Hello everyone:
I have an old question, which has been mentioned many times in the earlier discussion. The problem is about the normal direction of an interior facet:
Assume \Omega_1=[0,0]\times [1,1] and \Omega_2=[1,0]\times [2,1], thus x=1 is an interface with facet id=1. Then, if we would like to calculate a flux
a = inner(u * n , v)('+') * dS(1)
where u is the trail vector function, v is the test vector function and n = FacetNormal(cell). As far as I known, n(’+’) and n(’-’) are chosen randomly.
I am wondering if there is any update for this issue? Is there any way to set n(’+’) to be the direction from \Omega_1 to \Omega_2 and n(’-’) is the opposite direction?
Thanks in advance,
Leon