I was studying the scenario that the room with fire connected with a high and long narrow space with geometry size 30m(L)x1.6m(w)x40m(H), where the top, bottom and long sides are connected to the outspace. I defined those openings as pressure boundary conditions. The room opening is connected at somewhere of long and high side wall. The problem is that before the heated air flow into this narrow space, the airflow velocity has increased to extremely large values within a few time steps. I think it's result of pressure boundary at four side of domains (top, bottom, left and right). But how to prevent such problem?

Hi,

I don't know if you used the ENVIRONMENTAL PRESSURE option for your pressure boundary. This option is most suited for the openings like a window.