Technical explanation of what diffusers do
#21
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Originally Posted by Borbor
Almost in all cases, all those cars are flatbottomed, or nearly so. I still can't see how a diffuser on a non flat bottomed car.
I enjoyed this sentence.
also, teh Z was designed with a pretty flat bottom. most components are tucked above the floorboard level.
#22
That's the part I don't understand There's got to be a reason why those "exotics" all have a floor to go with the diffuser.
Same case on a race car; they all have floors.
edit: editted the previous post for errrr english brainfart
Same case on a race car; they all have floors.
edit: editted the previous post for errrr english brainfart
#23
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it's just the most efficient... but it's also expensive, illogical for a road car and probably impossible to package the car with it on the cheap.
you can have a diffuser at the front and rear work independently of each other.
just like the stock diffuser (yes we have a stock front diffuser) has the concave area, that is where the downforce is created. as you all discussed already.
there will still be airflow over the rear that can be used to create downforce by a diffuser, it just will not be as optimal as perfectly straight airflow.
you can have a diffuser at the front and rear work independently of each other.
just like the stock diffuser (yes we have a stock front diffuser) has the concave area, that is where the downforce is created. as you all discussed already.
there will still be airflow over the rear that can be used to create downforce by a diffuser, it just will not be as optimal as perfectly straight airflow.
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Originally Posted by Borbor
I think one must remember something when it comes to cars kitted with diffusers (whether it's for race application, or straight from the factory)
Almost in all cases, all those cars are flatbottomed, or nearly so. I still can't see how a diffuser would work on a non flat bottomed car.
@ terrorist: Milliken as INTORDUCTORY??? LMAO.
RCVD isn't exactly a bedtime reading material; it's more of a reference when you actually have something at hand to work with and are using that book for reference.
Almost in all cases, all those cars are flatbottomed, or nearly so. I still can't see how a diffuser would work on a non flat bottomed car.
@ terrorist: Milliken as INTORDUCTORY??? LMAO.
RCVD isn't exactly a bedtime reading material; it's more of a reference when you actually have something at hand to work with and are using that book for reference.
You'll want a flat bottom and a diffuser without too steep an exit angle, otherwise seperation will occur.
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Originally Posted by Motormouth
what do they mention in that book about maximum ride height before loss of any aero benefits to lips and diffusers? Isn't it a few inches?
I would think that the splitter design on the Nismo 350Z (raised middle portion) would combat pitch sensitivity, as well as provide an inlet to the underbody.
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I didn't get too far in that book, but there wasn't too much in the aero department. But I thought you'd want the car low to the point that it isn't bottoming out or if the boundary layer started messing with the car. Not for ultimate downforce figures but to keep the car predictable at the limit.
#30
Originally Posted by Motormouth
that is not what I meant.
they say splitters, underbody trays and diffusers loose a large % of thier effect and effeciency at over a certain maximum height. I forgot what the quoted distance is.
they say splitters, underbody trays and diffusers loose a large % of thier effect and effeciency at over a certain maximum height. I forgot what the quoted distance is.
i thought it wasn't more so height (although that is important due to airflow speed) it was the angle due to flow separation.
for rear it was like the diffuser's effectiveness decreases as the angle of attack increases over 6 degrees.. (which is what the stock muffler is at)
there's supposedly this really good SAE journal/whitepaper written by a Japanese student/researcher on car aerodynamics and their work, but i could never find it.. i tried poking around teh interwebs ,but never found out. i think i was on http://www.eng-tips.com/ when i first heard about it.
#31
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God I love it when I stumble onto these super informitive threads, you guys are answering every question that I've been searching for. Reminds me of the RX-7 forums! Keep it up.
On a side note, Chebosto what diffusor set up are you running, front/rear/side/wing? IIRC you track test and alter your set up frequently.
On a side note, Chebosto what diffusor set up are you running, front/rear/side/wing? IIRC you track test and alter your set up frequently.
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Ride height shouldn't really affect splitter effectiveness; after all, a splitter only relies on stagnant pressure across where it is attached to. As a means of providing an underbody inlet, again height would be adjusted according to meeting regulations, and making sure that the underbody isn't choking.
