Author Topic: aerodynamics ground plain/ bottom of front air dam questions ( I think )  (Read 4686 times)

0 Members and 1 Guest are viewing this topic.

Offline Breck

  • Jr. Member
  • **
  • Posts: 32
Hey
 
Is there a substantial decrease in air pressure from the bottom of a front airdam/spoiler where it meets the ground plain, to the top of the air dam?  Common since says there would be, but .. "aerodynamics is not intuitive". 

More to the point, how much is to be gain with a lift neutral tunnel under the car, leaving the air next to the ground, right where it is?  Is there a sweet spot of height above the ground?


 Maybe like a 962 Porsche with a 6" or 12" tunnel under it, wheel enclosed in side and out.
http://www.porsche.com/usa/eventsandracing/motorsport/racingcars/962/

Would there be more drag from turbulence under the car than gained from the decreased frontal area next to the ground plain?

Just writing this I'm thinking I don't even know enough to ask the right question.  Any recommended reading ie Aerodynamics for Dummy's or something

Breck

Offline WOODY@DDLLC

  • Hero Member
  • *****
  • Posts: 1803
  • ECTA made it to AR-Kansas!
    • Design Dreams, LLC
Just depends ........ :-o
All models are wrong, but some are useful! G.E. Box (1967) www.designdreams.biz

Offline Breck

  • Jr. Member
  • **
  • Posts: 32
Hey Woody

This is interesting.  Red is high pressure, dark blue is low pressure right?  That looks like a lot of low pressure on the roof.  Positive lift seems undesirable in any form.  Couldn't they duct some of the high pressure from the base of the windshield, up the door pillars and out through a slot at the front of the roof?

Or do red and blue indicate high and low turbulence?

Breck
« Last Edit: March 06, 2011, 07:12:58 PM by Breck »

Offline WOODY@DDLLC

  • Hero Member
  • *****
  • Posts: 1803
  • ECTA made it to AR-Kansas!
    • Design Dreams, LLC
Hey Woody

This is interesting.  Red is high pressure, dark blue is low pressure right?  Correct! That looks like a lot of low pressure on the roof. Correct again! Positive lift seems undesirable in any form. You are three for three, Breck! Couldn't they duct some of the high pressure from the base of the windshield, up the door pillars and out through a slot at the front of the roof? A duct is a scoop and it has drag and internal losses! The engine usually draws from the windshield base. The "trick" is balancing all the "colors" by modifying the shapes which bent the air in the first place!

Or do red and blue indicate high and low turbulence?

Breck

Take a look at these: http://www.landracing.com/forum/index.php/topic,5612.195.html

Breck, start here: Aerodynamics For Racing and Performance Cars Hp1267 by Forbes Aird ($45~50)

A little hard to find but well worth it!   :cheers:

For more info and math:    :-D

Race Car Aerodynamics: Designing for Speed (Engineering and Performance) by Joseph Katz ($20~25)

or

Competition Car Aerodynamics: A Practical Handbook by Simon McBeath ($30)

For even more info and even more math:   :-o

Aerodynamics of Road Vehicles: From Fluid Mechanics to Vehicle Engineering ([Proceedings] / SAE) [Hardcover]
Wolf-Heinrich Hucho (Editor) ($100)

All available at Amazon.

Some other pix at my web site: www dot designdreams dot biz
All models are wrong, but some are useful! G.E. Box (1967) www.designdreams.biz

Offline Dr Goggles

  • Hero Member
  • *****
  • Posts: 3120
  • The Jarman-Stewart "Spirit of Sunshine" Bellytank
    • "Australian Bellytank" , http://thespiritofsunshine.blogspot.com/
Ah hah, I beat Rex to it....

there is another book, but it needs to be treated with caution.

Goro Tamai: The Leading Edge.

Do not operate heavy machinery or motor vehicles after reading this book and if you are currently on ANY medication consult your doctor before consuming .....

It is principally aimed at low speed hyper efficient shapes but there a lot to chew on in there.


OK, for what it's worth of the already suggested I have found McBeath the most digestable......but it's a name that is , well, unmentionable*

















* at least in theatrical circles..... :cheers:


Few understand what I'm trying to do but they vastly outnumber those who understand why...................

http://thespiritofsunshine.blogspot.com/

Current Australian E/GL record holder at 215.041mph

THE LUCKIEST MAN IN SLOW BUSINESS.

