CFD - 2022 F1 Car

[DChemTech]

That underbody tunnels are less affected by wakes than flat floors with a diffuser is one of those truisms which isn't necessarily true. Certainly I think the balance of the cars should be less affected, but the main improvement with regards to the downforce loss in the wake is the big rear wing pulling the wake upwards. That in turn means there's less wake at ground level to go into the floor tunnels.

I agree that lower drag cars would probably require less power to prevent top speeds being too outrageous, but then you'd want less mass so you could accelerate the cars out of corners. I like the Ben Bowlby LeMans Deltawing approach of 1/2 mass, 1/2 power, 1/2 drag, 1/2 fuel. I think the plan for 2024 sounds like 3 cylinder opposed cylinder engines at which point I think they should also be aiming for a significantly lower fuel allowance (at least down to 75kg) to really highlight/drive economy while obviously maintaining good racing. Current

I also like the Frank Dernie idea of super hard tyres which last a full race plus the practice sessions for the next event (obviously manufacturing and transporting fewer tyres to each track) - it's often overlooked in the aero issue of overtaking that a single rubbered in line plus the detritus off-line makes racing even more difficult. If the cars are grip limited too then drivers can make mistakes which can lead to further opportunities.

Oh, well i hope Nikolas & co have got it right with the tunnels, and also actually cut the outwash this time. Yes the cars are too heavy aren't they, anyway, they ought to abandon all those minimum weights, raise the crash test levels a LOT and let teams fight it out on weight, including the battery. Liberty seem to want to force close racing in F1 like F2, forgetting that hardly anybody cares about F2 BECAUSE the cars are all the same!!

Tyres, well F1 is the biggest example ever of unintended consequences isn't it. If they went to no pitstops i think they'd have to go to Ross's reverse championship grids, otherwise too often the fastest car would start in front and just go round and round there

I doubt the reason so few people are interested in F2 is because it's a spec series. The biggest reason is probably simple that it's number 2, meaning it's simply not the top participants. You see the same in every sports - soccer is exactly the same game in the premier league and second league, yet audiences of second league are a fraction of the premier.

[izzy]

I doubt the reason so few people are interested in F2 is because it's a spec series. The biggest reason is probably simple that it's number 2, meaning it's simply not the top participants. You see the same in every sports - soccer is exactly the same game in the premier league and second league, yet audiences of second league are a fraction of the premier.

Yes it's about status, but spec has zero engineering status, no awesomeness of design, complexity, teamwork, problem-solving etc etc. That's why the spec series have less status: they represent less

[Just_a_fan]

"Junior" formulae used to be more watched back when the stars did more than just F1. Jim Clark, for example, raced (and died) in a Formula 2 race. Of course, back then the F1 calendar had many fewer races so there were big gaps between F1 races. The stars used to race in other series to fill the time and meet contractual obligations.

Of course, back then, motorsport was mostly watched by people track side with little TV coverage available for those who couldn't go to the track. So the people who were interested in motorsport would watch the junior formulae because they were at the tracks. Today, the majority of "fans" never go to tracks to watch - it's all viewed on screen, be that TV, internet etc. So the likes of F2 are seen as being nothing more than a feeder series to F1. Many people want to see "stars" these days so F1 attracts those types as "fans". Most of these people care not one jot for the tech side of the sport - they're interested in famous people, glamour etc.

If Hamilton, Vettel, Verstappen all went and did F2 races in between F1 races, you can bet that F2 would be much more popular than it is now, spec series or not.

But this is massively OT and risks diluting this excellent thread so we should leave it there and get back to the CFD of the 2021 cars.

[DChemTech]

I doubt the reason so few people are interested in F2 is because it's a spec series. The biggest reason is probably simple that it's number 2, meaning it's simply not the top participants. You see the same in every sports - soccer is exactly the same game in the premier league and second league, yet audiences of second league are a fraction of the premier.

