[Hooman]

Simple question:

When in upwind differencing of a convection problem we have:

if ro*u(w) > 0 then aW = max(F(w),0) and aE= max(0,-F(e))

what exactly do the terms in the brackets mean? I know that if the flow is in the positive direction then the face velocities are approximated as the upstream node velocities but what happens to the mass flux? what does the max and the min mean? Do they mean the maximum flux i.e. the fluxes at the upstream nodes? and what do the 0's in the brackets represent?

Also how are these evaluated at the boundaries? Is the mirror node interpolation method the kind of approximation used along with upwinding?

Please help!! This is killing me!

Thank you in advance.