Aero questions

[SvdM]

Hi there, I have a couple of questions I would like to bounce off of you guys.

01

I have noticed that there is quite a bit of space in some of the exhaust tunnels and wondered that if one was able to add tubing to duct air more efficiently through there (thus not increasing FA) from part of the radiator to the rear of the vehicle. Would a ram-effect of incoming air be strong enough to carry air at a higher pressure than atmosphere to help fill the low-pressure at the back of the vehicle or would these gains be quite negligible?

I know there would still be losses, but if this system was well made, would one be able to supply the rear with more litres of air than a normal clean underbody would?

[Frank Lee]

Since energy is being added in the form of heat it should theoretically be able to add thrust or perhaps at least be thrust neutral. I suspect the effort is not worth the potential gains.

[Angelus359]

are you suggesting closing off the buttom completely, except for a tube to allow air that bypasses the radiator opening gap?

Interesting...


I actually had an idea of piping my air intake to assist with cooling the radiator :P

Off the filter box run tubing to the radiator, and then have it run face first into it, sucking air THROUGH the radiator

The more power you suck in, the faster the cooling... slightly

Another option would be to just use a cone air filter sitting behind the radiator with the box open and then behind the radiator have a 4 inch opening in the under coating to allow air exit.

The piping idea is a viable option.

[SvdM]

Stated slightly differently:

This will make more sense at highway speeds. I suspect that this effect happens to some extent to people using full undertrays already anyway, as some air gets forced down the chassis tunnel because of it not being able to then go elsewhere.

Now, since we all need to use some incoming air to cool the radiator and that air will be at a higher pressure and need to go somewhere, would it not make sense to duct this slightly higher pressure (and warmer) air to the rear without adding to the frontal area.

I'm inclined to agree with Frank, but then again, I don't now how much air this ram effect will be able to send to the back of the vehicle without necessarily adding to wind load.

Pardon, I couldn't remember the thread, but someone posted a CFD profile of their Mk4 Jetta and just for fun, poked a hole through it and the drag at the rear of the vehicle dropped dramatically and I started wondering what something like this would look like in practice on a vehicle used daily (not some special Bonneville racer or similar).

[aerohead]

Originally Posted by SvdM

Hi there, I have a couple of questions I would like to bounce off of you guys.

01

I have noticed that there is quite a bit of space in some of the exhaust tunnels and wondered that if one was able to add tubing to duct air more efficiently through there (thus not increasing FA) from part of the radiator to the rear of the vehicle. Would a ram-effect of incoming air be strong enough to carry air at a higher pressure than atmosphere to help fill the low-pressure at the back of the vehicle or would these gains be quite negligible?

I know there would still be losses, but if this system was well made, would one be able to supply the rear with more litres of air than a normal clean underbody would?

Dr,Alberto Morrelli analyzed the cooling system drag of the CNR "banana car" and reached a drag minimum after four short exit ducts were positioned and channeled such that air would join the surrounding low pressure airstream at the same velocity so as not to trigger separation.Internal duct losses were kept to a minimum by the short runs.
Ford and GM concept cars go ahead and simply move the radiator to the back of the car so it may exhaust into the low pressure wake.
If you'd like to research duct losses,you could get a hold of an ASHRAE Manual.

[curv872]

Are you thinking along the lines of a blown diffuser used in F1?

[SvdM]

I had to search to see what you're talking about, but YES.

I didn't even know they do this in F1... F1 used to be on a free TV channel, but hasn't been for quite some time now and so I've lost interest.

[botsapper]

Very ambitious proposal, for ordinary performance envelop. For racing purposes some have pushed those limits for ultimate grip with the help of vacuum fans instead of diffusers & huge wings. Chapparal 2J, extracts air from underneath, maintains constant low underbody pressure and achieves more road-handling grip. Another one, Gordon Murray's Brabham BT46B, combined all aero devices, a rear fan unit with canards & rear wings. It won its debut race but was then quickly banned. 100% winning record. His excuse is that it was an engine 'cooling' device, right.
Another evolution in ultimate racing aero is being developed by 2010 Constructors Champion, Red Bull Racing - Adrian Newley. Yes, it is vaporware but it is an example of a real F1 engineer's unlimited imagination w/o the current regulations. It's actual limitations are the driver's physical limits/abuse caused by its performance lateral forces.
Red Bull X1 Prototype Gets Real, Set to Debut in Madrid

http://www.youtube.com/watch?v=nu5UvgIcMOg

As for 2010 FI 'moveable' front vent controversy, it really lowers top speed drag.
F1 aero updates, Bahrain | Formula One 2010 | F1 | Racecar Engineering