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Old 02-24-2019, 06:38 PM   #2964 (permalink)
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Car Design History, Concept cars, Automotive advertising, auto designers and design studios in general is a goldmine.

Reposting from this other thread:

I was searching for something else and I found a thread from 2016 where a forum member, stealth, applied CFD modeling to the question. Here's the result:

On the model that has 100mm of ground clearance, flat base, removing the inverted horn increased the drag from 5.4N to 5.9N, increase of almost 10%. The pictures shows that without the airflow that going through the horn and pushing up the wake, it allows the airflow from the top go down and push aside all of the other airflow.
However what's interesting is that for the 30mm ground clearance, the drag values are near identical. I think this is because of the size of the horn and the low ground clearance makes for a rapid expansion of the airflow which has similar drag level to having a solid back end.
It all depends on the size of the horn and the ground clearance but I think it can be used to reduce the drag if done correctly. In terms of the Cd accuracy, in terms of real world predictions, the software wouldn't be any good unless I can get some real world validation, but it's accurate and consistent for when comparing designs and their drag values.
My interpretation is that the second picture has the flat transom and the third has the bell. It appears to add order to the lower part of the wake. And with +70mm of air moving, 10% less drag.
I'm a fan of the exponential bell diffuser.
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