This is a picture of CFD analysis for the Chevy Volt.
The article went on to say that nowadays, the preferred method of measuring air drag is with CFD.
Building a clay model with the same level of detail that can be achieved with the CFD is cost prohibitive, and the CFD gives the results in a reasonable time period.
The grill was detailed in such a way as to meet the cooling requirements on the hottest day in Arizona for example.
Jim.