aerodynamics discussion in chassis engineering
 

http://e30m3performance.com/myths/splitter/splitter.htm

i'll come back to this later gotta run...

A+ great post!

http://e30m3performance.com/myths/sp.../splitter2.gif

ok so here we see what the typical air flow looks like at the front of a car and where the subsequent high pressure zones would be.

note that it is nice to source brake ducting air from these high pressure areas.

http://e30m3performance.com/myths/splitter/venturi.gif

now notice here that not only is it important to catch air above a splitter to create downforce but also to expedite air underneath in order to maintain uniform flow and what not.

notice at the back end of the vehicle, the bird tailing of the undercariage air flow, this must rejoin with the overcar air flow and as such you see many times that race cars curve their rear paneling upwards.

isn't another theory to keep as much air out from underneath as possible? using dams, or is that a rules play?

i had this really great paper before and it was about two stanford engineers and their experimentation with two dimensional diffusers and their subsequent critical values of flow seperation and what i will refer to as reverse flow turbulence. they did this by setting up clear plastic ramps over which they flowed water. they would make clear walls that would make a channel then seperate the walls to create a diffusion in the flow.

what a rear underbody diffuser does is it prevents flow seperation. what the engineers found was that at certain critical fluid speeds the diffusing flow would curl. you can imagine this,

if a stream of water is in a channel shaped like this:

@@|......|
@@|......|
^@/........\
@ /...........\

and the water is flowing down then it will diffuse to fill up the "triangle" part of the channel. if hte triangle area is too wide... the water will not be touching walls anymore and at the edges of hte flow there will be flow seperation where the flow gets very turbulent and disruptive, curling back on itself and making things very ununiform and slowing the overall flow down.

picture a garden hose, when under high pressure the water that comes out fans, and the water on the outter most parts is going LOTS slower than the middle stream.

so what did they do? they put slats in. the slats prevent the outter edge fluid from curling on itself... it will curl into the wall and then keep going.

of course this looks different in a flat flow than it does in 3d. the horizontal component from curling on itself and the verticle component either hits the ground or curls up to rejoin with the overcar fluid.

the gurney flap

http://www.allamericanracers.com/gurney_flap.html

the gurney is used to reduce flow seperation at a certain critical air speed over a wing. hte top and bottom flow must rejoin in order to minimize drag.

mmm you definitely want to keep as much air away from underneath the car as possible. some rules don't allow you to but in a rules barred vehicle you could.

that said you'd have to keep hte air out of ALL of the vehicle. keeping air out in front and letting it come in the sides isn't that helpful.

i hate the fact that i can't find pictures to describe what i want to convey. i can draw the pictures but the lack of a permanent type of hosting is really annoying.

anyway onto discussing the double wing, double-decker wing, slotted wing etc. everyone has seen this on the back of some civic that didn't need it. many have laughed at them. the fact is this is one of the best ways to gain more downforce without drag inducing flow seperation.

what happens is the first wing seperates the flow top and bottom, when these two rejoin you can increase the angle of attack as the rejoining flows are faster than the original flow. this then feeds the second wing which seperates those flows and in that way the tail flow is sufficiently fast to not seperate and this combination creates more downforce.

http://public.cranfield.ac.uk/me/me0...Newton2004.pdf

start looking at diagrams after page 75. if you choose to read this thing you'll be better versed than me.

http://www.dcetech.com/nitish/reports/formula1.htm

take note of the picture of the see through wing.

next up is naca ducts.

Just thought I'd add something about the splitter and gurney flap (sort of).

These two you can get from Mitsu in Japan:

https://i47.photobucket.com/albums/f...8nwy/front.jpg
^this is kind of a front lip, but is recessed in slightly (by about 1" from the very front edge). Extends downwards by about 1.5-2". Does not go as far down around the centre. There's a metal backing to it, but the lowe half is rubber.

https://i47.photobucket.com/albums/f...38nwy/rear.jpg
^difficult to see from here, but it's a sort of mini-gurney flap. It's section is like a capital 'B' and is about 3/4 the widht of your finger in height. Sticks on the rear edge of your rear wing.

I actually got these two for a rather special price from Japan. I had doubts that they would work, but after installation, my top speed is certainly harder to reach, which at least means that they're having _some_ effect, even if detrimental!! But seriousl, the car feels more stable at silly speeds, it's not very pronounced, but it is detectable. Obviously these aren't really meant to make night and day difference, but I can assure you that even with these very small changes, there is a difference. I don't really know g numbers with/without, but I think the front has more effect though...

Here are some further examples aerodynamic mods that are commonly used across the board and of course work well on the Evo...

https://www.evolutionm.net/forums/sh...d.php?t=167941

Here are some double deck wings, splitters and... well, I don't know what you call them.

I'm sorry. I'm very sorry.

i actually meant air flow diagrams... like the ones in the pdf hah

oooh excellent posts....this is coming from an Aerospace Engineering student.


Excellent article in Racecar Engineering about simply taping up the gaps on the front bumper/grill/hood. The reduction in drag and increase in downforce was pretty interesting.


Trinydex i can host some pictures if you want. PM me.


- Andrew

yeah that sounds great.

Hmm. Too bad the Evo doesn't have that. Oh, wait...

http://i6.photobucket.com/albums/y24...o/Rearwing.jpg

;)

--Dan
Mach V