MOD EDIT: Split from this thread here - felt that it should kinda be split out into it's own thing
I wanted to bump this thread up and hear if Jin and Vyssion can comment on vortex shedding and aero elasticity and whether they can induce porpoising issues, especially in regards to the entire duct height being set by a sprung suspension with its own resonances.
Particular, honing in on this:
I'm going to try... aerodynamics are not steady state, nice smooth contour plots in CFD and wind tunnel results are the result of long time averaging intervals. In reality the trailing edge flow will be as Vyssion showed 2 posts back - more akin to a Karman vortex street. Wing's are also not infinitely stiff so this may result in some oscillations which will affect pressure distribution - which will cause the wing to pitch and heave - but the oscillatory forces are rather small so it's unlikely to create very big deflections. However if you watched the Haas sharkfin and T-wing last year you'll see those unsteady effects can get quite big - even to the extent that parts fail because of it.
Especially in regards to how the underbody venturi represents a much larger share of the downforce, so the oscillations may have enough magnitude to induce the porpoising.
I wanted to bump this thread up and hear if Jin and Vyssion can comment on vortex shedding and aero elasticity and whether they can induce porpoising issues, especially in regards to the entire duct height being set by a sprung suspension with its own resonances.
Particular, honing in on this:
I'm going to try... aerodynamics are not steady state, nice smooth contour plots in CFD and wind tunnel results are the result of long time averaging intervals. In reality the trailing edge flow will be as Vyssion showed 2 posts back - more akin to a Karman vortex street. Wing's are also not infinitely stiff so this may result in some oscillations which will affect pressure distribution - which will cause the wing to pitch and heave - but the oscillatory forces are rather small so it's unlikely to create very big deflections. However if you watched the Haas sharkfin and T-wing last year you'll see those unsteady effects can get quite big - even to the extent that parts fail because of it.
Especially in regards to how the underbody venturi represents a much larger share of the downforce, so the oscillations may have enough magnitude to induce the porpoising.
Personally, I think that the porpoising is less an aero-elastic effect, and more a sort of "heaving wing" effect that's not being damped out by the suspension... My quick and dirty take on it would be that the suction under the cars contributes to so much more of the overall car's downforce this year, and so given the shift towards a more floor-downforce-proportioned car in general, the coupling of those two things means that the pressure drop under the car (which is always much larger relative to ambient than the pressure side of any aerodynamic surface) has caught out some teams in terms of the aerodynamic damping required to stop a "heaving wing" dynamic from occuring.
It's kind of like how a dutch roll flight mode gets started... a gust on one wing increases local velocity, which increases lift, which increases lift-induced-drag, and so pulls the wing upward and aftward... because that wing is mechanically coupled to the fuselage, and then the other wing, the opposing wing then moves forward through the air via that connection, which then is moving faster vs. freestream, so it too then increases in lift, which increases lift-induced-drag, and so that wing pulls upward and aftward... whilst that motion is happening, as the wing moves backward, it's relative velocity drops even more, and so the reduction in lift + lift-induced-drag etc etc is magnified... keep that process going, and don't damp it out with your control surfaces, and you sort of "waddle" using your wingtips through the sky, until the oscillations get so bad that you are forced into a spiral mode, which is much harder to recover from, and then you crash.
It's kind of the same kind of "process" going on, but in relation to motorsport, that you see in a heaving wing flow... For some reason, the video I was hoping to find proved a little harder than I thought... but this kind of shows what I'm on about:
As downforce increases, the wing (or floor) is pulled closer to the ground, venturi / bernoulli magic happens ofc, downforce increases, but to a point... whatever that point is (driver command, choking the inlet to the floor, curb, small squirrel or something, idk), downforce reduces, and then the wing (floor) rises back up under the suspension reaction forces until the "issue" stops occuring... then the floor starts to work correctly, and the process repeats.
I'm not a suspension expert, but given how "fast" the porpoising up-down shaking appears to be going, it kinda feels like the cars are just bouncing on and off the springs, without the velocity damping (from the aptly named dampers) that would reduce the speed of that up-down motion... slow that bounce speed enough, through damping, and you could prevent that shaking, I would have assumed... Now, whether that damping is coming from some weird interaction of tyres + suspension + deflection in chassis or idk... some other complicated combination, I'm not sure, but that's just my take on what's going on... the cars are really stiffly sprung so a fast rebound like that isn't something I'd be surprised by.
If it didn't affect multiple cars in the year, I'd almost be tempted to wonder whether it was some resonance issue (either mechanical, aerodynamic, or both) that was occuring... similar to the tyre sidewall resonances we saw explode them a couple years back... but given how different each car is this year... ehhhh....
Maybe a case to bring back inertial dampers...........
Re: Aerodynamics of Porpoising
Posted: 01 Apr 2022, 07:16
by Stu
Thank you Vyssion!