Offline Breck

  • Jr. Member
  • **
  • Posts: 32
Mornin Woody G'day Dr.Googles.. Everybody

First, Thank You Very much for the references.  It really helps to know which piles of info to jump into.

"Take a look at these: http://www.landracing.com/forum/index.php/topic,5612.195.html "
Is the Cp for this rear engine roadster between the driver and the rear axles? 

I noticed you use Solid Works 3D CAD, do they also make the CFD program you use?  I've looked at ( well looked up)  Autodesk Inventor and ALGOR their CFD program. Hoping I could get a student versions, this stuff is a _little pricey_ and I don't know what I am doing.  To give you some idea of "how deep the dive" I am planning is.. I have gotten pretty handy at Delta CAD a low buck 2D cad program similar to Microsoft Paint.  : ]  Just itch en to learn solid modeling so I can run that though a CFD program. However most of what I know about a wide variety of software was learned by downloading and point and click (what does this do?).

"there is another book, but it needs to be treated with caution.

Goro Tamai: The Leading Edge."

These hyper efficient shapes have little or no lift + or - at all right?

And here is where I put my foot in the bucket..  Here is where my permanent day dream is heading. To beat 325 in the mile with out building a 5000hp, 5000lb, Top Fuel Streamliner,    ( if that would do it) a very light, near 0 lift body using _active_ front and rear high aspect wings.

I hope ya'll didn't just spit you coffee on your screens and key boards Laughing Your Arss's off.  Maybe the laughter will help you through your Monday.

Breck (I am so far in over my head, Domino's would need a submarine to deliver me a pizza, but I am really enjoying the descent)

Offline Rex Schimmer

  • Hero Member
  • *****
  • Posts: 2625
  • Only time and money prevent completion!
Breck,
The dreaming is just the first part of the whole landspeed racing trip. We all dream, we all feel we have a better idea and if we are really bitten by the salt bug we actually may get to the point where we are building something. You learn along the way, listen to the guys on Landracing, especially the guys that have been doing it for a while, tremendous knowledge and they can keep you out of the $h=t.

Try this web site for low buck CFD, there was an article about them in the January 2011 Racecar Engineering. www.symscape.com.

Rex
Rex

Not much matters and the rest doesn't matter at all.

Offline Breck

  • Jr. Member
  • **
  • Posts: 32
Hello Rex

Thanks for the encouragement. 

"listen to the guys on Landracing" "tremendous knowledge "

Man are you right about that,  I'm learning tons of stuff in this forum. I've been prowling around in the archives and I can get lost in here for hours, one thread leads to another thread, then a link, then another...  Build diary's are the Coolest stuff ever.  I think I'm getting little brain blisters.  : ]

"Try this web site for low buck CFD, there was an article about them in the January 2011 Racecar Engineering. www.symscape.com.

Rex"

Way Cool!  Guess what I'm doing _right now_.  Downloading the demo...

AND found this at Racecar Engineering (second reference to this site in two days, might mean something) F1 cars get variable rear wings,  It looks JUST like I imagined, like louvers opening and closing.  Awesome, here the link:

http://www.racecar-engineering.com/articles/f1/f1-adjustable-rear-wings-how-they-work/
 
Thanks a bunch Rex

Offline Breck

  • Jr. Member
  • **
  • Posts: 32
"Breck, start here: Aerodynamics For Racing and Performance Cars Hp1267 by Forbes Aird ($45~50)"

Found it for $64  and up to $120

"Race Car Aerodynamics: Designing for Speed (Engineering and Performance) by Joseph Katz ($20~25)"

Found this, and I found a 39 page review free .pdf
http://www.strangeholiday.com/oops/stuff/annurev.fluid.38.050304.092016.pdf

Thought I would pass it along.

Later

Blue

  • Guest
Just depends ........ :-o
This is a beautiful illustration of completely separated flow off the back of a low-air-dam vehicle common to LSR.  Yes, it's a NASCAR.  The same situation exists on many LSR racers:  NASCAR sacrifices drag for competitiveness (like a restrictor plate).  LSR needs to be more concerned about the flow under the vehicle and how this fills in the area off the back of the car to create less drag vs. the downforce available.