Fascinating stuff speedsense!

I must admit I thought you were joshin’ for a moment when you said the diffuser “does not work as a diffuser”.

”this can be easily seen by removing the wings on a car, and keeping the diffuser. Then replacing the wings and removing the diffuser and recording the results all in a windtunnel”

Have you done this, or heard it being done; or are you speculating what might probably be the case? The rear wings are pretty puny these days.

Windsor mentioned during the Singapore race that he was talking to guys in the paddock who stated that downforce can be broke out: 50% under car, 30% front wing area, 20% rear wing.

Since the majority of the underneath of a car is flat, I assumed the numbers were driven primarily by the rear diffuser – and other unknown secret stuff somehow concocted outside and around the FIA skid block.

Where does that hefty 50% number come from then if not the rear diffuser?

In looking at the complexity, and the changes that are being made (here and here), I can see how all the baffles (and flanges at the rearward end of the various tunnels) might be used to extract (inflect?) more air out of the diffuser (benefits outweighing their increase drag) but you are saying that all the extra low pressure generated by tricking more air out from under the car is NOT significantly pulling the bottom of the car down by the diffuser surface, like a wing, but allowing the otherwise static rear wing downforce to push down further into a low pressure zone. True?

I see there are also directional louvers under front wing. They look square/vortex looking… and just under a wing. Makes sense!



The second improved one below shows the roundness of the upper double diffuser. Does your square=vortex notion stand for this design too?



I’m a simple soul. I think of a kid’s balloon sitting here on the table – and me not blowing on the balloon itself, but behind it to create low pressure area, which in turn moves the balloon. Since the double diffuser (in the case above, round, like my lips) and pointed slightly UP, it seems to be trying to create negative pressure just behind the lower (and upper) rear wings. Makes sense. My balloon would agree.

(I would be interested to know the downforce improvement created by the upper round DD % on that close lower rear wing vs. the % upper rear wing.)

But then why not just have one big funnel up – like the original Ferrari single diffuser? Does not GreyWolf74’s slot-effect point make perfect sense (speeding up the air through the ducts) since we consistently have two distinct ducts in a double diffuser? So your point/logic stands – totally – but the “double” part of the double diffuser might also be bringing more to bear – adding to your point – via speedier air?

speedsense - 22 October 2009 11:16 AM

A perfect example of the use of vortex generation can be found when ground strakes on ground effect tunnels were outlawed and an air gap was created from the side pod to the ground. Vortices were used to "help" replace the sealing effect of the strakes and prevent intervention from outside air streams as well as escaping air streams from within.

SS, something you might find interesting, speaking of vortices sealing tunnels......

On the GTP car I worked on in the late 80's, early 90's, we took it to Daytona for the first time, and experienced 'porpoising' going down the backstraight. After trying a few things to determine the cause, we discovered that a bit less rear wing or a bit more rear spring or rear ride height solved it. Turned out that the reduction in rear ride height at high speed (160mph plus or so) was just enough to reduce or eliminate the effectiveness of the vortices that ran down the side pods, sealing the undertray......... the seal would go away, the car would rise and the seal was reestablished, the car would quickly suck back down to where the seal would go away again, over and over and over......

I also believe that the front wheel covers in F1 these days contribute to this side floor sealing effect, and is their primary purpose. Of course, I could be completely wrong.

ipso - 22 October 2009 02:41 PM

Fascinating stuff speedsense!

[quote=I must admit I thought you were joshin’ for a moment when you said the diffuser “does not work as a diffuser”.

”this can be easily seen by removing the wings on a car, and keeping the diffuser. Then replacing the wings and removing the diffuser and recording the results all in a windtunnel”

Have you done this, or heard it being done; or are you speculating what might probably be the case? The rear wings are pretty puny these days.

Yes, I have and also done extensive testing on ground effect tunnels.

Windsor mentioned during the Singapore race that he was talking to guys in the paddock who stated that downforce can be broke out: 50% under car, 30% front wing area, 20% rear wing.

