For simulation of wind around buildings (urban air pollution) what's the correct bounday conditions?!

outflow or pressure-outlet?

I tryied both and results are almost the same. Sometimes the convergence process is better with the first and other cases it results better with the second bc. Soo, I am confused.

thanks for your help.

Since you get same results from both boundary conditions and both of them converge. You can use outflow boundary condition without any problem here. Actually, you can apply outflow BC only when your flow is fully developed at the outlet. So u need to be careful when you apply this boundary condition.

The primary difference between outflow and outlet conditions is that outflow is essentially a constant mass flow ratio condition but an outlet is a constant pressure condition. The flow weighting parameter decides what your ratio is when you chose outflow, critical if you have more than one outflow boundary.

Phil

Thanks Ragh and Seeker Phil, for your answers. It help me to better understand the figures.

Mike