Diffuser stall problem

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bigpat
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Re: Diffuser stall problem

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Interesting topic!

From other responses, and watching the telecast, my opinion is its a combination of pitch (ride height sensitivity), and yaw sensitivity.

The stiff suspension leads me to believe the Williams suffers a bit from pitch or platform sensitivity, needing to try and keep it all as still as possible, but I think it is more a transient turn in issue, where the front wheels are steered, and the car is in yaw.
On Saturday, both drivers binned it on turn in to fast corners, and Kubica's previous comments from his drives has confirmed that is where its lacking. Running the 2017 wing for no better result gives me clue to say it underneath the car, but the whole flow regime under there is so complex. I think the hard part is to find the culprit. It is was apparent in the wind tunnel or through CFD, I'm sure there could make new parts to fix it.

As an aside, Its interesting to see that McLaren have reverted to running lots of Flo Viz on their cars, to try and understand what is clearly a complex problem....

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Big Tea
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Re: Diffuser stall problem

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Would anyone here know please, is there a difference from tyre to tyre?

Possibly the shape or amount of sidewall deformation giving an abbreviated 'C' or 'S' shape and deflecting flow?
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jjn9128
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Re: Diffuser stall problem

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Big Tea wrote:
09 Jul 2018, 12:37
Would anyone here know please, is there a difference from tyre to tyre?

Possibly the shape or amount of sidewall deformation giving an abbreviated 'C' or 'S' shape and deflecting flow?
There will be a small difference in the stiffness of each compound certainly. F1 tyres are handmade so each individual tyre may react slightly differently as well.
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"There is one big friend. It is downforce. And once you have this it’s a big mate and it’s helping a lot." Robert Kubica

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godlameroso
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Re: Diffuser stall problem

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I didn't know they were hand made, that's very interesting. I'm guessing Pirelli has quality control checks to try to ensure an even product for everyone. Although you can never escape odd manufacturing defects here and there, I don't think this is quite the issue for Williams. It becomes an issue when you're fighting for tenths, not seconds behind like Williams was in Silverstone. There's something fundamental on that car that they've completely ignored in it's design, now they're trouble shooting to re-design that part of the car.

As a team owner this has to be the most frustrating thing, because it's still a gamble as to whether it will work or not, and meanwhile you're stuck plum last while making a huge investment to re-build the car. The pressure from share holders, partners, drivers, the way the staff feels having to fight day in day out for the chance of a miracle pay off. Can't imagine having to deal with that, and also knowing the sacrifice has to be made in order for the team to move forward takes a strong mind to deal with that.
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jjn9128
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Re: Diffuser stall problem

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godlameroso wrote:
09 Jul 2018, 14:47
I didn't know they were hand made, that's very interesting. I'm guessing Pirelli has quality control checks to try to ensure an even product for everyone. Although you can never escape odd manufacturing defects here and there, I don't think this is quite the issue for Williams. It becomes an issue when you're fighting for tenths, not seconds behind like Williams was in Silverstone. There's something fundamental on that car that they've completely ignored in it's design, now they're trouble shooting to re-design that part of the car.

As a team owner this has to be the most frustrating thing, because it's still a gamble as to whether it will work or not, and meanwhile you're stuck plum last while making a huge investment to re-build the car. The pressure from share holders, partners, drivers, the way the staff feels having to fight day in day out for the chance of a miracle pay off. Can't imagine having to deal with that, and also knowing the sacrifice has to be made in order for the team to move forward takes a strong mind to deal with that.
There are automated parts of the process - so they're hand made in the same way as F1 cars are hand made. But there is a person putting the rubber onto the tread...etc. There will be QC checks as in any industry - measurements of everything to show they meet standards then destructive testing and disassembly of a prescribed number of tyres from each batch.


A fundamental issue like diffuser instability is worth investing in trying to overcome- if only to prevent the next car suffering from the same issue. They've sacked the head of aero so the new head will have a different philosophy on the car and you want to be sure the wind tunnel and CFD will be giving the correct answers.
#aerogandalf
"There is one big friend. It is downforce. And once you have this it’s a big mate and it’s helping a lot." Robert Kubica

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godlameroso
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Re: Diffuser stall problem

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jjn9128 wrote:
09 Jul 2018, 15:00
godlameroso wrote:
09 Jul 2018, 14:47
I didn't know they were hand made, that's very interesting. I'm guessing Pirelli has quality control checks to try to ensure an even product for everyone. Although you can never escape odd manufacturing defects here and there, I don't think this is quite the issue for Williams. It becomes an issue when you're fighting for tenths, not seconds behind like Williams was in Silverstone. There's something fundamental on that car that they've completely ignored in it's design, now they're trouble shooting to re-design that part of the car.

