Hi Daniel, you want to use the ‘ifield’ index that is 1 for velocity field and 2 for temperature field. Your usrbc subroutine would look like: if (ifield.eq.1) then YOUR BC FOR VELOCITY else YOUR BC FOR TEMPERATURE endif if you only solve for velocity and temperature fields. Marco On Jan 22fd, 2018, at 3:58 AM, [email protected]<mailto:[email protected]> wrote: Hi all, I'm trying to apply both temperature and velocity flux boundary conditions at one of my boundaries. I am unsure, however, how to apply this in userbc in the usr file. I can set one of the two by having an 'f' in the box file (for just one variable) and then defining 'flux =' in userbc. How do I do this for both temperature and velocity? Is there separate term for flux for temperature and flux for velocity? Best, Daniel Ward _______________________________________________ Nek5000-users mailing list [email protected]<mailto:[email protected]> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users