Stalling Diffuser

[PNSD]

I cant see how that works tbh.

If the rear wing basically merged and became one element and stalled that cause a huge increase in drag.

I really dont understand how it would be possible to achieve less drag with a stalling wing.

Definition of stall is the seperation of airflow resulting in little pressure differential, loss in downforce and huge increase in drag.

[kilcoo316]

the idea of stalling diffusers isn't absurd at all.

Trust me - its absurd.

If you recall the 'hot' topics from a few years ago, you will remember that the whole concept of a flexible rear wing was to flex at high speed, resulting in the closing of the gap between elements. This effectively made the rear wing a highly cambered, single-element device as opposed to a 2- or 3- element one, resulting in stall. This reduced drag as a result and gave cars a higher top speed.

I know. It was actually a cyclic stalling as the 2nd element loaded and unloaded from the stall.


But the two are not comparable.


The diffuser stalls due to distance from the ground*, while the rear wing stalls purely based on air speed.


* this can be a result of simple aero load down a straight (dependant on airspeed), or compression due to bumps or track curvature.


You can control the stall due to airspeed only. But you cannot control the ride height (and rake angle( through a corner like eau rouge or 130R to the same tolerances.



PNSD - the reason the stall reduced drag is simply the load vector of the 2nd element. If we simplify it and say the aero load created from the pure aerofoil lift/downforce is normal to the chordline of the aerofoil itself, look at how steep the 2nd element is - probably at 60 or 70 degrees to the horizontal - so in effect, the majority of its 'downforce' is actually acting as drag.

Sounds strange, I know, but thats the way it is.

[bettonracing]

Trust me - its absurd.

[-X
http://www.autosport.com/news/report.php/id/57511
Start @ the 5th to last paragraph.

There is also evidence of it in other motorsport categories.

Regards,

H. Kurt Betton

[rjsa]

Wasn't the moveable floor from Ferrari about choking the air flow underneath the car, stalling the difuser?

EDIT: Kurt you beat me to it, I hadn't followed the link.

[tahadar]

I cant see how that works tbh.

If the rear wing basically merged and became one element and stalled that cause a huge increase in drag.

I really dont understand how it would be possible to achieve less drag with a stalling wing.

Definition of stall is the seperation of airflow resulting in little pressure differential, loss in downforce and huge increase in drag.

just to clarify something. Drag can be broken down into two parts: D = Do + Di where Do is the form and skin friction drag contributions, and Di is the induced drag. induced drag is a function of the lift coefficient squared, so upon stalling as the lift rapidly drops, the induced drag significantly drops.

as to the argument about the 'ridiculousness' of the stalling diffuser, i think the autosport article speaks for itself..

[kilcoo316]

Trust me - its absurd.

[-X
http://www.autosport.com/news/report.php/id/57511
Start @ the 5th to last paragraph.

I disagreed 100% with it then - and I maintain that now.

The flexible floor was a way to run more agressive rake angles, and get more from the floor - not less.



You DO NOT want to stall the diffuser. The downforce it creates is relatively free of drag anyway. It is very much affected by proximity to the ground plane, like the front wing, and is an essential part of car balance at high speed.


The rear wing you can work with as it doesn't change its performance with proximity to the ground. (That really means its downforce varies only as a function of airspeed squared - while the front wing and floor vary with airspeed squared and rideheight)

[kilcoo316]

Wasn't the moveable floor from Ferrari about choking the air flow underneath the car, stalling the difuser?

No. But it was mis-interpreted as that.

[Fil]

"...the Ferrari floor could lift at high speed leading the diffuser to stall. This could either increase straight-line speed through a loss in drag, or improve the car's balance by reducing rear downforce."
what i don't understand from that article is how a car that has its balance optimised for the track, would need to have this adjusted for straight parts of the track, by removing downforce from the rear.

adding to that. would not this adjusted balance cause handling issues in fast sweeping turns. eg Suzuka's 180r or Spa's Eau Rouge or Copse at Silverstone, where balance and downforce from the diffuser is needed?

doesnt quite make sense to me.

[bettonracing]

[-X
http://www.autosport.com/news/report.php/id/57511
Start @ the 5th to last paragraph.

I disagreed 100% with it then - and I maintain that now.

The flexible floor was a way to run more agressive rake angles, and get more from the floor - not less.

Well I hate to tell You but You were wrong then annd You're wrong now. The spring is at the front of the floor. You CANNOT create MORE rake using the spring at the front of the floor without sticking the edge of the floor into the airflow (tremendously counterproductive). See the pics in the article and other pics (of the actual cars' floors) floating around the net.

Regards,

H. Kurt Betton.

[kilcoo316]

The spring is at the front of the floor. You CANNOT create MORE rake using the spring at the front of the floor without sticking the edge of the floor into the airflow (tremendously counterproductive).

Please explain how running the splitter plate closer to the ground... infact, running it in contact with the ground and bending it (effectively moving the rearmost point where the front floor is in contact with the ground backward) does not induce a greater rake angle over the rest of the floor.

I'm most interested to hear how you manipulate trigonometry.




It is the step-plane that is providing the majority of ground effect* - the low pressure area under the plank is quickly filled by higher pressure stuff either side of the step. A cursory glance at the boat-tail at the back of the plank indicates this.

*especially when the plank grounds out!

[bettonracing]

http://picasaweb.google.com/bettonracin ... 8659858834

Moving the floor downward would have the frontmost edge of the floor protruding into the wind.

The deflection test related to the flexing floor 'saga' was an upward force applied to the chassis 'floor'.


Regards,

H. Kurt Betton

[kilcoo316]

Pitch man... its all about car pitch. You know what rake angle is - c'mon!


Forget about the floor being flat and horizontal to the ground.


Here is what is happening:

[bettonracing]

That makes more sense than what I thought You were saying. I won't refute Your interpretation works as well (although it could be counter productive to run @ high speed with the softer wheel spring rates required). However I will continue to refute that 'stalling' diffusers (i.e. passively manipulating diffuser airflow) is absurd.

Consider aerodynamic interactions and rolling resistance (as influenced by the diffuser).

Regards,

H. Kurt Betton

[rjsa]

But wouldn't the floor/track opening choke at a given speed/tight entrance combination? Then it would be like you had some kind of skirt sealing the air entrance?

[Astro1]

I don't think that the idea of a staling diffuser is absurd, but it would be impractical as the stall would have to not be passive. At different tracks it would cause huge problems when going through fast corners when the diffuser generating the bulk of your downforce, suddenly says no more. Even if the diffuser's stall function was controlled by driver input, electronics, etc and not some preset it would still be impractical.

I think that before we have stalling diffusers, will have stalling wings if anything. The diffuser is one of the greatest downforce generating tools, in that it does so at the minimalist of drag penalties. The wings on the contrary are sails in terms of drag compared to the diffuser. So if you want anything stalling it would be the wings as there you can actually gain down the straight by reducing drag. Stalling the diffuser will give you little in terms of drag reduction and a whole lot in terms of loss of downforce which makes no sense when you try to apply the idea.

Look at it this way. The idea, is nothing new and or unexplored. Can it be done? Easily. If it was practical it would already be in use.