Question

The diffusive fluxes in the inlet boundary conditions _________

(a) are specified

(b) can be calculated

(c) are not necessary

(d) should be approximated

I have been asked this question in semester exam.

This is a very interesting question from Boundary Conditions topic in section Boundary Conditions of Computational Fluid Dynamics

Answer 1

Correct answer is (d) should be approximated

Easiest explanation: The diffusive fluxes are usually not known. They should be approximated using the boundary values of the variables and one-sided finite difference approximations for the gradients.