Question

The central differencing scheme becomes inconsistent when the Peclet number _____________

(a) is higher than 2

(b) is less than 2

(c) is higher than 5

(d) is less than 5

This question was posed to me during an interview.

My doubt stems from Convection-Diffusion Problems in section Convection-Diffusion Problems of Computational Fluid Dynamics

Answer 1

Right answer is (a) is higher than 2

Easiest explanation: When the Peclet number goes beyond 2, the central difference approximation fails. The discretization process becomes inconsistent here. In this case, an increase in the neighbouring value will lead to a decrease in the value at the central node.