Louvers and open side pods

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Skip Reber	Louvers and open side pods		Lead	[-]
Registered User Posts: 141 03/17/08 16:14:42	Tags : None I notice that most, if not all, current sports racers feature both open side pods and louvers on the tops of the front fenders. To my naive way of thinking, the open side pods should be sufficient to relieve the air pressure behind the front wheels, and that the louvers are an unnecessary addition that just complicate the fabrication of the front body section. I would also think that louvers, by themselves, would not suffice. What am I missing? Thanks..........Skip Reber
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Marty Nygard		#1	[url]	[-]
Registered User Posts: 198 03/17/08 17:04:59	The shape of the top of the front fenders can act to generate lift. Louvers exhausting into this area can cancel the lift. Marty
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Clark Lincoln		#2	[url]	[-]
Registered User Posts: 707 03/17/08 21:36:27	and the highest pressure generated by a rotating tire is above and just behind the top of the tire - therefore the location of most louver panels. The open side pods are primarily to exhaust air from under the front undertray/splitter. If you notice LMP cars use minimum louvers at Le Mans (high speed required track) and massive quantities of louvers at shorter and slower tracks that demand high downforce - like Mid Ohio. They are a *%+%% to make and get broken often (crap flying off the tire), but are very important. Clark
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preformresources	lmp louvers	#3	[url]	[-]
Registered User Posts: 543 03/18/08 08:45:49	A good example of what Clark is pointing out, check the new Lola coupe on Mulsannes corner,the footprint of the louver panel is much greater than the louvered area and in the rear there seems to be a removable panel also potentially for louver placement. Dave Craddock http://www.mulsannescorner.com/newsmarch08.html
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Skip Reber		#4	[url]	[-]
Registered User Posts: 142 03/20/08 13:48:03	Thanks guys. It's always good, and never too late, to get educated. Skip
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Duane Dyckman	High Pressure	#5	[url]	[-]
Registered User Posts: 275 03/21/08 13:52:12	Clark, Reading Joseph Katz, I don't think he agrees that the highest pressure is above and just behind the top of the tire. Fig 6-24 on page 196 shows the highest pressure, of a rotating wheel, as just AHEAD of the top of the tire. If you examine the photographs from the early 90's and present, both show the louvers well ahead of the top of the tire.
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Clark Lincoln		#6	[url]	[-]
Registered User Posts: 711 03/21/08 14:30:46	You're right , Duane - I was just testing the readers to see who would find the flaw in my analysis... However, in as much as our louvers can't expose the tire from above, it's easiest to locate them just aft of the top of the tire - and be really careful how you trim out the slots. Clark
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Speedquest	Louvers and Open SidePods	#7	[url]	[-]
Registered User Posts: 32 03/24/08 08:41:27	The air from the front undertray is directed toward the radiator inlets. The open sidepods allow air from the top to be directed into the radiator inlets also, but this air is at a cooler temperture than the air from underneath, due to the temperature gradient caused by the hot, sunbaked asphalt track. As you know, tornados are caused by hot and cold air coming together, this same turbulent inlet air improves cooling. Darnel
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Clark Lincoln		#8	[url]	[-]
Registered User Posts: 712 03/24/08 13:22:54	Hey Darnel - good to see you back on the site. You make an interesting point that I am unaware of. Are these "tornados" vertical or horizontal -as I would suspect? Oh, and do they occur only in Kansas? Clark
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Skip Reber		#9	[url]	[-]
Registered User Posts: 143 03/26/08 14:17:59	Not to muddy things, but Figure 6-24 in Katz' book refers to the pressure distribution around an open wheel, not an enclosed wheel. His Figure 6-25 shows a fendered wheel, but only the direction of airflow induced by the rotating wheel, not the pressure distribution. I suspect the pressure distribution shown for the open wheel would be quite different in a fendered configuration. Skip
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Clark Lincoln		#10	[url]	[-]
Registered User Posts: 716 03/26/08 21:45:01	Skip, you're correct on the Katz reference, and I can't find my reference on the enclosed/fendered tire. I do remember seeing it - which is good for an old fart - but can't remember where... Anyway, I think why we see louvers all over the tops of LMP type cars' front fenders is a combination of venting pressure generated by the spinning tire, and reducing lift created by air passing over these curved surfaces. And they ALL use them. When we get our new car on track, we will collect downforce data on this issue and report our results. Clark
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matt1racer	Louvers	#11	[url]	[-]
Registered User Posts: 13 03/27/08 08:56:33	Clark I would be very intersted to see what you find out and what your configuration looks like. I posted a picture of mine in my photo's although i dont have any instrumentation for real data. cheers matt
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Duane Dyckman		#12	[url]	[-]
Registered User Posts: 278 03/27/08 10:19:23	Skip, Why suspect it would be quite differeent? Do you take into account the airflow over the open tire that is not present with an enclosed tire at least to the same degree? I suspect that the higher pressure moves further forward for that reason. If it did not, why are the louvers put so far forward on the fender? Well forward from the top of the tire?
