Originally Posted by FDNewbie
(Post 7678115)
...that's a lot of assumptions. BUT:
1) To assume they ARE far back enough is an assumption in it of itself...
Originally Posted by FDNewbie
(Post 7678115)
...You'd be catching either a high pressure area, equalized pressure area, or the very beginning of a low pressure area (def. not as good as say, the much more forwardly located side vents on the Mazdaspeed R-Spec hood).
Originally Posted by FDNewbie
(Post 7678115)
Re: the negative pressure, assuming the oil ducts are vented openly to the wheel well, and you have a normally shaped fender (not concave); would there be sufficient enough negative pressure generated to vent the air in the wheel well out of the fender vent (that's normally used for the oil cooler vent)? Assuming you enlarged the vent too... Or would that be not such a good idea, and going w/ the concave fenders is the way to go? Not sure if the former would involve too much turbulence/inadequate vent size, etc.
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Originally Posted by Kento
(Post 7678278)
The difference is that I've given some facts and knowledge to back up my assessment of your assumption.
Note that I stated I never was saying outright that the RE Amemiya vent was effective. BUT: The underhood area is in itself a higher pressure area than most of the area above the hood, because pressure is being built up from the front intake. Thus, if it was an area of equal pressure or below, you'd still get benefits from the vent.
Originally Posted by NZConvertible
(Post 7666840)
I know you're just making numbers up for the sake of discussion, but I don't think many people appreciate the magnitude of the pressures we're discussing here.
The static pressures measured across the top of the hood would be in the order of a few hundred pascal's, compared to atmospheric pressure of 101,325Pa at sea level. So a measured static pressure of 250Pa (which is realistic) is only ~0.25% of atmospheric pressure. Dynamic pressure at 100mph is ~1200Pa, which is a lot higher than the static pressure but still only a small fraction of atmospheric pressure (~1.2%). A wheel well by itself doesn't generate that much negative pressure, so any vent that can help evacuate air from the wheel well can't hurt in that case. The concaved fender generates a lot of turbulence as well as neg pressure, so it can go either way depending on other factors. |
Originally Posted by FDNewbie
(Post 7678319)
So from THAT, I understood that it would take an *enormous* amount of pressure buildup in the engine bay to vent through the high pressure zone in the rear.
Originally Posted by FDNewbie
(Post 7678319)
But hopefully the fact that it isn't positive pressure is enough to improve airflow through the oil coolers...
Originally Posted by FDNewbie
(Post 7678319)
I wondered about that as well...the tradeoff between negative pressure & turbulence, as I've seen how many of the land speed cars (including the RacingBeat FD) cover the wheel wells due to the tremendous turbulence they noted from that area (and if I'm not mistaken, many of the smaller hybrid vehicles also partially cover the rear wheel wells for the same reason, because less turbulence results in better gas efficiency, yes?)
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Originally Posted by Kento
(Post 7678374)
Sorry Ramy, but you understood incorrectly. "Dynamic pressure" occurs on surfaces that are directly facing the airflow, so the "enormous" ~1200pa reading isn't at the windshield junction. And definitely not at the area we're speaking of.
You're talking about the difference between direct airflow from the oil coolers versus a slight negative pressure area in the wheel wells. Less turbulence means less aerodynamic drag, the main goal of land speed vehicles. Thanks again :) ~Ramy |
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