Quote:
Originally Posted by freebeard
I'm not sure what you're saying here. Holes to the upstream exterior, or to the interior?
Open box-cavities OK?
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The base pressure of the entire wake is determined by pressure existing at the line of separation nearest the lowest pressure point on the body.Typically just ahead of the windshield/A-Pillars.
If a box cavity isn't airtight around it's attachment point interface and periphery,the base pressure of the wake behind it will be governed by the pressure of the separation line ahead of the trailing edge where any 'hole' exists,telegraphing this low pressure into the rest of the wake.So it is an upstream exterior effect.
This is why air will flow backwards from an open hatchback,bringing exhaust fumes into the cabin when a front window is rolled down,rather than channel air rearwards into the wake.It's all about pressure equalization.