we want to find airflow on a car inside a box. When we import the car, it doesn't go inside the box. How can we do that?
You need to subtract your car from the box to create a single flow volume of the air around the car. Make sure the box is large in the same proportions as in the tutorial "Flow Over a CO2 Dragster".
For more see the discussion "F1 in Schools Problems (Caedium Pro. Issues)".