That monster post shows how potentially complex the situation could be. And how there really may be no quick fix for it.
The biggest shame is that they will likely never tell us what their particular fix is! Despite the show-and-tell…..
Re: Aerodynamics of Porpoising
Posted: 01 Apr 2022, 13:46
by Stu
Using the W13 as an example (because that appears to be the most violently affected), could their radiator/cooling package be restricting what they can do to cure the issue (aerodynamically)?
Looking at some of the photos of their packaging the lowest point of the cooling kit is below the height of the Lower SIS. This looks to put a very defined upper limit on the size of throat that they can use, it is also located very specifically in relation to the axles.
Re: Aerodynamics of Porpoising
Posted: 01 Apr 2022, 14:37
by PhillipM
I don't think you'd be able to run that much low speed damping without massively upsetting the mechanical balance of the car or shifting most of the vibration/bounce to the tyrewalls anyway, it's one you wanted a mass damper or a serious pitch inerter for but.... well they banned those.
Re: Aerodynamics of Porpoising
Posted: 02 Apr 2022, 17:40
by Oehrly
I just came across this explanation of porpoising by Peter Wright on YouTube:
The explanation seems to be pretty similar to what Vyssion wrote above. A very interesting topic overall!
I just came across this explanation of porpoising by Peter Wright on YouTube:
The explanation seems to be pretty similar to what Vyssion wrote above. A very interesting topic overall!
As Peter Wright was one of key people introducing ground effect cars, this is very interesting. I think its a big advantage to have an engineer in your team withexperience and knowledge in that regard. I remember Ross Brawn saying that porpoising is just about physics and engineers like himself, Pat Symonds etc. they all have experienced porpoising early in their careers and know exactly where it comes from and how to cure it, while the younger engineers seem to be a little wet behind their ears in that regard. Whats interesting i think is that the teams who are suffering less from porpoising or were able to solve it quickly, they all have an experienced engineer like that among their ranks. Red Bull has Newey who gained experience with ground-effect cars in the Indy-Car Series, Ferrari has their adviser Rory Byrne who designed ground-effect cars in the early 80's, McLaren(slow, but no porpoising)has Neil Oatley who helped designing ground effect cars in the early 80's, Alfa has Willem Toet who gained experience with cars like that in the first years of his career and Haas is probably benefitting from Ferraris and Rory Byrnes knowledge. Mercedes, Williams and Aston Martin, who are suffering most from porpoising in my opinion, do not have an engineer like that in their team. I think this is also an explaination why some teams have problems with solving their porpoising-issue while others were able to solve it quickly.
I just came across this explanation of porpoising by Peter Wright on YouTube:
The explanation seems to be pretty similar to what Vyssion wrote above. A very interesting topic overall!
As Peter Wright was one of key people introducing ground effect cars, this is very interesting. I think its a big advantage to have an engineer in your team withexperience and knowledge in that regard. I remember Ross Brawn saying that porpoising is just about physics and engineers like himself, Pat Symonds etc. they all have experienced porpoising early in their careers and know exactly where it comes from and how to cure it, while the younger engineers seem to be a little wet behind their ears in that regard. Whats interesting i think is that the teams who are suffering less from porpoising or were able to solve it quickly, they all have an experienced engineer like that among their ranks. Red Bull has Newey who gained experience with ground-effect cars in the Indy-Car Series, Ferrari has their adviser Rory Byrne who designed ground-effect cars in the early 80's, McLaren(slow, but no porpoising)has Neil Oatley who helped designing ground effect cars in the early 80's, Alfa has Willem Toet who gained experience with cars like that in the first years of his career and Haas is probably benefitting from Ferraris and Rory Byrnes knowledge. Mercedes, Williams and Aston Martin, who are suffering most from porpoising in my opinion, do not have an engineer like that in their team. I think this is also an explaination why some teams have problems with solving their porpoising-issue while others were able to solve it quickly.
I’m ready to be shot down in flames for this, but….
Back in the (good?) old days, there were A LOT of race-car constructors as ALL race series were open. Each of these constructors had designers and engineers that used a combination of their knowledge & experience to continually build better cars in competitive environments - literally “win on Sunday, sell on Monday”!
Some of best of these designers/engineers eventually moved into F1 via a multitude of categories (particularly if they spent time at places like Lola, March, Reynard & others), thereby picking up a great deal of experience.
Nowadays engineers tend to aim straight for F1 from academia, partly because the number of open race series and race car constructors has reduced massively (due to spec or limited competition series), so they do not bring that experience with them. To compound that, the engineering departments in F1 teams are now so vast that they have to specialise, which further compounds the issue.
I just came across this explanation of porpoising by Peter Wright on YouTube:
The explanation seems to be pretty similar to what Vyssion wrote above. A very interesting topic overall!
