I am trying to do a CFD model of a simple car. More specifically, I am looking at the effects of an under-body diffuser. I am trying to figure out how to setup the model in Flow Simulation. I've set up an external flow situation, the main thing I'm trying to figure out is how to make the ground beneath the car. Right now its giving me results similar to the car being suspended in mid air. I'm also wondering, if it's possible to simulate a moving road.

Thanks for your help.

Peter