Solving euler eq on unstructured grid: how do i transform the flux back...?
 

Hi all,
i am quite new, sorry if the title of my question is a little clumsy.
(if you give a better one i will correct it)

My problem looks simple, and i have already a working c++ program.
But there is just one thing that i cannot accept. :confused:

So there is the Euler eq.
We are on an unstructured grid. (Triangles.)
We solve it with the first order Euler method.

Therefore I need the divergence of the flux.
I transform my speed vector from my global coordinate system to the local coordinate system of one of the face of the given triangle.

What is the flux at the face?
I average the flux of the flux of neighboring triangles.
Then i take the normal component of the flux. (normal to the face)

And here is my question:

Do i have to transform the flux to sum it up over the 3 faces of the given triangle? How?
(Now i have a working code which only transform rhou end rhov back.)
(2 dimensional problem)

Thank you.