Question

The direction of the normal vector to a face in mesh ____________

(a) is from the owner element to the neighbour element

(b) is from the neighbour element to the owner element

(c) is in the direction of the flux

(d) is in the direction opposite to the flux

The question was posed to me during an internship interview.

This intriguing question comes from Numerical Methods topic in portion Numerical Methods of Computational Fluid Dynamics

Answer 1

Right choice is (a) is from the owner element to the neighbour element

To elaborate: The orientation of the faces is such that the normal vector to the face points from the owner element to the neighbour element. Depending on this the sign of flux term changes. Orientation does not depend on fluxes.