BuffDaddy915

lmao!

BATMAN

Think they make an automotive Prep H for Diffuser Homoroids?

maxcooper

Perhaps the 360 diffuser creates less drag than whatever they were going to do at the end of the car before. I understand that you can't get something for nothing, but every case of car aero would seem to start with a car that is already far from optmal in design. It seems quite possible that you could both reduce drag and increase downforce on just about any production car ever built.

-Max

HedgeHog

I don't think diffusers can create drag. Contrary to that, it only reduces drag. On a wing, the angle of attack will cause the underside of the wing to create vortices and the swirling air makes a pocket which is low pressure...thus drag. Also, the hole it punches causes wind resistance. Taken into context of a car, the bottom of the car is the bottom of the wing. The diffuser should cause the lower air flow to smoothly rejoin the top flow over the car thus minimizing the turbulence; keeping the laminar boundary layer intact promotes drag reduction.

also, i think negative lift is slightly diff than downforce. one sux the car down and the other pushes. I seem to recall reading that negative lift characteristics from diffusers have drag issues than downforce via wing/spoilers.

where the hell is stephen lee when u need his doctorate diatribe?!

damian

iTrader: (2)

im diggin this thread... good info on diffusers and aero

pomanferrari

iTrader: (1)

Batman, are you sure it was a female?

Mr. Stock

Interesting way to put it BUT,
how does the "sucking" occur?
It has to do with pressure gradients.
With a diffuser, the pressure is lower below the car compared to above it. So the net effect is downforce on the car.

Which is what happens with a wing as(Well, you can say that the pressure is higher above the wing/car than the pressure below it - but the net effect is that there is a pressure gradient resulting in downforce).

So in reality, "negative lift" is the same as downforce.

DamonB

Diffusors do create drag. Much less than a spoiler or wing, but it's still there. If you are going to do anything that changes the energy of the air (such as slow it down) you're going to cause drag. It's that simple. Don't confuse efficiency with lack of drag. Efficiency is a grade for how much you get out for what you put in so to speak. Properly desinged diffusors and wings are much more efficient than a spoiler for instance, but they do create drag. At the same time for any given design if you decide to make more downforce from it you're going to get more drag. That's the way the universe works.

Think about this for a moment. If you could make shapes that could derive energy from the air without causing drag than you could design an aircraft that once accelerated to speed no longer needs an engine. Ain't going to happen. For that to happen you would be inventing "free" energy and that does not exist.

The only thing free on this planet is gravity. If you want to do anything other than plummet to the center of the earth it's going to take some other forces which require energy.

Racecar Aerodynamics: Designing for Speed by Joseph Katz.
available here

Competition Car Downforce by Simon McBeath
available here

Mr. Stock

'Tis true.

BATMAN

ACtually it may have been urs when u passed out from Kool-Aid on ma bed........

HedgeHog:

The wing has a push and pull effect.

wind pushes the top part down and the bottom part pulls it down.

Diffusers just pulls it down, hence the reduced drag.

DamonB

The diffuser has reduced drag because it is a "void" that the air is flowing through rather than an object it must strike and then move around. The diffusor causes less of a disturbance than the wing because of this along with the fact that the diffusor also accelerates the air at the rear. This makes some thrust. Not enough to overcome all the induced drag, but enough to make net drag less than a wing.

Wings do not push/pull at all. All they do is create an area of low pressure above the wing (airplane) or below the wing (car). The diffusor operates exactly the same way except that one side of the diffusor is actually the car rather than a seperate assembly like a wing would be.

BATMAN

I meant to say the rear wing/spoiler.

HedgeHog

If that were the case, the the diffuser would be a useless device. The point of the diffuser is to spread out the air after it has been compressed - this allows the lower laminar flow to join smoothly back with the top laminar flow to reduce turbulence. A void in the air would imply that the air vanished.

So if a diffuser causes drag then one would conclude that without the diffuser, there will be even less drag.

DamonB

I don't mean the air vanished, I mean you have a "hole" traveling through the air rather than an object like a spoiler or wing. The only frontal area the diffusor presents is the approach to the throat.

Yes. An object that was perfectly streamlined (generates the least drag possible) would not have anything resembling a diffusor.

TAMAatWork

Is the rear defuser on the red car the same as this here?

http://jt-imports.com/Chen_rear.jpg

If so, how much and does it over lap a bit on either side of the rear bumper?


Thanks,
Joseph