Thanks..........Skip Reber
Louvers and open side pods
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Skip Reber |
Louvers and open side pods |
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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 | |||
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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 | |||
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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 | ||
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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.
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Skip Reber |
#4 | |||
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Thanks guys. It's always good, and never too late, to get educated.
Skip |
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Duane Dyckman |
High Pressure | #5 | ||
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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 | |||
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You're right , Duane - I was just testing the readers to see who would find the flaw in my analysis...
Clark |
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Speedquest |
Louvers and Open SidePods | #7 | ||
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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 | |||
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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?
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Skip Reber |
#9 | |||
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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 | |||
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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 | ||
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Clark
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Duane Dyckman |
#12 | |||
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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 | |||
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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 | |||
Duane Dyckman wrote: Duane,
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Duane Dyckman |
#15 | |||
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Thanks Rennie. I thought the aero gurus were a little too silent on this. Appreciate the info.
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Skip Reber |
#16 | |||
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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 | ||
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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 | |||
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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 | ||
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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 | |||
ted james wrote: 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.
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