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Skip Reber		#13	[url]	[-]
Registered User Posts: 145 04/02/08 12:20:30	Duane..............My thought is that the inner fender adjacent to the tire has an attached boundary layer that is (by definition) not moving relative to the airflow generated by the rotating tire (which may in turn be influenced by the airflow produced by the car's forward speed). This boundary layer, interacting with the boundary layer attached to the rotating tire, creates a three dimensional shear force between the tire and inner fender that is very sensitive to the separation of the two, and also to the shape of the fender opening as seen in side view. This shear would produce velocity and pressure distributions different from those generated by an open tire rotating in free air; how much different would depend on the specific geometry of the tire-fender combination, and on how much air flow enters at the front of the body. Of course, all this theoretical conjecture does not help at all with deciding where to install any louvers. (I guess, to cover all bases, one could have louvers running from the front of the fender all the way to the back. :-)) Skip
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Ren		#14	[url]	[-]
Registered User Posts: 517 04/02/08 14:54:59	Duane Dyckman wrote: Skip, Why suspect it would be quite differeent? Do you take into account the airflow over the open tire that is not present with an enclosed tire at least to the same degree? I suspect that the higher pressure moves further forward for that reason. If it did not, why are the louvers put so far forward on the fender? Well forward from the top of the tire? Duane, The louvres are placed that far forward because of the airflow characteristics over the fender, mostly unrelated to airflow inside the fender. The examples being cited here may be a bit extreme, but depending on the shape of the fender, the point of lowest pressure over the surface may be somewhat forward of the peak of the fender. Louvres are most effective when they can act to "suck" out air from the wheel well, rather than acting as a simple vent for high pressure turbulent air to escape. Cheers, Rennie
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Duane Dyckman		#15	[url]	[-]
Registered User Posts: 282 04/02/08 15:19:47	Thanks Rennie. I thought the aero gurus were a little too silent on this. Appreciate the info.
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Skip Reber		#16	[url]	[-]
Registered User Posts: 146 04/02/08 15:26:42	Thanks, Rennie. Actually my reply was to some earlier comments about airflow and air pressure distribution of a fendered tire compared to an open wheel tire, referencing Katz' book. As I tried to say in my long winded dissertation, I wouldn't have a clue how the inner fender air flow affects the optimum placement of louvers. Skip
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Stu Waterman	a source for louvers?	#17	[url]	[-]
Registered User Posts: 4 04/02/08 15:34:27	Has anyone found a source for ready-made louvers that are sufficiently flexible to conform to a fender? Our bodywork is flat across the top of the wheel arch, so I'm just looking for modest flexibility in the "long" dimension (parallel to the centerline of the car). Stu
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fastercar		#18	[url]	[-]
Registered User Posts: 122 04/02/08 16:08:05	I've gotten some from Ben Beasley. I think Mike Devins at HRP may be able to help and I believe I've seen them in the Heorr catalog. Good luck, Dave.....
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ted james	aero	#19	[url]	[-]
Registered User Posts: 411 04/03/08 11:06:14	my 2 cents, they are more trouble than they are worth below 150MPH. Twice we have done back to back on two different cars and could find very little if any difference. One was an AMAC the other was a WF-1.
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Ren		#20	[url]	[-]
Registered User Posts: 518 04/03/08 13:19:42	ted james wrote: my 2 cents, they are more trouble than they are worth below 150MPH. Twice we have done back to back on two different cars and could find very little if any difference. One was an AMAC the other was a WF-1. This is consistent with our experience as well on our Dauntless CSR project we took to the Runoffs last year. We had strange lift issues on the front fenders, and we went about fixing the problem in a different way entirely, by venting the area between the nose and fenders. Cheers, Rennie
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