normal temperature gradient on a boundary
 

Hi,

I impose temperature on my wall.
After convergence, I would like to post process my results :

I would like to get normal temperature gradient on a boundary and on a surface (plane created in fluent with surface => plane tools)
C_T_G macro is not adapted because it gives celle temperature gradient and my surface is constituted by facets
but F_T_G doesn't exist.

How can I manage ?
I shall be very grateful if you would take a little time to look at it...

Best regards, Sandrine.