As for angle of attack for the diffuser (alpha), usually you would want to keep it small such that the flow doesn't detach.
http://www.mulsannescorner.com/techarticle1.htm
http://www.mulsannescorner.com/benzCLR1.html
These articles are interesting...
As for angle of attack for the diffuser (alpha), usually you would want to keep it small such that the flow doesn't detach.
http://www.mulsannescorner.com/techarticle1.htm
http://www.mulsannescorner.com/benzCLR1.html
These articles are interesting...
Last edited by terrorist22; 12-04-2007 at 08:45 PM.
#34
there is a really interesting picture in the 6th issue of the japanese Z magazine. (i got mine off Amazon.co.jp)
there was a CFD model of the new Nismo edition Z; color coded for high (red) and low (blue) pressure zones. they actually had a shot of the underside of the car.
in the stock form, there was naturally high pressure right at the front tire, but deep(er) blue zones immediately following the end of the front undertray (which acts as a front diffuser) and a deep blue zone immediately following the stock exhaust. what i thought was interesting was that there were blue zones (although not as dark) where the front underside framing/catalyst converters sat, and turning green (slightly higher pressure) right before the rear sub frame. true this car isnt completly flat underbody like a ferrari, but it's pretty good, and i do think you would be able to feel the effects of underbody enhancements at high speeds. that nismo kit really looks good on a design standpoint.
i'll try to scan that image when i get home...
there was a CFD model of the new Nismo edition Z; color coded for high (red) and low (blue) pressure zones. they actually had a shot of the underside of the car.
in the stock form, there was naturally high pressure right at the front tire, but deep(er) blue zones immediately following the end of the front undertray (which acts as a front diffuser) and a deep blue zone immediately following the stock exhaust. what i thought was interesting was that there were blue zones (although not as dark) where the front underside framing/catalyst converters sat, and turning green (slightly higher pressure) right before the rear sub frame. true this car isnt completly flat underbody like a ferrari, but it's pretty good, and i do think you would be able to feel the effects of underbody enhancements at high speeds. that nismo kit really looks good on a design standpoint.
i'll try to scan that image when i get home...
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so if you have a diffuser, would "speed holes" still have any benefit in realeasing any pressure from some of the air that gets stuck between the diffuser and the underside of the car? or would speed holes disturb the air flow from the diffusers?
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Originally Posted by creationv2
so if you have a diffuser, would "speed holes" still have any benefit in realeasing any pressure from some of the air that gets stuck between the diffuser and the underside of the car? or would speed holes disturb the air flow from the diffusers?
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here is a cool article: http://www.clarkson.edu/honors/resea...an-Michael.doc
there is a term called 'critical ride height', that I see people referencing about aero efficiency at ride heights. Just like you can be too low from the CRH, when you increase the ride height over the CRH it does the same, and lowers the effect the undertrays have on the downforce produced.
there is a term called 'critical ride height', that I see people referencing about aero efficiency at ride heights. Just like you can be too low from the CRH, when you increase the ride height over the CRH it does the same, and lowers the effect the undertrays have on the downforce produced.
Last edited by Banndmanback; 12-10-2007 at 10:37 AM.
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too much air flowing under the car is undesirable. i.e. increase ride height or increased pitch angle of the leading edge. I am only considering static arguments and not related to suspension compression or squash.
Really, there is a large wealth of information on how ride height is a hugely important part of the downforce equation. They say that aero trays on most road cars are wholly ineffective because our static ride heights are far to tall. on a car like Chestons, which is basically a race car ride height from the pictures on this site!, they will be very effective.
how high do you think the average Z's front bumper is off the ground? 35mm? 50mm?
Really, there is a large wealth of information on how ride height is a hugely important part of the downforce equation. They say that aero trays on most road cars are wholly ineffective because our static ride heights are far to tall. on a car like Chestons, which is basically a race car ride height from the pictures on this site!, they will be very effective.
how high do you think the average Z's front bumper is off the ground? 35mm? 50mm?
Last edited by Banndmanback; 12-10-2007 at 11:04 AM.