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Old 09-18-2020, 04:35 PM   #3561 (permalink)
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Originally Posted by freebeard View Post
This seems weak. What is the mechanism by which the imaginary shape acts [through an impenetrable surface]/[in meat space]?
'[T]he optimum shape in terms of drag is a half-body, which forms a complete body of revolution together with its mirror image- produced through reflection from the roadway.' Wolf Heinrich Hucho, page 15, Aerodynamics of Road Vehicles, 2nd-Edition,Butterworths, 1986.
This has to do with 'effective fineness ratio', a phenomena of aerodynamics, in which a vehicle is twice as 'thick' as what you observe.
In order to achieve the drag minimum of a Length / Diameter of 2.5: 1 streamline body, the car must be 5:1. The template.
A look at early wind tunnel testing reveals models humping, wheels -to-wheels in the air stream to accommodate this phenomena.
I don't have the book with me so I can't go any deeper.

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