Aerodynamics Resource Thread

[J. Fast]

Thought it might be cool to start a resource thread for understanding and applying aerodynamics. I was hoping to get a discussion rolling and pool links some of you might have saved in your bookmarks for reference. If you'd care to share them I can consolidate them and build an index on the first page. When you click on this thread in the future, info can be obtained quickly.

A good starting point for discussion might be on the relationship between the undertray and the rear of the vehicle body. What is the "ideal" angle of attack for a diffuser or does that depend on shape, speed, and location of wing? I'm sure there's more than one fluid dynamics and aerospace guru lurking around here?

Link to start this off: http://strangeholiday.com/oops/stuff...304.092016.pdf


Aerodynamics of Race Cars
Joseph Katz

Department of Aerospace Engineering, San Diego State University, San Diego, California 92182;

email: jkatz@mail.sdsu.edu

Should be a good thread!

[Erron Spalsbury]

Aerodynamics, chassis and tyres - Forum - F1technical.net

[BigTyla]

What is the "ideal" angle of attack for a diffuser or does that depend on shape, speed, and location of wing?

Depends on all of these, and it is by no means a simple problem. Diffusers do a good job of increasing overall downforce, but do so at the expense of increased drag. Furthermore, a diffuser that has not been optimally designed can have local areas of DECREASED downforce. These local areas of high static pressure can cause high adverse pressure gradiants that, if significantly high, can lead to flow separation.

[anyonebutme]

not to mention it also depends on the underbody in front of the diffuser as well, and the exhaust exit location.

[Permanent grin]

Is there much benefit for us to flat panel the whole underside? Prop shaft excluded.

I thought the whole point of a rear diffuser was to straighten the airflow out, thus speeding up its journey underneath the car, thus creating 'free' downforce without drag.

André

[Rakuny]

There are a lot of factors to be considered.. A common angle I've heard is 5-10 degrees.. A diffusers effectiveness can be decreased if too much air is escaping out the sides of the car as well. iirc there was an old racing series that ran some kind of flexible side skirts that almost touched the ground to prevent the air escaping out from under the car before the diffuser.

The diffuser and the wing are meant to work together, the goal is to create the most downforce with the least ammount of drag, as with everything there are compromises. Without windtunnel testing, being in the ballpark is all you can ask for.

[Permanent grin]

The flexible sideskirt thing was done in Formula 1 back in the early-mid eighties I believe. As was the revolutionary fan on the Renault car that got banned after only a couple of races because it obliterated the opposition by sucking the car into the track! Nobody could keep up.

André

[Erron Spalsbury]

Yes, flat bottoming would help, as well as venturi ducts but that won't happen on our cars. T-case, prop shaft, exhaust, all that is in the way but we are pretty close as is.
Diffusers, up to any angle you want really, until it stalls. Once it stalls it's just drag. Here's a little secret, angle of the car. Flat is not what you want. Take the entire car and put it on an angle. This is what will net you huge gains in DF.

[Rakuny]

It's a shame this thread didn't go any further. Would anyone be interested in posting up their home-brewed examples and reasoning for aspects of design/effectiveness
What do you guys think about using Alumilite or Dibond sheets for splitter/diffuser making?
Our gas tank is very much in the way as far as having a diffuser goes, would it be better to have a little less angle and be able to extend the diffuser a bit more past the ending of the gas tank? Perhaps Erron can pitch in on this as I have seen his diffuser and know it starts where the gas tank ends. What was your reasoning behind this? did you consider it differently but change your mind, why?

[Erron Spalsbury]

That's good material for sure.
I basically wanted to bridge the gap between the bumper and gas tank. It starts at the front of the gas tank too.