Quote:
Originally Posted by Big time
Roof camber data seems to show that while Cd decreases with higher roof camber, overall CdA goes up as the increase in frontal area won't compensate for the lower Cd.
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You might want to do a search in this forum, look for the tread when a similar topic came up regarding semi-truck tractor trailers.
The prevailing argument was that the lowest possible frontal area (flat roof) would be preferred over a larger and taller trailer with aerodynamic roof hump (tear-drop).
However, I did find many links from the UK which argued otherwise. They were in all fairness from companies making aerodynamically shaped truck trailers. Most were smaller in overall volume and load capacity than the ones we are more familiar with here in the USA, which accounted for even more striking differences.
What you see here in this thread is an agreement that the devil is in the details, and a carpet coverall conclusion best not be made.
There are just too many other factors which could easily change any general assumption. For instances as mentioned the transitional arc over the top of the windshield and so forth which may affect actual air flow.
EDIT: Page 8 of the link you provided touches on your question when it mentions the suction of a flat roof due to loss of boundary layer adhesion.
In This Chapter the Modifications That Were Carried Out To
In this context or example I would have to agree with the author of that book. The bubble roof or roof arc is better in the case illustrated, and for the reasons they state.