Aerodynamics of Porpoising

[Sevach]

Wonder if he means steady state deflection negatively changing the floor shape, or flutter at the floor extremities. Or both.

The article is about him complaing that floor stays worked against Alpine (their car is heavier and stiff enough already, while others have lighter cars in need of stiffening), so flutter must be a part of it imo.

[ispano6]

The big diffuser and edge wing like on the Mercedes with no sidepods to share the load, means the floor has more load to take than something like a Ferrari, or Alpine. That means the floor is more prone to deformation and flexing. More deformation and flexing means more vortex shedding unless you make the floor stronger. If you make it stronger then it's also heavier.

This post got a pair of downvotes. Laughs in engineer

It reminds me of speedboat porpoising.

"Porpoising is the result of the motor’s outdrive pushing the boat upwards, essentially boosting it out of the water – albeit for a short period of time. Once the boat comes back down, the outdrive will once again push it back out of the water. This cycle will continue to repeat until either the boat’s speed is reduced or the trim is fixed."

Mercedes had to resort to using the stays to keep the floor from flexing down (could this cause lift due to the angle?). They also had to trim rear-wing down force. Teams that don't need the stays have much stronger(but possibly heavier) floors. As always all teams aim to strike a balance between straight-line speed and down force. I found the RedBull Rb18 underbody and floor particularly interesting as it reminded me of the keel of a large boat as well as the underbody of a speedboat/yacht.

[godlameroso]

The big diffuser and edge wing like on the Mercedes with no sidepods to share the load, means the floor has more load to take than something like a Ferrari, or Alpine. That means the floor is more prone to deformation and flexing. More deformation and flexing means more vortex shedding unless you make the floor stronger. If you make it stronger then it's also heavier.

This post got a pair of downvotes. Laughs in engineer

It reminds me of speedboat porpoising.

"Porpoising is the result of the motor’s outdrive pushing the boat upwards, essentially boosting it out of the water – albeit for a short period of time. Once the boat comes back down, the outdrive will once again push it back out of the water. This cycle will continue to repeat until either the boat’s speed is reduced or the trim is fixed."

Mercedes had to resort to using the stays to keep the floor from flexing down (could this cause lift due to the angle?). They also had to trim rear-wing down force. Teams that don't need the stays have much stronger(but possibly heavier) floors. As always all teams aim to strike a balance between straight-line speed and down force. I found the RedBull Rb18 underbody and floor particularly interesting as it reminded me of the keel of a large boat as well as the underbody of a speedboat/yacht.

Funnily enough the way boats fix porpoising is adding a flat stay at the rear of the boat.

[cheeRS]

The big diffuser and edge wing like on the Mercedes with no sidepods to share the load, means the floor has more load to take than something like a Ferrari, or Alpine. That means the floor is more prone to deformation and flexing. More deformation and flexing means more vortex shedding unless you make the floor stronger. If you make it stronger then it's also heavier.

This post got a pair of downvotes. Laughs in engineer

It reminds me of speedboat porpoising.

"Porpoising is the result of the motor’s outdrive pushing the boat upwards, essentially boosting it out of the water – albeit for a short period of time. Once the boat comes back down, the outdrive will once again push it back out of the water. This cycle will continue to repeat until either the boat’s speed is reduced or the trim is fixed."

Mercedes had to resort to using the stays to keep the floor from flexing down (could this cause lift due to the angle?). They also had to trim rear-wing down force. Teams that don't need the stays have much stronger(but possibly heavier) floors. As always all teams aim to strike a balance between straight-line speed and down force. I found the RedBull Rb18 underbody and floor particularly interesting as it reminded me of the keel of a large boat as well as the underbody of a speedboat/yacht.

Newey has been working on America's Cup boats since ~2014 so it wouldn't surprise me if he's learned even more tricks, concepts, and methods that he's applying directly to the RB16. The guy is inimitable. And he's left handed, so I feel like we're buddies, kind of

https://en.wikipedia.org/wiki/INEOS_Britannia

[saviour stivala]

In the past days of ground-effect cars there were only two ways to get over any porpoising problems that showed-up. One was by restricting the venture inlet, and the other by expanding its outlet. The problem was that by doing any of the above some down-force would have to be left behind. But the question is. Why do they do any one of the above to minimize their porpoising problems?. It might be either that it is not easy with the car as designed, or that budget/development restrictions nd or whole car as designed somehow restricts any of those possibilities.

[atanatizante]

Could someone please explain if porpoising is influenced by the car`s mass distribution, by the centre of pressure, by the centre of gravity or a combination of all 3 and maybe much more factors than those above mentioned ... Thanks in advance!

[godlameroso]

In the past days of ground-effect cars there were only two ways to get over any porpoising problems that showed-up. One was by restricting the venture inlet, and the other by expanding its outlet. The problem was that by doing any of the above some down-force would have to be left behind. But the question is. Why do they do any one of the above to minimize their porpoising problems?. It might be either that it is not easy with the car as designed, or that budget/development restrictions nd or whole car as designed somehow restricts any of those possibilities.

