[Anne009z]

Hallo, and thank you for your time.
I am new to the simulation of species transport, and i have run into some troubles explaning the results.

The case is a tunnel with an inlet and outflow in each end. There are mechanical fans in the cieling. I have activated the species model and completed the mixture-template.

The species is supposed to be released constant from the floor, so i have activated the species boundary condition and enteret the species mass fraction.

When i start the simulation, and obtain the results for the species concentration i the tunnel, my guess would be that the species concentration in the tunnel would decrease when increasing the amount of air passing trough the tunnel.

In fact my average species concentration inside the tunnel increases when increasing the amount of air passing through the tunnel.

I have a hard time explaning this, and can't really figure it out, from reading the litterature and online discussions regarding this. I think it has something to do with the convection/ diffusion equation, but can't really explain it.
Please help,

I have attached a picture of the geometry of the tunnel, and a picture of a graph showing when i add more air into the tunnel, from the mechanical fans, the species concentration increases

https://ibb.co/egOcjG

https://ibb.co/i6ppyb

When i only increase the amount of air from the tunnel inlet i get a different picture, and there i no real connection for me to see

https://ibb.co/mJBxjG