No-slip B.C.

Dear All

I have simulated a simple channel with LBM.

At the bottom of the channel, I applied the No-Slip B.C., i.e. bounce-back.

As far as I know, at this boundary, the velocity is zero. But the vectors show that it is NOT.

How do you explain this?



Actually, bounce-back (with BGK) doesn’t give you perfect non-slip. It predicts an (unphysical) numerical slip at the wall (see Ginzbourg and Adler 1994 and He, Zou, Luo and Dembo 1997). However, in planar force driven channel flow the vertical velocity is zero (the flow is essentially one dimensional).

In addition to what Tim said, remember that the bounceback BC is supposed to give a no-slip condition u=0 halfway between the fluid node and the bounceback wall node. Even so, I suspect that there could be a small bug somewhere in your code, since the velocity doesn’t really seem to diminish close to the bottom.