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I maintain my assertion that there is nothing special about the grille from the PopSci article. Any internal cooling flow passage that presents some net flow resistance will result in an increasingly greater portion of the external flow going outside rather than inside the passage as the vehicle speed increases. Although, the capture streamtube for the cooling passage gets increasingly narrow with vehicle speed, the volume of flow through the cooling passage still increases because the pressure difference between the inlet and outlet increases with vehicle speed. (The above discussion is a slight simplification: it is actually the ratio of external and internal velocities that determines the pressure loss coefficient and the streamtube shape.)
I researched automotive cooling airflows from 1988 to 1990 and co-wrote an SAE paper on my findings. If there actually were some amazing aerodynamic trick with a front grille, Jack Williams, my co-author from Ford, surely would have been aware of it. Jack Williams now teaches short courses for SAE on vehicle cooling aerodynamics. Anyone who wants to learn the state-of-the-art for vehicle cooling performance and drag should go to sae.org and buy a couple of Jack’s latest papers. 2001-01-0996 “Aerodynamic Drag of Engine-Cooling Airflow with External Interference” and 2002-01-0256 “Cooling Inlet Aerodynamic Performance and System Resistance”.
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