NASCAR technical question

[Knestis]

...Mechanical engineers only use Bernoulli as a very rough first assumption, but often embedded are much better solvers with different forms of Navier-Stokes simplifyed, as it's a non-linear differential equation. ...[/b]

But that approach completely neglects the Areola-Spanakopita index of turgidity, well recognized as having an deleterious influence on the magnanimity of non-linear Navier-Stokes salutations. The only proxy-delamination opticient to the pentile clarendon, is the twixt-inductee caroming fork of the manic prong method. We see this appendication in prescient turd-swirlers - but you knew that. (See Nottybitz, 2004)

K

[Black91n/aRX-7]

Ok, this week's assignment is to read all of the articles found here:

http://www.advantage-cfd.co.uk/Newsletter/...r-Articles.html

You can thank me later

[Racefreak24]

Well keeping to the AERO topic, and since I have such a knowledgeable group here can someone explain undertrays and other under car aero and it's effects. Is this equipmant you can buy or is it individual car adjustments such as muffler, brake pads. I know open wheel have an extensive underbody aero system.

[JeffYoung]

And the corollary to Kirk's post:

Beavis say: "The angle in the dangle is inversely proportional to the heat in the meat."

So there.

[Z3_GoCar]

.... We see this appendication in prescient turd-swirlers - but you knew that. (See Nottybitz, 2004)

K
[/b]

What is that like a temporally displaced toillet?? Kirk, I'm calling B.S. on that :P

Well keeping to the AERO topic, and since I have such a knowledgeable group here can someone explain undertrays and other under car aero and it's effects. Is this equipmant you can buy or is it individual car adjustments such as muffler, brake pads. I know open wheel have an extensive underbody aero system.
[/b]

An undertray is one large cover that keeps all the moving drag inducing elements out of the air flow on the bottom. Some of the first users of undertrays were the dry lakes racers. They'd reached the point that all the little details on top were taken care of, and were looking for places to cut drag even more. A later incarnation of the undertray used the channeled air flow to increase down-force, or at least to locate a low pressure zone so that the race-car is properly balanced. The problem with depending on an under-tray for down force is that one little bump and all of a sudden the down force you were depending on goes away. Also, with production based cars, that's a rather large area to cover, and it's often not allowed to cover it anyway per the rules. Formula cars can get away with an undertray as there's not much down there, or the rules alow it. My friends FC Van Deimon has a nice little carbon tray under the power plant that opens up into a diffuser. He's running VARA since there's no place for his car in SCCA anymore

[lateapex911]

The IT ruleset kinda prohibits aero devices with the exception of airdams and factory equipped spoilers.



However, the airdam is free essentially, and as long as it fits within the prescribed limits, all is good. Splitters can be incorporated, and undertrays could be integral as well, but they need to terminate where prescribed by the airdam rule limit.



Some creative types might weld a large flat plate covering much of the underside to the muffler, and call it part of the exhaust system, which is free. That would result in some chuckles, some rolled eyes, and maybe a protest based on the "No device can perform a prohibited function".



Might make it by the stewards, might not...

[Greg Amy]

Sometime in the last year or so there was a topic on airdam spoilers and splitters. Started by Bettencourt, as I recall. In it I uploaded a PDF of Race Car Engineering articles on that very topic of spoiler, splitters, and undertrays. Use the search function and see fi you can find it...

[ddewhurst]

***But that approach completely neglects the Areola-Spanakopita index of turgidity, well recognized as having an deleterious influence on the magnanimity of non-linear Navier-Stokes salutations. The only proxy-delamination opticient to the pentile clarendon, is the twixt-inductee caroming fork of the manic prong method. We see this appendication in prescient turd-swirlers - but you knew that. (See Nottybitz, 2004)***

Forget this ^ BS, it's not approved Man Law.

[evanwebb]

Just to throw in my $.02, (trying to remember my fluid dynamics from grad school...) I think that it is the case that airflow over real cars isn't laminar past the top of the windshield, if it gets that far. At that point (I think Greg? alluded to this mentioning the vortex generators on EVOs or WRXs or something?) the flow can either become turbulent or separated. These are two rather different states, and turbulent airflow is still considered "attached" and is much less draggy than separated flow. Vortex generators actually create turbulent flow by adding energy to the airstream. The combination of how much energy is required to create turbulent flow vs separate the flow, and how much bodywork is in contact with the turbulent or separated flow, results in how much drag is created. Reducing the amount of bodywork in contact with these flows reduces the amount of drag on the car, and the short chopped-off tail of the cars known as Kamm tails use this strategy (see the Cobra Daytona coupes of Peter Brock for example). Also, this is why golf balls are dimpled rather than round, the airflow over "real" surfaces in the real world doesn't stay laminar very long, and then it goes through a very quick transition to turbulent and then separated flow. The dimples actually act to cause the flow over the entire golf ball to be turbulent for as long as possible before transitioning to separated flow, hence the ball is less draggy and you can hit it further. Unless you are me, in which case you mostly don't hit it at all, or you hit a "worm burner" along the ground...