Yes it's about status, but spec has zero engineering status, no awesomeness of design, complexity, teamwork, problem-solving etc etc. That's why the spec series have less status: they represent less

I'm not sure how much it matters for casual viewers. But I do personally agree that F1 is interesting for me because of the engineering aspects. In that respect, my preference would be a wider technical window of operation, but with a tight budget cap. That's the only way to make it a competition on which engineering team is most creative, instead of which team has the deepest pockets. (To stimulate close racing, maybe there should be limitations on certain performance aspects instead of on technical possibilities - e.g. enforce a maximum wake strength at X meters behind the car in a standardized wind tunnel test, but leave it to teams how to achieve that)

Anyway, this is off topic here, so I'll shut up on this point and get back to enjoying colorful pictures now

[DChemTech]

A more CFD-technical question that I have;
You state using SST with wall functions. I thought that the power of SST was, however, in the near-wall regions - properly (for RANS, at least) resolving boundary layer/separation effects. Hence, I though a resolved mesh (Y+ of ~1 in the first layer) is required to make proper use of the SST formulation - and that using SST with wall functions essentially reproduces the k-epsilon model (the bulk formulation of SST). Am I mistaken here? Do you have some comments on what the effect of wall functions will be in this case?

[Vyssion]

A more CFD-technical question that I have;
You state using SST with wall functions. I thought that the power of SST was, however, in the near-wall regions - properly (for RANS, at least) resolving boundary layer/separation effects. Hence, I though a resolved mesh (Y+ of ~1 in the first layer) is required to make proper use of the SST formulation - and that using SST with wall functions essentially reproduces the k-epsilon model (the bulk formulation of SST). Am I mistaken here? Do you have some comments on what the effect of wall functions will be in this case?

Bit of a technical answer, and one which is dependant on the solver used as well, but I hope this helps explain it:

The flow close to a wall has a viscous sublayer which depends on a few different parameters, such as roughness and the velocity components. It is not too difficult to think about boundary layers, and to realise, that as your Reynolds Number increases, your boundary layer thickness will decrease. You can check the equations, and see that theres an inverse relationship of boundary layer thickness to freestream velocity too.

It is important to keep in mind that the standard models typically used in solvers, are based on isotropy... which is an assumption that is not really valid most of the time... The main disadvantage of these standard models is related to the fluid behaviour within the viscous sublayer. The "damping" of the velocity normals on the wall, is much higher than tangential to the wall, which makes the isotropic assumption even worse. If you have high Re flows, the sublayer thickness decreases quite a bit.. and so, you have two options (most of the time), which would allow you to still resolve the velocity change within the sublayer:

• Resolving the sublayer
• Model the sublayer

Experimentally, it has been found that the velocity behavior in the sublayer follows a logarithmic law. Thats why we can use "Wall Functions" which typically are logarithmic functions. However, the log law is only valid within a set range. If you are using wall functions, you model the sublayer with the log law equation, and therefore the first cell height should be somewhere close to the maximum y+ range you expect to see (you can do a rough blasius flat plate calculation, and correct for curvature based on how aggressive you feel your CAD is in the critical area). If your first cell is too small, you will introduce inaccuracies because the second cell would be still in the log law region, but it will not be applied to it. If you have y+ << 1 there is no need to use wall functions because you are already resolving the viscous sublayer.

Within ANSYS, k-omega SST has only one wall function. One of the benefits of the k-omega SST model is that it will automatically use the low-Re formulation in the viscous sublayer and will use its wall function calculation if the cell height is within the log-law layer. This refers to its "automatic" wall-function... the only one it has. It uses a linear law for omega within one regime, and another log law for omega within the refined regime.

