Versteeg Example Question
 

Dear all,

I am working on the example 5.1 of the Versteeg book (page 137-138). I am specifically looking at the central difference scheme. My question is: why are the boundary conditions for D_A and D_B = 2*\Gamma/delta x= 2*D?

Why the "2" and not just D_A=D_B=\Gamma/\delta x=D? I don't understand where the 2 comes from. Thanks.

Sorry but in my version of the texbook the example 5.1 is at page 106 and solves the 1D linear advection-diffusion differential equation, is that the problem you are solving?

Hello,
If you are dealing with the diffusion, then the 2 comes from the fact that the cv center of the boundary cell is at distance dx/2 from the center of the boundary face (for a cartesian grid). Thus diffusive flux read Area*(phi_b-phi_C)/(dx/2). After simple algebra, you get what you are looking for.

Thanks! I see it now.