Quote:
Originally Posted by 93tracerwagon
I am not sure exactly what these are. Is this the cavity created by recessing the rear of the vehicle like has been recommended for car mirrors and like the hatch glass of the Original VW Rabbit (about a 9% savings in drag IIRC)?
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Here is an example of a proper box cavity.
If properly inset,and of proper length,they will capture an optimized vortex,of which the inviscid flow will skip over,briefly reattach onto the trailing edge before separation.
As the flow diverges,it decelerates,gains pressure,imparting a higher base pressure,reducing pressure drag.
From Hucho's published drag tables,the maximum drag reduction is 7.9% at a length equal to 42% of the body length.(His example was a Volkswagen Transporter)