Just to throw in my $.02, (trying to remember my fluid dynamics from grad school...) I think that it is the case that airflow over real cars isn't laminar past the top of the windshield, if it gets that far. At that point (I think Greg? alluded to this mentioning the vortex generators on EVOs or WRXs or something?) the flow can either become turbulent or separated. These are two rather different states, and turbulent airflow is still considered "attached" and is much less draggy than separated flow. Vortex generators actually create turbulent flow by adding energy to the airstream. The combination of how much energy is required to create turbulent flow vs separate the flow, and how much bodywork is in contact with the turbulent or separated flow, results in how much drag is created. Reducing the amount of bodywork in contact with these flows reduces the amount of drag on the car, and the short chopped-off tail of the cars known as Kamm tails use this strategy (see the Cobra Daytona coupes of Peter Brock for example). Also, this is why golf balls are dimpled rather than round, the airflow over "real" surfaces in the real world doesn't stay laminar very long, and then it goes through a very quick transition to turbulent and then separated flow. The dimples actually act to cause the flow over the entire golf ball to be turbulent for as long as possible before transitioning to separated flow, hence the ball is less draggy and you can hit it further. Unless you are me, in which case you mostly don't hit it at all, or you hit a "worm burner" along the ground...

[nswanberg]

Any of you computational fluid dynamics experts ever seen any of the studies dealing with random surface imperfections and reduced drag on water vessels? I have wondered if there might be any high speed automotive applications. Only problem is our cars would not look all shinny and pretty.

NS

[lateapex911]

..... Only problem is our cars would not look all shinny and pretty.

NS
[/b]

I guess you've never been to an SCCA Prod car grid!

Kidding, kidding..

(just a little rejoinder to the Prod car guys who criticise IT for being a category of junkers... )

[Eagle7]

... Also, this is why golf balls are dimpled rather than round, the airflow over "real" surfaces in the real world doesn't stay laminar very long, and then it goes through a very quick transition to turbulent and then separated flow. The dimples actually act to cause the flow over the entire golf ball to be turbulent for as long as possible before transitioning to separated flow, hence the ball is less draggy and you can hit it further....
[/b]

So my orange peel paint job makes me faster! Cool.

[Dyno]

So my orange peel paint job makes me faster! Cool.
[/b]

My college fluid mechanics book had two interesting photos... The first was a side view of a bowling ball dropped into a glass tank of water from some unspecified height. The second photo was that same bowling ball dropped into the same tank after it had it's leading hemisphere coated with glued-on sand.

The wake created by the sand-coated ball was much smaller than that created by the smooth ball.

Orange peel is good!

[ddewhurst]

A gillion years ago Petty Enterprises put a layer on their race car roofs similar to the surface of a golf ball.

[Dyno]

A gillion years ago Petty Enterprises put a layer on their race car roofs similar to the surface of a golf ball.
[/b]

New product idea: Produce a helmet that looks like a golf ball. Sell to formula guys. Wouldn't they look cool?

[lateapex911]

Yea! AND whats cooler would be all the Callaway Big Bertha marks from confused duffers all over the helmet!

[Conover]

If you look underneath a lot of New cars you'll see dimples all over the bottom. The most recent one that I've seen is the MKV Jetta. Apparently they've got the airflow under that car figured out pretty well, because there is an automatic transmission cooler mounted horizontally level with the rest of the underside of the car.

And I didn't see any Turd Swirlers anywhere near there.

[sstecker]

If you look underneath a lot of New cars you'll see dimples all over the bottom. The most recent one that I've seen is the MKV Jetta. Apparently they've got the airflow under that car figured out pretty well, because there is an automatic transmission cooler mounted horizontally level with the rest of the underside of the car.

And I didn't see any Turd Swirlers anywhere near there.
[/b]

a bodyboard manufacturer came out with boards years ago with a dimpled bottom surface.

[Racefreak24]

OK here we go again.....why does nascar have the roof spoiler at Daytona and talladega...I know it slowes them down and keeps them in a bunch but what aero effects does it have? And also they have a vertical fin down the drivers side of the rear window at these tracks as well. Any input?

[lateapex911]

As far as I recall, the roof dam is all about drag and slowing the cars down.

The longitudinal fins on the rear window are part of the 'spin and lift abatement program'. I seem to remember they came into effect when all the cars started floating up when they got sideways to the wind, and that fin spoils the airflow and kills the lifting effect. The roof flaps that pop open when the roof sees the low pressure during a spin are there to create the same result.