Interface Contact Region
 

Hai everyone, I am currently performing the CFD simulation on air pollution. But, although I have finished the simulation, the result is not good. So, I have referred to some other tutorials on this related topic, and I think there is something wrong with my geometry because there is a layer called contact region, in which I cannot set it as "wall". I think this is why the simulation yields an inaccurate result. Does anyone know about this?

Many thanks.