If I lift a line straight from the solver theory guide:
"The wall boundary conditions for the equation in the models are treated in the same way as the equation is treated when enhanced wall treatments are used with the models. This means that all boundary conditions for wall-function meshes will correspond to the wall function approach, while for the fine meshes, the appropriate low-Reynolds number boundary conditions will be applied"

This part is talking about the k-equation. Enhanced Wall Treatment and Enhanced Wall Function mean almost the same thing. Enhanced wall functions are the blended linear & log standard laws. Enhanced wall treatment uses these enhanced wall functions. And again from the solver guide:
This means that all boundary conditions for wall-function meshes will correspond to the wall function approach, while for the fine meshes, the appropriate low-Reynolds number boundary conditions will be applied.

Now for our case...

My PC can only handle a certain number of million elements. It means that I have to be very careful with how I apply my prism layers and growth rates, in order to ensure that I can "capture the bits I want to, and leave the less interesting bits to be analyzed roughly". What this means is that, for example on the front wing elements, I resolve the boundary layer down to a y+ of about ~0.5 whilst on other areas, such as the top of the nose, I resolve it only to around 60-100. Because of how this "automatic wall function" is applied, the SST model will be used to a pretty decent extent in somewhat critical areas, whilst in less "impactful" areas on the car's performance, it will default to a "wall-function based" solver: which you are correct, will imply something akin to k-epsilon. Also, due to mesh quality, I utilise layer compression, rather than stair-stepping within the prism layers, in order to better capture whats going on. In areas such as gap and overlap of flaps, this is another area in which the local y+ will be quite a lot lower than some of the larger areas on the car.

At the end of the day, CFD in RANS, is literally just "modeling" to begin with. When I get my new PC soon, I will be able to better mesh and capture critical areas, but if I was to run a fully resolved viscous sub-layer, I would need a lot more computational time and power... maybe I'll get lucky and 128Gb will be enough to solve (because often when you resolve your boundary layer cells to that level of refinement, you need to solve in double precision just to "locate" the cell nodes in the correct spot - else the solver will truncate coordinates, and spit out a negative cell volume error).

Note: turbulence is not my "expertise" per se, but I do try to understand the problems that I solve at work, to a fundamental level... I hope that this is correct, but by all means, if I have made a mistake, feel free to jump in and correct me - I love learning!!
"When I meet God, I am going to ask him two questions: Why relativity? And why turbulence? I really believe he will have an answer for the first." -- Heisenberg

[strad]

So the likes of F2 are seen as being nothing more than a feeder series to F1. Many people want to see "stars" these days so F1 attracts those types as "fans". Most of these people care not one jot for the tech side of the sport - they're interested in famous people, glamour etc.

If Hamilton, Vettel, Verstappen all went and did F2 races in between F1 races, you can bet that F2 would be much more popular than it is now, spec series or not.

.
MAN... I couldn't agree more. Back when I was young you had the likes of Jim Clark and other top stars driving in F2 and thus more interest.
Kind like NASCAR and the NASCAR Xfinity Series.. When the top drivers weren't there they couldn't draw fans but now they fill the grandstands.
.
I also disagree about people watching for the creativity etc.
Most don't have a clue and the FIA now design the cars thru their rules, and have done their best to exclude creative thinking or design.

[DChemTech]

It would be pretty cool if the big F1 stars occasionally would race in spec series to really judge their comparative driving skills.

@Vyssion, thanks for the elaborate answer. Resolution is indeed always a hurdle
My background is mainly in reactive bulk hydrodynamics, where wall effects are typically not so relevant & standard wall functions are the default. In my field, most studies use (realizable) k-epsilon models; SST does not seem to yield a benefit, which is logical from the perspective that the free-shear formulation of SST is essentially k-epsilon. I did a few minor projects related to boundary layer effects where we did use SST, but there the geometry was sufficiently simple to fully resolve the boundary layers. I also tested SST on a coarser mesh there, but tended to have divergence issues (while realizable k-eps with std. wall fun. ran fine, but did indeed show considerable differences in near-wall velocity profile). So hence I was wondering what your experience in SST with coarse near-wall grids was, and if you would still benefit from the k-w formulation near the wall in that case.

[Vyssion]

It would be pretty cool if the big F1 stars occasionally would race in spec series to really judge their comparative driving skills.

