A belly pan question

[Bryce]

Benjamin, I though we were talking about the quarter window ducts. Hmm. I have to give those some thought. I dont think those would work very much. They would have to do some windtunnel testing to verify flow over the back window. Usually the flow has not come back down to the window at that point. But the interior of the car is usually high pressure and the back window is lower pressure. So you would have a outward flow at that point but not due to the NACA duct specifically. If you had a laminar flow over that duct it would work.



Let me look through my areo books and see if I can find the calculations for the NACA ducts.

[The Stickman]

The reversed NACA duct would be easy enough to test. Say make a temp side window out of something with the duct mounted to it. Heck even cardboard would work. Then go for a drive and see if it pulls air, draws it in, or does nothing.

[Bjkadron]

Benjamin, I though we were talking about the quarter window ducts. Hmm. I have to give those some thought. I dont think those would work very much. They would have to do some windtunnel testing to verify flow over the back window. Usually the flow has not come back down to the window at that point. But the interior of the car is usually high pressure and the back window is lower pressure. So you would have a outward flow at that point but not due to the NACA duct specifically. If you had a laminar flow over that duct it would work.

Let me look through my areo books and see if I can find the calculations for the NACA ducts.

Nope, the side ones are correct. I was talking about the one in the picture. Every fastback I have seen has flow separation or at least increased boundary layer thickness or turbulent flow. With the spoiler there creating a high pressure area, and with the tubing going somewhere the inside/outside pressure difference would be negated I wold think.

[Bryce]

Nope, the side ones are correct. I was talking about the one in the picture. Every fastback I have seen has flow separation or at least increased boundary layer thickness or turbulent flow. With the spoiler there creating a high pressure area, and with the tubing going somewhere the inside/outside pressure difference would be negated I wold think.

I dont think that spoiler does much unless the car has vortex generators on the trailing edge of the roof.

It would need testing to verify. I would just put some pitot tubes (monometer) in that area to test for pressure. If you have a lower pressure on the outside versus the inside of the back window you could make those vents work.

I saw a studebaker streamliner that had a huge duct from under the car to right behind the rear window. I will try to find the picture.