As Peter Wright was one of key people introducing ground effect cars, this is very interesting. I think its a big advantage to have an engineer in your team withexperience and knowledge in that regard. I remember Ross Brawn saying that porpoising is just about physics and engineers like himself, Pat Symonds etc. they all have experienced porpoising early in their careers and know exactly where it comes from and how to cure it, while the younger engineers seem to be a little wet behind their ears in that regard. Whats interesting i think is that the teams who are suffering less from porpoising or were able to solve it quickly, they all have an experienced engineer like that among their ranks. Red Bull has Newey who gained experience with ground-effect cars in the Indy-Car Series, Ferrari has their adviser Rory Byrne who designed ground-effect cars in the early 80's, McLaren(slow, but no porpoising)has Neil Oatley who helped designing ground effect cars in the early 80's, Alfa has Willem Toet who gained experience with cars like that in the first years of his career and Haas is probably benefitting from Ferraris and Rory Byrnes knowledge. Mercedes, Williams and Aston Martin, who are suffering most from porpoising in my opinion, do not have an engineer like that in their team. I think this is also an explaination why some teams have problems with solving their porpoising-issue while others were able to solve it quickly.
I’m ready to be shot down in flames for this, but….
Back in the (good?) old days, there were A LOT of race-car constructors as ALL race series were open. Each of these constructors had designers and engineers that used a combination of their knowledge & experience to continually build better cars in competitive environments - literally “win on Sunday, sell on Monday”!
Some of best of these designers/engineers eventually moved into F1 via a multitude of categories (particularly if they spent time at places like Lola, March, Reynard & others), thereby picking up a great deal of experience.
Nowadays engineers tend to aim straight for F1 from academia, partly because the number of open race series and race car constructors has reduced massively (due to spec or limited competition series), so they do not bring that experience with them. To compound that, the engineering departments in F1 teams are now so vast that they have to specialise, which further compounds the issue.
Shot down in flames for this? Its the truth!
Re: Aerodynamics of Porpoising
Posted: 03 Apr 2022, 21:45
by vorticism
Short list of culprits:
-tire compression
-fluttering floor
-steady state floor flex
-suspension damping
-front floor positive lift vs total car downforce
-plank-ground proximity effects
-strake-ground proximity effects
-sidepod effects
I agree with Andi76, if problems are hard (or maybe close to impossible) to model and simulate, experience becomes worth a lot more suddenly. While you can't accurately predict what's going to happen from experience, you can make educated guesses. And you will have reasonable expectations for possible problems and potential solutions.
I think that teams who have staff that has experience with porpoising and ground effect cars might have been quite a bit more prepared. Even if they didn't know whether they'll have porpoising issues, they may have thought about possible reasons and solutions before they even had the car on track for the first time, just in case there is porpoising. You can only do that, if you have experience with this problem. Then, when the problem occurs for real, you can compare it to your expectations and start trying to solve it immediately because you already have a basic understanding of what's going on.
Re: Aerodynamics of Porpoising
Posted: 04 Apr 2022, 01:31
by Greg Locock
The proper way of modelling this is a co-sim with an FEA model, CFD, and an MBD. The three models talk to each other at every time step, and then decide on the inputs for the next time step. This chews through CFD CPU cycles like nobody's business.
We slightly reduce the difficulty by incorporating linear FEA into MBDs, using flex bodies, so it is only a 2 way co-sim. But the CFD is the big one.
I agree with Andi76, if problems are hard (or maybe close to impossible) to model and simulate, experience becomes worth a lot more suddenly. While you can't accurately predict what's going to happen from experience, you can make educated guesses. And you will have reasonable expectations for possible problems and potential solutions.
I think that teams who have staff that has experience with porpoising and ground effect cars might have been quite a bit more prepared. Even if they didn't know whether they'll have porpoising issues, they may have thought about possible reasons and solutions before they even had the car on track for the first time, just in case there is porpoising. You can only do that, if you have experience with this problem. Then, when the problem occurs for real, you can compare it to your expectations and start trying to solve it immediately because you already have a basic understanding of what's going on.
I think the very first test already made the "worth of experience" in that regard visible. If you take a look at Ferrari - they appeared at Barcelona with an extremely stiff suspension set-up. From the very first minute, while most of the other teams used suspensions set-ups which were quite soft compared to Ferrari. In my opinion this was a very early example and proof of this "worth of experience". Ferrari knew, before they even had the car on track, that a stiff suspension will be required with these kind of cars. That was something that pretty sure came from someone having experience with ground effect cars.
Pat Fry talking about porpoising being connected to floor stiffness and how teams with extra floor "real state" might be suffering more from it.
"We put a lot of stiffness in the floor and our wide top body also allows you a stiffer installation. So that's helped us out, to be honest."
Re: Aerodynamics of Porpoising
Posted: 06 Apr 2022, 03:02
by vorticism
Wonder if he means steady state deflection negatively changing the floor shape, or flutter at the floor extremities. Or both.
