http://d-scholarship.pitt.edu/23542/1/Lina_Xu_ETDpitt_2014.pdf

http://www.palabos.org/forum/read.php?9,7184

Hello Mr. Baghat,

Although bounce back BC's are simple, but implementing them in a right manner makes it complicated depending on the geometry of one's problem. So I suggest that read some concise and explanatory papers in this field. I send you one and hope that it would be helpful. But briefly I can say that if you update your BC before streaming step , so you are using half way BB. and if you updating BC before collision step you are using full way BB.

Best,

Sh.Gh

It is not entirely correct to say that the BounceBack is complex to implement depending on the geometry. The Full way BounceBack (FBB) is easy to implement and independent of geometry if it is implemented correctly. In contrast, the Half wat BounceBack (HBB) is considerably more difficult to implement, precisely because it is dependent on the geometry of the BC's. In other words, answering the question,

Characteristics of FBB:

1. - The boundary is located on the edge of the numerical mesh (the nodes that represent the walls).

2. - It is calculated later to the collision step, so it is independent of the geometry of the BC's.

3. - Numerical approximation of 1st Order.

4. - Considering a node immediately close to the boundary, the process starts at a time t in the collision step and ends at a time t +1 in the propagation step.

Characteristics of HBB:

1. - The border is located at an intermediate point between a node next to the solid wall and a node that represents this wall.

2. - It is calculated later to the propagation step, so it is highly dependent on the geometry. It can always be built in a general way by being ingenious.

3. - Numerical Approximation of 2nd Order.

4. - Considering a node immediately close to the border, the process starts at a time t in the collision step and ends at that time t in the propagation step.