Question

Non-orthogonality creates a problem in _________ of the steady-state diffusion equation.

(a) the neighbouring terms

(b) the source term

(c) the direction of the surface vector

(d) the magnitude of the surface vector

I have been asked this question during an interview for a job.

Question is taken from Diffusion Problem topic in division Diffusion Problem of Computational Fluid Dynamics

Answer 1

Right choice is (c) the direction of the surface vector

Best explanation: The surface vector and the vector joining the owner and the neighbouring elements are not collinear for non-orthogonal grids. Thus, non-orthogonal grids need special attention in the steady-state diffusion equation.