The 50% underneath comes from reduction of lift (high pressure) which causes the upper surfaces, body, spoilers and wings etc., to exert more force downward.
Aerodynamics tells us that a flat bottom close to the ground is a high velocity/low pressure area (good thing for a race car). Though neglects the presence of rotating tires/wheels (virtual air pumps), front wing wakes, suspension pieces and body parts..all which create turbulence that end's up under the car, creating high pressure pockets in the stream. Also ground undulations and the stepped bottom all play a part in the introduction of high pressure areas present where theory tells us it shouldn't be. This all creates lift, and counters the wings (and the other upper body devices) ability to produce the highest possible downforce (wings) or downward forces (body panels, spoilers,non wing gurney lips etc.).
A diffuser acts as scavenging device to "help" remove these high pressure areas with the "mouth" of the diffuser drawing in the high pressure areas...

Since the majority of the underneath of a car is flat, I assumed the numbers were driven primarily by the rear diffuser – and other unknown secret stuff somehow concocted outside and around the FIA skid block.

answered above

Where does that hefty 50% number come from then if not the rear diffuser?

Technically the bottom of the car or the diffuser isn't creating downforce, it's reducing lift allowing the upper elements to create more force....

In looking at the complexity, and the changes that are being made (here and here), I can see how all the baffles (and flanges at the rearward end of the various tunnels) might be used to extract (inflect?) more air out of the diffuser (benefits outweighing their increase drag) but you are saying that all the extra low pressure generated by tricking more air out from under the car is NOT significantly pulling the bottom of the car down by the diffuser surface, like a wing, but allowing the otherwise static rear wing downforce to push down further into a low pressure zone. True?

Not quite by "tricking" but yes. High pressure in a ground gap (between floor and ground) has a huge amount of strength in countering downforce or downward force numbers.

I see there are also directional louvers under front wing. They look square/vortex looking… and just under a wing. Makes sense!



The second improved one below shows the roundness of the upper double diffuser. Does your square=vortex notion stand for this design too?

A ninety degree angle is one of many routes to creating vortices. V angles, "check mark angles", shark teeth cutouts, partial venturi shapes, oval venturi shapes, gurney lips... many shapes can create vortices....



I’m a simple soul. I think of a kid’s balloon sitting here on the table – and me not blowing on the balloon itself, but behind it to create low pressure area, which in turn moves the balloon. Since the double diffuser (in the case above, round, like my lips) and pointed slightly UP, it seems to be trying to create negative pressure just behind the lower (and upper) rear wings. Makes sense. My balloon would agree.

(I would be interested to know the downforce improvement created by the upper round DD % on that close lower rear wing vs. the % upper rear wing.)

But then why not just have one big funnel up – like the original Ferrari single diffuser? Does not GreyWolf74’s slot-effect point make perfect sense (speeding up the air through the ducts) since we consistently have two distinct ducts in a double diffuser? So your point/logic stands – totally – but the “double” part of the double diffuser might also be bringing more to bear – adding to your point – via speedier air?

Speeding up air in duct, does exactly what?
Your garden hose with water running through it is high velocity/low pressure with the only force produced coming from the spray out the end of it.
Though the second tier diffuser of the Brawn, Red bull and Mclaren isn't this way. The ducting inlets are far smaller than the outlet. Unless there's air coming from some other location, the volume of the ducting area is increasing as the air goes downstream (this slows velocity and increases air pressure) not the ingredients for downforce production.
When you look inside these compartments, note the shape and size vs the inlets size shape and the outlet shape/appendages(lips,v cuts (Ferrari had some).
And in your mind's eye flood it with water traveling at high speed, something like a garden hose with it's nozzle on backwards and shaped like some sprinkle you might have, at the out let....
Still think it's a secondary wing or the upper surface of one? Doesn't look like any one I've seen
IMHO

wilmywood8455 - 22 October 2009 08:24 PM

speedsense - 22 October 2009 11:16 AM

A perfect example of the use of vortex generation can be found when ground strakes on ground effect tunnels were outlawed and an air gap was created from the side pod to the ground. Vortices were used to "help" replace the sealing effect of the strakes and prevent intervention from outside air streams as well as escaping air streams from within.