As a team owner this has to be the most frustrating thing, because it's still a gamble as to whether it will work or not, and meanwhile you're stuck plum last while making a huge investment to re-build the car. The pressure from share holders, partners, drivers, the way the staff feels having to fight day in day out for the chance of a miracle pay off. Can't imagine having to deal with that, and also knowing the sacrifice has to be made in order for the team to move forward takes a strong mind to deal with that.
There are automated parts of the process - so they're hand made in the same way as F1 cars are hand made. But there is a person putting the rubber onto the tread...etc. There will be QC checks as in any industry - measurements of everything to show they meet standards then destructive testing and disassembly of a prescribed number of tyres from each batch.
https://www.youtube.com/watch?v=qG3sdF8IXyA

A fundamental issue like diffuser instability is worth investing in trying to overcome- if only to prevent the next car suffering from the same issue. They've sacked the head of aero so the new head will have a different philosophy on the car and you want to be sure the wind tunnel and CFD will be giving the correct answers.
Good point, perhaps the area to be worked on won't change much for next year anyway. Ultimately they still have the same diffuser, the same bargeboards, although not as tall, and largely similarly functioning front wing. It's definitely going to shake things up at the start of the season though because I imagine a fair amount of tuning will be involved which could be worth several tenths just through setup changes alone.
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Vanja #66
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Re: Diffuser stall problem

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roon wrote:
08 Jul 2018, 21:51
The image illustrates the point being made. FIA unable to alter laws of physics, yet. Current cars' VGs at the floor leading edge and bargeboard footplate to me suggest that they are employing multiple smaller vortices stacked side-by-side beneath the floor. Can't cram a large vortex into a small gap with out losing its rotation.
It's my belief teams started with that philosophy last year, but now most of them have one single large floor-like VG (or 2-3 to enhance the effect, but a single trailing edge) that produces 1 strong vortex running along the trailing edge, like Ferrari did from the start of the 2017 season. This is used to seal the floor area behind barge boards, thus leaving mostly clean air running from under the nose (and it's sides) to the floor and preventing any front tyre wake to enter the floor and diffuser.

Take a look at these (by variante):

Image

Image

Air is turning down very, very aggressively on vertical barge board pieces, on a relatively undeveloped car. If it's doing so, it's way more effective to shape your bodywork to suit natural flow, than to make it do what you want and put too much horizontal wings (like most teams did in early 2017).

Image

Look at what a great match Ferrari lower barge board wings makes with variante's simulation streamlines.

And it all looks very much like standard floor-edge VG:

Image

Keep in mind that tee-tray is shorter from last year, so there is very little room from ground to lowest barge board elements and very easy to seal-up.
And they call it a stall. A STALL!

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Big Tea
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Re: Diffuser stall problem

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jjn9128 wrote:
09 Jul 2018, 13:15
Big Tea wrote:
09 Jul 2018, 12:37
Would anyone here know please, is there a difference from tyre to tyre?

Possibly the shape or amount of sidewall deformation giving an abbreviated 'C' or 'S' shape and deflecting flow?
There will be a small difference in the stiffness of each compound certainly. F1 tyres are handmade so each individual tyre may react slightly differently as well.
So how much difference in ground clearance (at the plank) do you think this may make? #Enough to disturb the seal of air and lose downforce?
I know none of them have much suspension movement but the Williams seems to 'bounce on the tyres' sometimes.
Would this spill the air and case the back end to break away?
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jjn9128
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Re: Diffuser stall problem

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Big Tea wrote:
09 Jul 2018, 16:31
So how much difference in ground clearance (at the plank) do you think this may make? #Enough to disturb the seal of air and lose downforce?
I know none of them have much suspension movement but the Williams seems to 'bounce on the tyres' sometimes.
Would this spill the air and case the back end to break away?
Without getting a Pirelli tyre on a rolling road under load it's impossible to say. Tyre pressure will be a bigger difference I would think though.
#aerogandalf
"There is one big friend. It is downforce. And once you have this it’s a big mate and it’s helping a lot." Robert Kubica

bigpat
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Re: Diffuser stall problem

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Pirelli supply all teams with wind tunnel model tyres, that mimic the full size characteristics, including deflection in yaw, which all the wind tunnels can do, and sidewall flex can be modelled in CFD as well. The teams will always want to run the lowest tyre pressure possible more best grip. There are now nominated minimum pressures anyhow.

Having all the flows re-attach in a consistent manner after disturbance would be a big issue with the current car. The harder you try to work the air, the less tolerant it is as well....