Sorry for the incomplete case set up. I tried many times but it failed.
The simulation is basically external aerodynamics for the diffuser ( undertray ).
It works in close proximity with the ground to develop low pressure underneath race car and generates downforce.
I approached the problem by employing symmetry. The bounding box details are
The body along with the floor (Zmin ) is to be inflated. The geometry is at designed ground clearance of 63 mm (Zmin=0)
I hope this helps with the simulation setup.