When you do an integral over any quantity (cell or facet), you never evaluate the normal at an actual vertex. For getting a representation of the facet normal you can evaluate, you could look at: Obtain velocity normal to boundary - #2 by dokken
When you do an integral over any quantity (cell or facet), you never evaluate the normal at an actual vertex. For getting a representation of the facet normal you can evaluate, you could look at: Obtain velocity normal to boundary - #2 by dokken