Boundary condition for open flow

Good day,

I plan to do simulation for an open flow around an obstacle. Can anyone guide me what is the suitable boundary condition at inlet, outlet, bottom and top boundary. I found the source code for channel flow (openLB) but i dont know how to modified it to make it an open flow boundary. It would be more helpful if someone could give me the source code.

maybe I do not exactly understand what you mean by “open flow”. But I guess it is the situation when velocity derivatives normal to the outlet of your geometry a zero. Am I right?

Then it is equivalent to impose a von Neumann BC. You can find more details here

I hope this will help you.