I am trying to simulate the dilution of methane with air in a tunnel where both comes from different sources and mixes in the tunnel. But when I do VOF for the above simulation to obtain the volume fraction of methane in tunnel at different location I find that methane moves along the floor. Methane being a lighter gas is supposed to moved along the roof and moreover methane is not getting diluted with the air.
Why is this happening?
I have attached an image in which u can see that the methane is not getting diluted and it comes even to the floor instead of staying only along the roof