c1,t1),(C_V(c1,t1)-1.0),C_W(c1,t1),*,C_R(c1,t1));
flux = NV_DOT(psi_vec, A)/2.0; /* Average flux through face */
}
/* Fluent will multiply the returned value by phi_f (the scalar's value at the face) to get the ``complete'' advective term. */
return flux;
}