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Old 03-28-2019, 06:52 AM   #61 (permalink)
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Originally Posted by mpg_numbers_guy View Post
Those have got to be some of the sharpest smooth wheel covers I've seen! Nice work!

Did you use fiberglass or vinyl to cover up the holes before painting?
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I had some CF/fiberglass sheet that I used. It was warped and not fit for anything else so I put it to good use.

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Old 04-07-2019, 06:07 PM   #62 (permalink)
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So done some investigating, tracing the route of the airflow after it goes through the radiator on my car. I've long suspected the exit route is out the front wheel wells; the front underfloor of the Dart is very well sealed and the swirling wheel is an enticing source of low pressure relative to the slow moving radiator exit air bumping around in the engine bay.

So the air exits the radiator (image bottom), plows into the turbo and transverse block (image center), and then out and into the low pressure area of the very inviting front wheel well (not pictured):


So you understand where we're looking, into the wheel well of the RH wheel, the leading side of the wheel well, inboard:


Amongst all this rabble is an outlet. It's not particularly well defined, but the opening (where the half shaft pokes out) is much larger than would needs be if it wasn't doing double duty. And there is further evidence that my hunch is correct (see image below):


There is a gurney on the trailing edge of the leading wheel well exit. This works to enhance the low pressure draw.


I've flirted with increasing the height of that gurney, the idea being that it draws even more air through the radiator, lowering temps, and causing the active grill shutters to be closed more often. But I suspect the gurney is already sized to achieve close to that, so I'm on the fence.

Anyhow, thought this might be enlightening to some, the airflow path of the cooling system. The cooling system produces roughly 1/3 of a car's total drag (the other being the underfloor, 1/3, and the exterior shape, also 1/3), so it's important to look at all aspects. Surprisingly the Dart's inlet side is actually pretty good, I've sealed up a few inlet-to-radiator gaps (very small gaps), but that's about all that can be done there. The let down is the exit, but there is precious little that can be done given the architecture and confined space.
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Old 04-10-2019, 10:26 AM   #63 (permalink)
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The 'gurney' flap may just be a stiffener to prevent flutter in the panel.
Since the wheel well is in accelerated flow,it will be at a lower static pressure than at the forward stagnation point ahead of the radiator.That being,the air must scavenge out through any penetration in the wheel well,simply by virtue of the pressure differential.
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Old 04-10-2019, 01:49 PM   #64 (permalink)
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Where did you buy such hubcaps?
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Old 04-10-2019, 01:52 PM   #65 (permalink)
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Where did you buy such hubcaps?
He built them from regular hubcaps. See the previous pages on this thread for reference.
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Old 04-10-2019, 05:27 PM   #66 (permalink)
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Quote:
Originally Posted by aerohead View Post
The 'gurney' flap may just be a stiffener to prevent flutter in the panel.
Since the wheel well is in accelerated flow,it will be at a lower static pressure than at the forward stagnation point ahead of the radiator.That being,the air must scavenge out through any penetration in the wheel well,simply by virtue of the pressure differential.
Stiffener, perhaps. But what if the low-pressure draw of the wheel well and the spinning wheel wasn't deemed to be enough of a draw? Would they augment that draw?
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Old 04-11-2019, 02:08 AM   #67 (permalink)
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That's the question; it takes hours in a wind tunnel to sort out.
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Old 04-13-2019, 01:57 PM   #68 (permalink)
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augment

Quote:
Originally Posted by woodstock74 View Post
Stiffener, perhaps. But what if the low-pressure draw of the wheel well and the spinning wheel wasn't deemed to be enough of a draw? Would they augment that draw?
One thing we might consider is,that on the 'windward' side of the panel,the 'bell-mouthed' rolled edge would help mitigate a vena contracta entry loss (extreme drag!),however,nowhere else in the image do we see the same care taken elsewhere in the penetration,to smooth those other pathways.
To act as a Gurney flap,the air would have to be attached to the outboard surface of the inner fender well and moving perfectly from front to rear,in order for the flap to trip the flow,creating the low pressure wake-induction.
Since some cars use wheel wells for high pressure engine air snorkel intakes,it suggests that the air inside is rather stagnant,isolated from the active airstream beyond the fender.
Complicating things more,is to follow alongside some vehicles in a rain, where you can observe spray ejecting perpendicularly from the wheelhouses.
Pininfarina will spend $100,000 of Ferrari's money just to tune very small features like this.
A Go-Pro and a smoke bomb inside the engine bay would tell us something.
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Old 04-14-2019, 11:33 AM   #69 (permalink)
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I've become obsessed with sharpened trailing edges as a means to increase turbulent kinetic energy by sudden flow separation energizing the base area. I've been contemplating sharpening the quarter panel trailing edge on the Dart as it's a large round/bulbous radius as it transitions to the bumper, I've decided on a method, but the realization is that it would be really time consuming and I'd still have to come up with a seamless method for mounting this "patch". So that got me looking elsewhere on the car. My eyes fixed on the trailing edge of the trunk:



It's decidedly thick, about 30 mm on the flat, here it is in cross section:


The trailing edge curves in 3 dimensions, complicating any fabrication. And as I'm wanting to avoid any extensive fabrication as it slows the entire process, I began to brainstorm simple solutions and landed on adhesive weather stripping. Being rubber, it will bend to the shape, it's adhesive backed, so method of mounting is solved (and I can augment with aluminum tape or helicopter tape), and there are a variety of shapes to choose from, and it's relatively cheap. Naturally I'm looking for a 90ish degree angle. However, this turned out to be harder to find than it seemed. I landed upon this shape from McMaster-Carr. Here is what it would look like in place on the hood trailing edge:


All this got me thinking. I've just recently purchase a DLP 3D printer. The beauty of the 3D printer, amongst many other things, is that there is a variety of materials to choose from. One is a rubberized urethane. So I started thinking about designing a bespoke extrusion shape. The only issue I have is that my build box is somewhat limited (155 mm in Z), and to stretch the width of the trunk (about 1300+ mm) would require multiple extrusions stitched together (about 8). So I'd be looking to design an acute angle extrusion, to draw air into the base area, and then add a bit of energy with a sudden separation (sharp TE):

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Old 04-17-2019, 11:11 AM   #70 (permalink)
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base pressure reduction

The overall base pressure is governed by the pressure which exists at the first location of of flow separation.
It may turn out that the flow along the flanks of the trunk will determine this pressure.
This is why box-cavities or boat-tails always unify the entire axial perimeter separation line.

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