No-slip B.C.

Jing_min · June 21, 2013, 12:02

Dear All
Hello

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?

Thanks

Waldheri · June 25, 2013, 11:07

What do you mean with "bounce-back"? It does not sound like a no-slip boundary condition (which would set the velocity of the fluid to the velocity of the wall). So either your wall is moving or you are not applying your boundary condition (all components of the velocity vector to zero) correctly.

michujo · June 26, 2013, 04:54

Hi.

Is your code cell centered or vertex centered? If the velocities you are plotting correspond to those at the center of the first row of cells above the wall then they do not need to be zero, velocities are only zero at the wall (at the bottom boundary of those cells). Did you check if your velocity field is divergence-free?

Cheers,
Michujo.

June 21, 2013, 12:02	No-slip B.C.	#1
Jing_min New Member Jing Join Date: Dec 2011 Posts: 20 Rep Power: 14	Dear All Hello 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? Thanks

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June 25, 2013, 11:07		#2
Waldheri New Member Wouter Join Date: Jun 2013 Posts: 1 Rep Power: 0	What do you mean with "bounce-back"? It does not sound like a no-slip boundary condition (which would set the velocity of the fluid to the velocity of the wall). So either your wall is moving or you are not applying your boundary condition (all components of the velocity vector to zero) correctly.

June 26, 2013, 04:54		#3
michujo Senior Member Join Date: Dec 2011 Location: Madrid, Spain Posts: 134 Rep Power: 15	Hi. Is your code cell centered or vertex centered? If the velocities you are plotting correspond to those at the center of the first row of cells above the wall then they do not need to be zero, velocities are only zero at the wall (at the bottom boundary of those cells). Did you check if your velocity field is divergence-free? Cheers, Michujo.