dispersion of toxic material in road tunnel(species transport without reaction)
 

hello friends
I am doing my masters project on dispersion of gas in tunnel(2D) of 1000m. The gas is released from .1949m hole with mass flow rate of 900 kg/s at the middle of tunnel which is at 500 m. Ventilation is of 1m given at 100m apart. Means four ventilation at the left of the hole and four at the right of the hole.
Solver: Pressure based
unsteady state

Model : k-epsilon turbulence model
species transport without reaction(buoyancy effects are considered)
Boundary conditions:
Mass flow inlet : release source(hole)
pressure outlet : outlet
pressure outlet : ventilation

specification method is intensity and hydraulic dia.

problem is i have to make forced ventilation, even at natural ventilation gas is not moving out from ventilation with such a high flow rate. i am not sure about the boundary condition of the ventilation. how to make forced ventilation? What should be the boundary conditions.

Friends please reply its really urgent. Any response is welcome.