Sound pressure wave induced buffeting? You lessen the pressure waves when you reduce the difference in flow velocity from the throat to the outlet/diffuser. If the diffuser is at nearly atmospheric pressure and has low velocity flow, the high velocity jet impinging on it creates pressure waves, which can cause flow separation/reversal. So by reducing flow velocity, you lower downforce, but you also lower the transition separation.

In rocketry, you avoid this issue by reducing the backpressure of the outlet/diffuser of your nozzle. In F1 the beam wing and the edge wing are used to reduce the back pressure in the diffuser. The beam wing's energized flow entrains air exiting the diffuser lowering it's back pressure. Ferrari and Red Bull currently have the best beam wings. Not only do they upwash, but they outwash as well, Mercedes is close behind in their up/outwashing beam wing.

The edge wing can channel high speed air into the diffuser that will further reduce back pressure. Anything you can do to shove more air into and out of the diffuser will reduce the back pressure in the diffuser, and lower the velocity transition, as you'll increase the velocity everywhere in the tunnel/floor.



Red Bull nozzles air directly into the diffuser with their edge wing. Notice how smooth and rounded the mouse hole on the side of the diffuser is on the RB18 vs how tall and well rounded on the W13.



According to this video @ 1:15


You see that perhaps the mouse hole opening on the Mercedes may be contributing to their flow instability. Whereas the RB18 has a much smoother more elliptical shape, which is less prone to such flow instabilites.

[Bandit1216]

I'm wondering: All speculation and impossible to science (not by me at least) but:

What I see now is a car with relatively huge sidepods (Ferrari) that is right up there. I did not foresee that. While an other one with very small sidepods is struggling.

I have a feeling it's a bit like the rake discussion all over. Low and long being worse in theory, yet far better to control and predict, and thus winning (Merc). With that regards I always found it strange most (not all) seemed to copy RB and not the winning merc. (2014 -2019)

The same now with the sidepods. The Ferrari to me looks like they chose for less downforce from the floor and more from above the floor. Imo a worse solution by gut feeling, yet they prevail because they can predict far better. McL also having a quite big sidepod but can't seem to benefit the same as Ferrari, proofing its not all that easy.

And then the same goes for the route one takes with the intake channels to the floor. To me it looks like one can choose to take more air out of that inlet area to seal the floor yet less to use for the high speed, low pressure that creates the actual downforce under the car. RB opting for more sealing and less downforce. McL also opting for more sealing yet the combination with their sidepods seems to not work.

So my not so scientific theory:

Ferrari chose more above floor and less under floor downforce, yet the part that they do use under the floor, they mostly use for downforce and not sealing. The huge sidepods doing the sealing job and the bathtub part doing what the b-wing does on the RB. In the process creating a Monaco winning car

McL seems to me looks like they have the huge sidepods doing the sealing, yet also the channels set up for sealing as well losing the total downforce in the process.

RB opting for not very small yet huge undercut sidepods using quite a lot of sidepod in combination with huge B wing for upper body downforce, the floor setup for more sealing. So albeit a different approach as Ferrari, yet working quite well. RB creating a monza killer in the process. I predict Charles winning his home GP. That's new!

Merc then chose for underfloor downforce and almost no sidepods, setting the floor up for downforce relative more and less for sealing as well and thus in the process creating an car that is very fast in theory, yet having the most problems getting the performance. (I bit like a high rake RB that seems a nightmare to setup and drive, but very fast, (sometimes))

AT, AR, and Haas getting it relatively right in above combinations and Williams and AM getting it wrong. Alpine staying about where they are.

Proof me wrong please!

[vorticism]

Porpoising is still visible in 2023 (see Ferrari in Jeddah). As before it is seen mainly on the straights where downforce is highest. The increase in downforce with speed correlates with porpoising; and generally peak downforce is not needed on the straights except for braking. If floor downforce could be shed then porpoising might be mitigated.

Proposal for diffuser DRS: move the DRS mechanism from the rear wing to the diffuser. This already exists in the Aston Martin Valkyrie (as confirmed in press articles this year).

Looks to have movable doors in the tunnel roofs. May be for additional cooling at standstill or a form of DRS.

[AR3-GP]

Porpoising is still visible in 2023 (see Ferrari in Jeddah). As before it is seen mainly on the straights where downforce is highest. The increase in downforce with speed correlates with porpoising; and generally peak downforce is not needed on the straights except for braking. If floor downforce could be shed then porpoising might be mitigated.

Proposal for diffuser DRS: move the DRS mechanism from the rear wing to the diffuser. This already exists in the Aston Martin Valkyrie (as confirmed in press articles this year).

Looks to have movable doors in the tunnel roofs. May be for additional cooling at standstill or a form of DRS.
https://i.imgur.com/j1bA4Is.jpg

The drag reduction from stalling the difffuser would be much weaker than opening the rear wing. Why not just mandate a smaller DRS slot opening distance?

Also, raising a flap inside the diffuser tunnel would effectively be a "speed brake".

[vorticism]

The drag reduction from stalling the difffuser would be much weaker than opening the rear wing. Why not just mandate a smaller DRS slot opening distance?

Also, raising a flap inside the diffuser tunnel would effectively be a "speed brake".

Floor produces the most downforce although more efficiently. So it might be close. Anyone know the ballpark numbers?

Stall can lower the drag without adding drag; that's how the F-duct worked.