I just started LBM, I have a few questions about the bounce-back boundary conditions:
the D2Q9 lattice is like this:
7 3 6
4 1 2
8 5 9
Let’s assume node 1 is on the left-top corner, and node 2 is on the top boundary.
For node 2, after streaming, f1,f2,f4, f3,f7,f6 are known, only f8,f5,f9 are unknown, so we can apply the bounce back rules to calculate f8,f5,f9 like:
f8=f6; f5=f3; f9=f7;
But for node 1, I THINK after streaming, we only know f3, f4,f7, because those distribution functions are coming from the neighborhood nodes, but how can I get f6, f8, f2, f5, f9? if I apply bounce back rules, I might have:
f5=f3;f9=f7;f2=f4; how about f8 and f6?