Roof Flaps

[A2WindTunnel]

I was just wondering if the air went over where the headlights are that smooth.

It really depends on the CFD program and how fine you mesh the model as to how fine your results and flow visualization.  The finer the mesh the longer it will take to model and compute.  As Rocket123 said, CFD can cost up to $37,000 for a 1 year license and you still have to spend a heap of money on a computer that is capable to run the CFD software.  Plus a PhD. to run the program because it can be very complex to model and analyze. 

To answer your question better, I would expect more separation off the rear and a wake that you don't see in that particular CFD model.  Here is CFD for a stock car and you can notice the huge wake and turbulent air off the back and a high pressure off the front where the air on the ground ahead of the car is affected.  A car without a spoiler would not be as pronounced on the rear, but would not be as smooth as the previous CFD model I posted.  I will also post several CFD models that have finer meshing and illustrate how complex the flow can become in some models.

[Rocket123]

very cool thanks

[A2WindTunnel]

In the Book "The Physics of NASCAR" By Diandra Leslie-Pelecky, Ray Evernham (2008) Chapter 6: The Wizard & The Flying Car Problem (pages 91-104) is an over view of how Gary Eaker worked to solve the lift off problem in NASCAR spins.  It lists the challenges and some of the thought process of what was done to overcome this problem.  Leading him to the idea of the roof flaps and their development.  Pretty interesting reading for those who would like to know more about the history of the roof flap.

Dave

(page 91-104)
http://books.google.com/books?id=OAK3yFlHoTAC&pg=PA93&lpg=PA93&dq=A2+Wind+Tunnel&source=web&ots=UclDdtRpZK&sig=SNLrztXGd5ikWkDttt5uvb5XEnA&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPA91,M1

[A2WindTunnel]

PS: There is a link at the bottom of that if anyone missed it.  I was not telling you to go out and buy the book, but to click on the link and read. 

Link:(pg 91-104) http://books.google.com/books?id=OAK3yFlHoTAC&pg=PA93&lpg=PA93&dq=A2+Wind+Tunnel&source=web&ots=UclDdtRpZK&sig=SNLrztXGd5ikWkDttt5uvb5XEnA&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPA91,M1


Dave

[jl222]

I was just wondering if the air went over where the headlights are that smooth.
LAter

 Yea, and I was going to comment on that o so smooth wake.[pic pg. 3] Maybe nasa ought to go to El Mirage and learn a few things.
 Well maybe they can tell us how come there is no vacuum at the rear of the car.[no drag] Talk about energy savings [no more mideast oil.

                  JL222

Bvillrcr post a video of the real world.







                         

[bvillercr]

The video skips a little, but you can see the spoiler better here than my other video.   

http://www.youtube.com/watch?v=NJZbf4_IUeo

Second video a little more dramatic.

http://www.youtube.com/watch?v=mHUEA-pScY8

[A2WindTunnel]

Yea, and I was going to comment on that o so smooth wake.[pic pg. 3] Maybe nasa ought to go to El Mirage and learn a few things.
 Well maybe they can tell us how come there is no vacuum at the rear of the car.[no drag] Talk about energy savings [no more mideast oil.

FYI: I think that CFD model on pg. 3 was from a university... not from nasa.  A university is not going to have an advanced CFD program or modeler to have a very accurate representation.  I think that is from a student project and would not read into it very much as what the bounding streamlines are really doing on a car like that.  The dust in the youtube videos is an excellent representation of the wake of the car.

 

[jl222]

Yea, and I was going to comment on that o so smooth wake.[pic pg. 3] Maybe nasa ought to go to El Mirage and learn a few things.
 Well maybe they can tell us how come there is no vacuum at the rear of the car.[no drag] Talk about energy savings [no more mideast oil.

FYI: I think that CFD model on pg. 3 was from a university... not from nasa.  A university is not going to have an advanced CFD program or modeler to have a very accurate representation.  I think that is from a student project and would not read into it very much as what the bounding streamlines are really doing on a car like that.  The dust in the youtube videos is an excellent representation of the wake of the car.

 


  The 222 car vacuums up more dust because of the rear spoiler and lower pressure under it [ AR I know you know this but some readers might not] any how have you ever tested a rear overhanging spoiler like a prostock car [15''] or 10'' in our case to measure the pressure difference between top and bottom? Our spoiler measures 10 by 53=530 sq. in". 1 lb less pressure = 530 lbs downforce but have no idea what it really is. I'm sure the prostock guys know.

                            JL222

[jl222]

   I really had a hard time with the above post. It kept posting on its own before i was done!

                       JL222

[A2WindTunnel]

Yes we have and majority of our customers in A2 are race teams that range from NHRA pro-stock to NASCAR which all run spoilers.  I'm not sure if anyone from the teams would be willing to share any data to help answer your question.  All information learned at each test is proprietary to the team and I cannot discuss/post any of their data or findings.  I can generally discuss aero topics and general information to help you guys.  We do have 18 channels of data acquisition available for anyone to run pressure taps on their car.  This could range from incrementing a spoiler left to right positive (+) and negative (-) side, longitudinal or lateral on the car to see what the pressures are doing on the surface at different locations.  All this can prove to be very useful information.

[jl222]

 

[Sumner]

I'm interested in getting more into building and modifying cars, do you have any place that you recommend for a beginner?

Possible ten year later spam post 

Sumner

[Seldom Seen Slim]

Sum, you're the second one to question Mr. Neat's purpose on Forum, so maybe I'll just watch for a little while more and then, as necessary, swoop in with my cursor of death!

[WOODY@DDLLC]

He's a roofer and looking for roof flap repairs?