Question

Consider the general discretized equation given by aP ΦP+∑F~NB(P)aF ΦF =0. Which of these statements is correct according to the opposite signs rule?

(a) aP and aF are of opposite signs

(b) aP and ΦP are of opposite signs

(c) aF and ΦF are of opposite signs

(d) ΦP and ΦF are of opposite signs

The question was asked in class test.

My query is from Diffusion Problem topic in portion Diffusion Problem of Computational Fluid Dynamics

Answer 1

Correct option is (a) aP and aF are of opposite signs

For explanation I would say: The boundedness property is enforced only when the coefficients aP and aF are of opposite signs. So, the opposite sign rule says that the coefficients of the flow variables ΦP and ΦF are of opposite signs.