Red Bull RB18

[GioKer32]

Experience and knowledge leave you with educated guesses, which can be a real benefit actually... Speeds things up quite a lot, adds value and yields good hourly rates. For instance, when I said this

What RB did is very different, they emphasized the curvature around diffuser kink (mandated by rules) and they opened up the diffuser side wall to let the air from the top of the floor enter there to feed and energize the vortex. This makes the floor work more like classical flat-floor with diffuser, as it doesn't rely on ground proximity for optimal performance. Energizing the vortex reduces the pressure in diffuser, which in turn also drives the front of the floor and reduces overall pressure under the floor.

https://i.ibb.co/2dWCbvp/iBwWx4U.jpg

This is just a general outline of their floor philosophy. This is why RB never had any problems with bouncing, but why they also lacked overall downforce compared to Ferrari.

I didn't guess out of my rear, I know which geometries are at play and how those influence floor design in practice. Like this quick floor profile CFD demonstrates:

https://i.ibb.co/44dsV89/rb-floor.jpg

RB floor is by far the most complex out there, it uses a lot of additional features to negate the pressure increase that comes with greater tunnel height (not decrease, as you seem to think), including tub profile, vanes, lots of small geometry changes etc. They made a very small throat height and created a strong, but quite small downforce area around it. Only they know how the rest of the floor pressure distribution looks like, especially at the front where all the fun geometry is. Take a look at this thread to see a glimpse of how inconsistent the pressure distribution at the front is:

viewtopic.php?p=879079#p879079

This is very far from what typical ground effect floor pressure distribution looks like and the rear end is practically the same as previous generation diffuser floors. You can be sure that other teams, with conventional ground effect floor design, have a very, very different pressure distribution, far more even as opposed to RB peaky downforce design.

Seeing how strongly this design will be affected by increasing floor throat and edge height in 2023, I can understand why Horner was so much against it. Other than the change playing right to Mercedes' hand...

I appreciate this analysis so much!
On top of that, I'd like You to answer a question that I thought of while reading the post: do you believe that this design philosophy by RB is the reason for their outstanding straight-line speed? Maybe the diffuser kink is shaped in a way that allows the diffuser to stall at very high speeds.

[ringo]

We would need a more accurate model of the floor to draw conclusions.
As well as a comparison between a typical floor of the other cars to say for sure what is happening with the RB18.
That comparison must also have different floor heights at different speeds.
Its best to look at what part of the tracks and what speed regime the rb18 is vastly superior to the others.
But as much as we talk about the floor, the suspension movement is optimizing the floor.
What is evident is the car has very low drag on the straights. They may have adopted a mercedes rear suspsension trick into a new trick. The devil is in the detail. If i get the time i could try to model it, but the modeling will take a lot of effort and time that i dont have right now.

[Vanja #66]

I appreciate this analysis so much!
On top of that, I'd like You to answer a question that I thought of while reading the post: do you believe that this design philosophy by RB is the reason for their outstanding straight-line speed? Maybe the diffuser kink is shaped in a way that allows the diffuser to stall at very high speeds.

No, to be honest, I don't think low drag has that much to do with floor drag. Yes, diffusers are now quite tall and have a big rearward projection, but floors are still elements with lowest drag on the car. Sidepods are very slippery, very streamlined and they work well with the floor. Rear wing design is the reason behind the most of RB top speed performance, with big DRS flaps from the first race. Without DRS, RB top speed is always mostly the same as Ferrari for instance.

I don't know why people have this idea that you can stall a diffuser at higher speeds and this would bring some benefit. With higher speed, there is more energy "in air", Reynolds number is higher and it's actually much harder to experience separation. Also, with these cars, when floor and diffuser stall due to choking, the car starts bouncing - the same thing would happen if diffuser would somehow stall without choking.