SS, something you might find interesting, speaking of vortices sealing tunnels......

On the GTP car I worked on in the late 80's, early 90's, we took it to Daytona for the first time, and experienced 'porpoising' going down the backstraight. After trying a few things to determine the cause, we discovered that a bit less rear wing or a bit more rear spring or rear ride height solved it. Turned out that the reduction in rear ride height at high speed (160mph plus or so) was just enough to reduce or eliminate the effectiveness of the vortices that ran down the side pods, sealing the undertray......... the seal would go away, the car would rise and the seal was reestablished, the car would quickly suck back down to where the seal would go away again, over and over and over......

I also believe that the front wheel covers in F1 these days contribute to this side floor sealing effect, and is their primary purpose. Of course, I could be completely wrong.

Yep, two of the most important aspects to ground effect a)center of pressure location within the tunnel and b) the gap of the sides to the ground.
I also believe the wheel covers are "moving" barge boards

speedsense -

Speeding up air in duct, does exactly what?
Your garden hose with water running through it is high velocity/low pressure with the only force produced coming from the spray out the end of it.
Though the second tier diffuser of the Brawn, Red bull and Mclaren isn't this way. The ducting inlets are far smaller than the outlet. Unless there's air coming from some other location, the volume of the ducting area is increasing as the air goes downstream (this slows velocity and increases air pressure) not the ingredients for downforce production.
When you look inside these compartments, note the shape and size vs the inlets size shape and the outlet shape/appendages(lips,v cuts (Ferrari had some).
And in your mind's eye flood it with water traveling at high speed, something like a garden hose with it's nozzle on backwards and shaped like some sprinkle you might have, at the out let....
Still think it's a secondary wing or the upper surface of one? Doesn't look like any one I've seen
IMHO

What does running a second source of high speed air do for you? It creates a siphon drain. It's a very simple T-shaped device used to drain water from a pool, tub, vat or whatever, by connecting one source of flowing water to one side of the cap on the "T" and using that flow to draw fluid through the base of the "T" and out the other side of the cap.



Here's how it works:

A high-velocity, high-volume stream of fluid (usually water), shown in red, enters the "T" at the end marked "G 1¼." This tube, labeled "Φ31.8" is sealed inside the larger main body, which is labeled "Φ 49.5". As fluid flows through the tube, it creates a vacuum in the larger "Φ 49.5" main body, in accordance with Bernouli's principle -- fast-moving fluid has less pressure than slow-moving fluid.

Note how that inner "Φ38.1" tube is open to the larger chamber at the other end. That causes a partial vacuum in the larger chamber.

Next, note that the second pipe, also labeled "Φ38.1" x 300 long is connected to the main chamber but not the inner tube. There is a reason for this.

As the flow from the first tube (red) inside the main chamber passes out into the rest of the hose, it creates a partial vacuum, according to Benouli's principle. That draws fluid through the second, right-angle tube, shown in blue. It flows into the larger main chamber and is drawn out the far end along with the flow from the inner tube.

His neat little trick of hydrodynamics works to siphon fluid through the right-angle tube for as long as fluid is running through the inner tube. You can empty a barrell, a swimming pool, or run a spray paint gun the same way.



If you look carefully, you'll see that high pressure air flowing through the spray head draws paint out of the can in exactly the same way. Again, it's another version of a siphon drain, only this time the main tube has a high-velocity air flow pulling on paint.

Ducting air through a "double diffuser" does exactly the same thing. The air flowing through the upper duct comes out of that duct at considerable velocity, creating a low pressure zone. Air flowing under the car, throught he "main" diffuser" meets up with that upper level of flow and you essentially have a siphon drain. In this case, flow through the upper part of the "drain" is drawing more air through the lower part -- the main diffuser -- at higher velocity, which creates greater downforce.

It's a clever way of taking otherwise useless airflow and making it do more work.