@Vyssion, thanks for the elaborate answer. Resolution is indeed always a hurdle
My background is mainly in reactive bulk hydrodynamics, where wall effects are typically not so relevant & standard wall functions are the default. In my field, most studies use (realizable) k-epsilon models; SST does not seem to yield a benefit, which is logical from the perspective that the free-shear formulation of SST is essentially k-epsilon. I did a few minor projects related to boundary layer effects where we did use SST, but there the geometry was sufficiently simple to fully resolve the boundary layers. I also tested SST on a coarser mesh there, but tended to have divergence issues (while realizable k-eps with std. wall fun. ran fine, but did indeed show considerable differences in near-wall velocity profile). So hence I was wondering what your experience in SST with coarse near-wall grids was, and if you would still benefit from the k-w formulation near the wall in that case.

My M.O. changes based on what "level" of accuracy I am targetting. By default, I always start with SST, because it (arguably) has had the most V&V performed with it through its extensive use in academia and industry. It also means that, should my mesh not be the smoothest and homogenous, at least I won't be hamstrung by it (mostly). That being said, there are specific flow regimes (usually on the lower Re side - typical of correlation work) where SST tends to underpredict CLmax and prematurely stall. Not too many people are aware of this, but it comes into its own, particularly, when you add in the transition equations for Momentum Thickness and Boundary Layer Turbulent Kinetic Energy.

This being said there is a revision, which is quite tempramental to get working, called k-kL-omega which does a MUCH better job, however, it has much more stringent mesh requirements. It does solve faster than the k-omega-SST w/ transition, due to having one fewer equation. This is the model I tend to default to when I really need to accurately predict near wall behaviour - and I know of a few cases in F1 where certain aerodynamic devices which teams ran successfully, were down to getting this turbulence model working well.

This being said, it's still all RANS based (with the occasional URANS), and we know that RANS does a mediocre job at predicting stall cells, and a dubius job at best with post-stall behaviour... so its a balancing act that you run between your residuals (how well you solve your control volumes, i.e. cells) and imbalances (how well you solve your domain inlet/outlets etc.)

[Blackout]

Awesome job you two.
And you should read the April 2020 issue CFD 2021 analysis of racecar engineering. It has interesting similarities and differences to your analysis. And more than two people did it.

• CzS = -4.95
• CxS = 1.80
• Front Wheel wake is pretty crazy now... we will work on this
• Going to reduce pitch setting of FW flaps
• Inboard floor fence vortex isnt under control (just spreads out)
• 2021 Force Breakdown = Floor (50%), FW (37%), RW (25%)
• Compared to Perrinn = Floor (55%), FW (30%), RW (40%)
• Higher than 100% is due to Lift generated on the chassis and wheels (6% lift on 2021 wheels, 9% lift on Perrinn)
• Balance of 2021 is ~49% which is quite far forward, so we will correct this (starting with FW flaps as mentioned above)
• Surprisingly large amount of low pressure below the car
• Front suspension is stalled
• Top of floor inlet is stalled
• Rear of Lower sidepod expansion has stalled
• RW flap stalled in curved EP sections (and slightly along TE) and RW as a whole is very draggy

Their numbers:
CzS = -4.94
CxS = 1.53
Balance %front: 40%
DF Breakdown = Floor (around 61%), FW (around 24%), RW (around 27%)

It's only around 7$
https://www.racecar-engineering.com/new ... e-out-now/

[strad]

"Junior" formulae used to be more watched back when the stars did more than just F1. Jim Clark, for example, raced (and died) in a Formula 2 race. Of course, back then the F1 calendar had many fewer races so there were big gaps between F1 races. The stars used to race in other series to fill the time and meet contractual obligations.

