Under floor flow & diffusers

[ArgyrisB]

I say that there is a drop in the velocity because of the continuity equation. under the car we have small volume, but in the area of the diffuser this volume is increased hence the velocity drops.

I think you are right about the pressure potential but i found that here: http://www.formula1-dictionary.net/diffuser.html

[chuckdanny]

From your link

" The diffuser is by the rules, located behind the rear axle line."

Right and there is a good reason for that, the tires create a real throat ahead of the so called throat of the diffuser which isn't one because we observe no section reduction here... except if you consider looking at it from rear to front.
This improve the good segregation process i was talking about, well thats what i imagine without checking the numbers which is always bold

[chuckdanny]

regarding the diffuser discussion.
The primary purpose of the diffuser is to expand air resulting to drop of velocity and therefore increase in pressure. So it creates a pressure potential which will accelerate the flow underneath the car. However in the previous images we have seen that in the area of the diffuser the pressure is lower than the pressure underneath the car not higher as one would except.
What's the explanation, cause i've been confused

Sorry i misread, your confusion comes from the fact that there are 2 two distinct area, the throat or inlet and the outlet.

You say : " However in the previous images we have seen that in the area of the diffuser the pressure is lower than the pressure underneath the car not higher as one would except"
Which is contradictory for you with that :
"The primary purpose of the diffuser is to expand air resulting to drop of velocity and therefore increase in pressure"
Which happend at the outlet, so pressure is lower at inlet end back to freestream at the outlet.

I correlate qualitatively my numerical experiments with real tunnel flowvis and thanks to my very clever tool, more than i am, it is very good !

A Transat chair in ground effect:

The real thing (upper image):

[chuckdanny]

And a stalled diffuser corresponding to the lower picture :

[ArgyrisB]

Firstly i'd like to thank you for your answers! Ok now it seems i get it.
So it is the throat that drops the pressure resulting in a sucking effect under the body?
but teams back in 2010 seemed to focus on expansion of the air with the double deck diffusers, so what is its purpose?

[chuckdanny]

For me no! It's the fact that there is a step, let's say a vacuum (which appear only with compressible flow, in fact a low pressure area) forming which is further increased with rake where this vaccum form all along. Furthermore you can see on the transat chair effect that in contradiction with what is said sometimes there is no side leak, it's the opposite, the gap sucks also the air coming from the sides hence creating a big vortex so the problem is more to control the section reduction that it creates (look at the squeeze section). This process grows massively when i add squirt, a sideshield and this vortices create big downforce on their own.
I can imagine the benefit of this process, you don't need streamwise velocity anymore so matching upperfloor speed with underfloor is easier... or not... there is a tradeoff somewhere...

But your question was about double diffuser, in fact it hads another extractor (not throat, no section reduction) to double the effect (and o course it's corresponding outlet), i'm not sure but i think the added inlet of this double diffuser was not oriented perpendicular to the flow maybe extracting air from thoses vortices... Something to check though...

My transat chair in ground effect with skirt!


And without to compare

[chuckdanny]

As a boring season started (until the wake up of mclaren/honda) i tested for you the dented flap !




it seems to work well, no more stall and more static pressure recovery on the back of the flap so less drag although the main plane work on an extended surface which could undermined the positive effect on the flap

[chuckdanny]

reading an excellent paper about vortices system created by the front wing endplate, i learned that depending on how vortices are generated it can have axial velocity greater than freestream (up to 4 or 5 times greater), i thought it was the opposite, always lower axial(streamwise) velocity, creating a real jet effect like exhaust but of course with less strength, i didn't check on my bird... maybe...
I always thought it could go up to the same speed but greater?? That and the roll up effect would explain how it is working the wing from which it is created harder... hence the effect on the dented flap also.

[SAEED]

Could you please share the paper, Chuckdanny?

[chuckdanny]

yes of course, it's from gordon mccabe excellent blog
http://mccabism.blogspot.fr/2015/03/mcl ... -2003.html

So, while i doubt such a tiny winged object could produce a 400 to 500% acceleration to the flow still the mercedes angry bird must have an effect that partially overcome the standard neutral(almost) flat center section of the wing and accelerate the flow.
There is a kind of "vertical diffuser" or close endplates with footplate just ahead which should enhance the effect and creates another vortex system.

[chuckdanny]

I'm crazy with this thing!
Trying to reproduce the mp4-21 wing-endplate vortex system
This wing was simple enough.



For the moment main vortex is... inexistant, no gurney though, top profil is not sweeping backward, wing not aggressive enough,
Canard vortex is the strongest,
Endplate diffuser vortex is weak but...
Delta winglet vortex weak but its angle is to small and tip misaligned with the endplate upper dent
No footplate vortex

got to improve the design...

[chuckdanny]

F1 is an art !



The art of raising, harnessing the octopus

[chuckdanny]

So, we used to say that the devil is in the details... and suddendly... from a detailed refinement... the devil appear!



Behind the rear wing endplate... hum hum... staring at the chaser it seems.

I wonder... are those rolling devil thunder stormy vortices pulling the stairway to heaven... or is it the stairway (escalator infact here) that further roll the dices.... sorry the vortices...

[dr.ill]

Cool stuff.

What sort of scene are you using to generate those images with the vortices?

[chuckdanny]

A scalar scene with a resampled volum render derived part