[ringo]

Yes it's harder to experience separation at higher speeds.
But depends on the geometry you can cause separation by changing the angle of that shape against that higher momentum air. The air wont follow the surface of the geometry as it would at a lower speed.
As for the bouncing i do not know enough about that to comment on, but that's where the mystery of the suspension comes in.
But agree with you on the low drag. But if there is less dependence on wing downforce and thus less drag from the wings compared to the other cars, the rb18 would be inherently less draggy.

[FDD]

I appreciate this analysis so much!
On top of that, I'd like You to answer a question that I thought of while reading the post: do you believe that this design philosophy by RB is the reason for their outstanding straight-line speed? Maybe the diffuser kink is shaped in a way that allows the diffuser to stall at very high speeds.

No, to be honest, I don't think low drag has that much to do with floor drag. Yes, diffusers are now quite tall and have a big rearward projection, but floors are still elements with lowest drag on the car. Sidepods are very slippery, very streamlined and they work well with the floor. Rear wing design is the reason behind the most of RB top speed performance, with big DRS flaps from the first race. Without DRS, RB top speed is always mostly the same as Ferrari for instance.

I don't know why people have this idea that you can stall a diffuser at higher speeds and this would bring some benefit. With higher speed, there is more energy "in air", Reynolds number is higher and it's actually much harder to experience separation. Also, with these cars, when floor and diffuser stall due to choking, the car starts bouncing - the same thing would happen if diffuser would somehow stall without choking.

If the diffuser is stalled, does this mean that drag is higher?
Since that uncontrolled vortices are generated, probably, I do not know, I'm asking.

[Vanja #66]

But agree with you on the low drag. But if there is less dependence on wing downforce and thus less drag from the wings compared to the other cars, the rb18 would be inherently less draggy.

Yes, agreed. RB18 has better aero efficiency, albeit slightly downforce-limited, before td39 at least.

If the diffuser is stalled, does this mean that drag is higher?
Since that uncontrolled vortices are generated, probably, I do not know, I'm asking.

It could also mean higher drag, yes, no doubt. Also, uncontrolled vortices are usually called eddies

[101FlyingDutchman]

But agree with you on the low drag. But if there is less dependence on wing downforce and thus less drag from the wings compared to the other cars, the rb18 would be inherently less draggy.

Yes, agreed. RB18 has better aero efficiency, albeit slightly downforce-limited, before td39 at least.

If the diffuser is stalled, does this mean that drag is higher?
Since that uncontrolled vortices are generated, probably, I do not know, I'm asking.

It could also mean higher drag, yes, no doubt. Also, uncontrolled vortices are usually called eddies

Or laminar flow separation in airliner terms

[Zynerji]

Why did the 93 Williams have a button to "pop up" the diffuser on the straights?

[aleks_ader]

Pop up could also works in connection with stalled beamwing or even RW. Still i dont know for sure. Its mine huge speculation. Also consequently front spliter in closer to the ground. Witch could choke front intakes of floors. Choking surely increase drag i think.

Furthermore i imagine less energy trough undersides could choke beamwing extraction and colapse RW flow to stall whole sys as a whole. Maybe u gain some drag with floor that way but u overcome rest of it via with beamwing and RW.

[aleks_ader]

Ofc Williams could have pop down and effect also. Depends of geometry really. At end of day i got no data to prove any of it. We can just assume RB floor is quite differentiator from rest of grid. And results shows its strengths and weakness.

[AR3-GP]

I appreciate this analysis so much!
On top of that, I'd like You to answer a question that I thought of while reading the post: do you believe that this design philosophy by RB is the reason for their outstanding straight-line speed? Maybe the diffuser kink is shaped in a way that allows the diffuser to stall at very high speeds.

No, to be honest, I don't think low drag has that much to do with floor drag. Yes, diffusers are now quite tall and have a big rearward projection, but floors are still elements with lowest drag on the car. Sidepods are very slippery, very streamlined and they work well with the floor. Rear wing design is the reason behind the most of RB top speed performance, with big DRS flaps from the first race. Without DRS, RB top speed is always mostly the same as Ferrari for instance.