GreyWolf74 - 23 October 2009 01:44 PM

[quote author="speedsense" date="1256279881
Speeding up air in duct, does exactly what?
Your garden hose with water running through it is high velocity/low pressure with the only force produced coming from the spray out the end of it.
Though the second tier diffuser of the Brawn, Red bull and Mclaren isn't this way. The ducting inlets are far smaller than the outlet. Unless there's air coming from some other location, the volume of the ducting area is increasing as the air goes downstream (this slows velocity and increases air pressure) not the ingredients for downforce production.
When you look inside these compartments, note the shape and size vs the inlets size shape and the outlet shape/appendages(lips,v cuts (Ferrari had some).
And in your mind's eye flood it with water traveling at high speed, something like a garden hose with it's nozzle on backwards and shaped like some sprinkle you might have, at the out let....
Still think it's a secondary wing or the upper surface of one? Doesn't look like any one I've seen
IMHO

What does running a second source of high speed air do for you? It creates a siphon drain. It's a very simple T-shaped device used to drain water from a pool, tub, vat or whatever, by connecting one source of flowing water to one side of the cap on the "T" and using that flow to draw fluid through the base of the "T" and out the other side of the cap.


Here's how it works:
A high-velocity, high-volume stream of fluid (usually water) enters the "T" at the end marked "G 1

The Red bull, the Brawn and the Mclaren, have an entrance duct, as per the reg's...and they have a exit duct, there isn't a third port connecting to the internal volume of the diffuser to the ducting... otherwise you would be correct in the operation of pulling air from the lower diffuser.
They are only allowed the entrance ports, that I'm aware off.
Additionally the entrance port is followed by a higher volume area which slows air, not accelerate it....

speedsense - 23 October 2009 02:00 PM

GreyWolf74 - 23 October 2009 01:44 PM

[quote author="speedsense" date="1256279881
Speeding up air in duct, does exactly what?
Your garden hose with water running through it is high velocity/low pressure with the only force produced coming from the spray out the end of it.
Though the second tier diffuser of the Brawn, Red bull and Mclaren isn't this way. The ducting inlets are far smaller than the outlet. Unless there's air coming from some other location, the volume of the ducting area is increasing as the air goes downstream (this slows velocity and increases air pressure) not the ingredients for downforce production.
When you look inside these compartments, note the shape and size vs the inlets size shape and the outlet shape/appendages(lips,v cuts (Ferrari had some).
And in your mind's eye flood it with water traveling at high speed, something like a garden hose with it's nozzle on backwards and shaped like some sprinkle you might have, at the out let....
Still think it's a secondary wing or the upper surface of one? Doesn't look like any one I've seen
IMHO

What does running a second source of high speed air do for you? It creates a siphon drain. It's a very simple T-shaped device used to drain water from a pool, tub, vat or whatever, by connecting one source of flowing water to one side of the cap on the "T" and using that flow to draw fluid through the base of the "T" and out the other side of the cap.


Here's how it works:
A high-velocity, high-volume stream of fluid (usually water) enters the "T" at the end marked "G 1

The Red bull, the Brawn and the Mclaren, have an entrance duct, as per the reg's...and they have a exit duct, there isn't a third port connecting to the internal volume of the diffuser to the ducting... otherwise you would be correct in the operation of pulling air from the lower diffuser.
They are only allowed the entrance ports, that I'm aware off.
Additionally the entrance port is followed by a higher volume area which slows air, not accelerate it....

The double section has its own unique duct opening. That is what was though illegal by the other teams.

http://www.shell.com/home/content/motorsport/ferrari/technical_partnership/f1_explained/diffusers/
The second deck of the diffuser is fed by holes in the floor of the car between the skid block and the reference plane. The regulations state that the floor of the car must have no holes or cut-outs that allow any part of the internal components of the car (sprung mass) to be seen from underneath.
…
BrawnGP’s defence in using their double decker diffuser relied upon the assumption that the skid block and the floor of the car should be considered individually, thereby arguing that the ‘holes’ in the floor were simply gaps in the connecting planes. Ferrari and the other appealing teams, however, took the two planes to be one single surface, rendering the holes illegal.

