Calculation of face vaules with udf

rom

I have got a problem with the calculation of face vaules from cell center values. For an interior face i could caculate the face value either from the c0 cell side or the c1 cell side, using the cell values and the gradient. For a species it looks like this

from c0

face_value0=C_YI(c0,c0thread,i)+NV_DOT(C_YI_G(c0,c 0thread,i),dr0)

and from c1

face_value1=C_YI(c1,c1thread,i)+NV_DOT(C_YI_G(c1,c 1thread,i),dr1)

dr is the vector from cell center to the face center. Both face values should be identical but unfortunatly they are not. I tried it on a sturcured meshe with full converged soultion. Is there any other way to get consistent values for the faces?

Thanks for any suggestions

RoM