[Roby_1986]

Hi everybody,
I'm simulating natural ventilation in building, through the attached model.
I've imposed a velocity inlet on the front face of the parallelepiped, representing the air outdoor the building, and outlet pressure on its back face. Then the other face are set as simmetry, except the basis, which is a rough wall.
I want to evaluate the pressure coefficient on the building walls and the ventilation rate through the window on the frontal face of the building.
Now, the problem are two.
1. How to calculate The ventilation rate through the window, since I've tried with "Volume flow rate" as surface integral on the window face, but this value oscillates between negative and positive values during iterations. So, how could I calculate it (m3/s)?
2. After a first phase when residuals go down and seem to establish constant, a second phase starts, when residuals rise. I've monitored also the static pressure on the inlet face which seems to be quite constant, oscillating beetween -0.94 and -0.9 pascal.
What could be the reason?
Thanks a lot