[quote author="speedsense" date="1256279881

The Red bull, the Brawn and the Mclaren, have an entrance duct, as per the reg's...and they have a exit duct, there isn't a third port connecting to the internal volume of the diffuser to the ducting... otherwise you would be correct in the operation of pulling air from the lower diffuser.
They are only allowed the entrance ports, that I'm aware off.
Additionally the entrance port is followed by a higher volume area which slows air, not accelerate it....

Actually, there is. Look closely at the photograph of the underside of a Red Bull car,



Then at the drawing showing the same view



which points to the ducts that flow into the second "diffuser," which is akin to the red flow chamber in the siphon pump.



This drawing shows how air taken in through the
under-body ductwork is routed over the main diffuser. The end of the separation between the two is shown by a jagged red line.

And the lower drawing in this illustration shows the system in cross-section.



Note how both airflows come from under the car, then are separated, with the upper one coming out just behind the lower. That's what creates and drives the siphon pump.

I beleive the end-view of the Red Bull double diffuser looks something like the Williams or possibly the Brawn.



In Toyota's case, they took a slightly different track, ducting the second "diffuser" duct straight out the back of the car, rather than walling it off and exiting it above, as Brawn and Williams, et al, have done.



The littl winglet you see at the bottom of the Toyota diffuser angles the airflow so that it mixes more completely with the air flowing through the main diffuser, and with that under the wing.

GreyWolf74 - 23 October 2009 02:33 PM

[quote author="speedsense" date="1256279881

The Red bull, the Brawn and the Mclaren, have an entrance duct, as per the reg's...and they have a exit duct, there isn't a third port connecting to the internal volume of the diffuser to the ducting... otherwise you would be correct in the operation of pulling air from the lower diffuser.
They are only allowed the entrance ports, that I'm aware off.
Additionally the entrance port is followed by a higher volume area which slows air, not accelerate it....

Actually, there is. Look closely at the photograph of the underside of a Red Bull car,



Then at the drawing showing the same view



which points to the ducts that flow into the second "diffuser," which is akin to the red flow chamber in the siphon pump.



This drawing shows how air taken in through the
under-body ductwork is routed over the main diffuser. The end of the separation between the two is shown by a jagged red line.

And the lower drawing in this illustration shows the system in cross-section.



Note how both airflows come from under the car, then are separated, with the upper one coming out just behind the lower. That's what creates and drives the siphon pump.

I beleive the end-view of the Red Bull double diffuser looks something like the Williams or possibly the Brawn.



In Toyota's case, they took a slightly different track, ducting the second "diffuser" duct straight out the back of the car, rather than walling it off and exiting it above, as Brawn and Williams, et al, have done.



The littl winglet you see at the bottom of the Toyota diffuser angles the airflow so that it mixes more completely with the air flowing through the main diffuser, and with that under the wing.

Actually you and I are talking the same thing, though the siphon pump, is at the end of the ducting. I was interpeting it as an additional hole in between. My bad...
The vortex generation is what makes this work more effectively, helping channel the air flow out the back for "siphoning"/ accelerated extraction of air, from the lower diffuser. If this what your implying, then we are in agreement as to it's use.
By that, I mean that the siphon you have drawn would end at the "T" intersection.. where the vortices would create "virtual" walls as the continuance of the physical walls that don't exist out the back.
Hope this doesn't sound to confusing....

I think I understand what you mean, Speedsense. It's an interesting use of vortexes as virtual "walls."

Correct me if I'm wrong, but as I recall, another use for an induced vortex is to keep the laminar flow closer to the back half of a wing surface, where it would normally separate. That would help flaps and aelerons to work, among other things.

The more I look at the science of aerodynamics, the more fascinating, nuanced -- and confusing -- it gets. Sometimes, I have to wonder how the pioneers aeronautical and aerodynamic engineering (e.g. the Wright Brothers) ever made sense of it all.