Of course, back then, motorsport was mostly watched by people track side with little TV coverage available for those who couldn't go to the track. So the people who were interested in motorsport would watch the junior formulae because they were at the tracks. Today, the majority of "fans" never go to tracks to watch - it's all viewed on screen, be that TV, internet etc. So the likes of F2 are seen as being nothing more than a feeder series to F1. Many people want to see "stars" these days so F1 attracts those types as "fans". Most of these people care not one jot for the tech side of the sport - they're interested in famous people, glamour etc.

If Hamilton, Vettel, Verstappen all went and did F2 races in between F1 races, you can bet that F2 would be much more popular than it is now, spec series or not.

But this is massively OT and risks diluting this excellent thread so we should leave it there and get back to the CFD of the 2021 cars.

Right on the money JaF.
I posted something along these lines in the past.
I believe the largest number of viewers/fans don't know or care about the technical side. Their eyes glaze over when you start talking CFD and drag coefficients.
Quite frankly a large percentage are confused by all the technicality that makes up modern F1. I think it's why some have tuned out.
We don't represent the average viewer/fan.
Much like when the empty stands at Busch races filled when they started filling the grid with the Cup drivers the stands began being filled.
People want to watch the stars. Put Vettel and the other stars in F2 cars and they couldn't print enough tickets.

[jjn9128]

Awesome job you two.
And you should read the April 2020 issue CFD 2021 analysis of racecar engineering. It has interesting similarities and differences to your analysis. And more than two people did it.

We've seen it Miqdad Ali posts here sometimes as dynamicFlow. We actually conversed about our studies and compared numbers as we were both doing them I feel the two studies are complimentary, as while we go into more detail on the wake and aero of the single car he covered more of the effect on a following car, we came to similar conclusions too. It's telling how his following case is worse than the FIA/FOM prediction, almost like they used their best case to present publicly...

I believe it's just Miqdad who does all the CAD and CFD then McBeath comes in and does the write up or edits the write up.

[GM7]

With the 2021 regulation being delayed to 2022 and Indycar using the aeroscreen since the beginning of the year, it is not impossible to see this protection device being implemented by 2022. What would be the global aerodynamic impact of this introduction and particularly in the side of the engine air box ?

[Just_a_fan]

With the 2021 regulation being delayed to 2022 and Indycar using the aeroscreen since the beginning of the year, it is not impossible to see this protection device being implemented by 2022. What would be the global aerodynamic impact of this introduction and particularly in the side of the engine air box ?

It's really a halo screen rather than the much hoped-for aeroscreen. And it's even less pleasing to the eye than the halo.

I'd bet it would have a big impact on the downstream aero of the cars - the rear wing might take a big loss, for example. It would be interesting to see some plots of the flow with aeroscreen.

[Stu]

That underbody tunnels are less affected by wakes than flat floors with a diffuser is one of those truisms which isn't necessarily true. Certainly I think the balance of the cars should be less affected, but the main improvement with regards to the downforce loss in the wake is the big rear wing pulling the wake upwards. That in turn means there's less wake at ground level to go into the floor tunnels.

I agree that lower drag cars would probably require less power to prevent top speeds being too outrageous, but then you'd want less mass so you could accelerate the cars out of corners. I like the Ben Bowlby LeMans Deltawing approach of 1/2 mass, 1/2 power, 1/2 drag, 1/2 fuel. I think the plan for 2024 sounds like 3 cylinder opposed cylinder engines at which point I think they should also be aiming for a significantly lower fuel allowance (at least down to 75kg) to really highlight/drive economy while obviously maintaining good racing. Current

I also like the Frank Dernie idea of super hard tyres which last a full race plus the practice sessions for the next event (obviously manufacturing and transporting fewer tyres to each track) - it's often overlooked in the aero issue of overtaking that a single rubbered in line plus the detritus off-line makes racing even more difficult. If the cars are grip limited too then drivers can make mistakes which can lead to further opportunities.

I totally agree on the Bowlby/Deltawing concept. I thought that it was a real shame that IndyCar didn’t go with it (my understanding is that the original concept was for their first Spec chassis?).

The wish that I could do CFD....