I don't know why people have this idea that you can stall a diffuser at higher speeds and this would bring some benefit. With higher speed, there is more energy "in air", Reynolds number is higher and it's actually much harder to experience separation. Also, with these cars, when floor and diffuser stall due to choking, the car starts bouncing - the same thing would happen if diffuser would somehow stall without choking.

@Vanja #66.

I think it's a bit more complicated than this. We've seen many teams trial larger rear flaps including Ferrari and never seem to generate such a pronounced reduction in drag when DRS is opened. If it was so simply, everybody would have implemented it already seeing as it would allow you to have downforce in the corners and then no penalty on the straights in qualifying. As of yet, we've not seen that trend...

I do believe Red Bull have replicated some kind of diffuser stalling system. You say the floor doesn't cause drag, but it does. The floor has turning vanes at the front. Those introduce flow losses. The floor and diffuser have aggressive volume expansions which introduce losses. The skin friction of the entire floor introduces losses. The floor edge itself is a source of losses which increase as the floor power increases.

If you were to kill the the diffuser, you would depower the entire floor. Velocity everywhere is reduced. The losses due to boundary layers, expansions, and turning vanes are reduced are they not? You suggested previously that the RB18 philosophy is that of a flat floor race car w/ a diffuser accelerating the air over flat floor. Using the diffuser to power the floor. Is this not the clue as to the behavior of the car and why stalling the diffuser would reduce drag?

This mechanism was described as the trick for Mercedes last season as well. RB seem to be using the DRS as the on off switch whereas last season Mercedes had to faff about with minimum cornering speeds to tune their system properly (it's like the W13 system targeted the non-DRS straights whereas RB's system targets the DRS straights).

Red Bull would be able to predict the ride height and pitch angle of the car given the fixed front wing load, and the on-off loads of the rear wing at high speed. As you say, the RB18 only exhibits this jet mode when the DRS is open. When the DRS is closed, Ferrari matches them in the straights.

[Sieper]

Isn’t the Mercedes W13 drag from more airflow hitting the rear wheel? They have the sidepod out of the way, thus the most air flowing undisturbed onto the rear wing, but also, against the rear wheel. More ultimate DF than RB18 but also more drag.

[Just_a_fan]

Isn’t the Mercedes W13 drag from more airflow hitting the rear wheel? They have the sidepod out of the way, thus the most air flowing undisturbed onto the rear wing, but also, against the rear wheel. More ultimate DF than RB18 but also more drag.

That's the idea postulated right at the beginning of the season using the original Barcelona test version. The later car probably generates drag from the large downwash device supporting the mirrors.

All open wheel cars have air smacking in to the tyres - both front and rear. It's the single largest creator of drag on the cars after the rear wing.

[AR3-GP]

We'll probably get yelled at for going off topic , but it's not obvious to me that the RB18 is much different to other cars when the DRS is closed. We saw this in Australia. It's the DRS open configuration that deserves a fair bit of understanding as that is what really differentiates it from it's rivals. I've contemplated trivial things like the size of the DRS flap, but if it was that simple, other teams would have caught on.

[ringo]

I am not so sold on the wider pods and rear wheel drag reduction idea. The sidepods dont project outward enough to seem to have an influence on the air hitting the rear tyres.
I would like to see a CFD study with some numbers on this for me to be comfortable accepting it.
The claim is the sidepod manipulate the front wheel wake to reduce drag. But i think they are too far downstream of the front wheels to have much influence. The frong wheels have a low pressure are behind them, with a lot of eddies and turbulence. In the older formula the barge boards would push the air flowing along the fuselage and underneath it to the side, which would indirectly pull along the messy air behind the front wheel. If this is to improve flow to and around the sidepods itself I am not sure.
But to say the wider pods which are even furth from the front wheels are reducing drag on the rears..it would need to be demonstrated.