[MVRC] GR_23

[G-raph]

Hi everyone!

As we are in the MVRC off-season, I’ve opened this thread to share some insights into my 2-year journey to winning this amazing championship.

I hope you will enjoy it, but more importantly that it will spark some interesting discussion about the Challenge and F1 aerodynamics. So please ask any question you like and share any observations about my car or yours in this thread.



I’ll start will some simple stats and pictures today.

I decided to enter the Challenge after looking at the 2020 cars and results. Although the cars were looking great and creative, I thought they were missing key aspects of F1 aero performance and that I could do much better with very little effort.

So I started designing a 2022 MVRC car, learning a new CAD software in the process (FreeCAD), intending to not run any CFD but still expecting to win the first race straight away. It turned out I was very wrong!

I finished the CAD model a little bit ahead of the first race so I had a bit of time to run it in Mflow. There was a few flow separations that I tried to fix quickly with a second design iteration, but I was still confident.

In hindsight, finishing 5th in that first race was a very good effort. But it made me realise the level of this championship was much higher than expected, and that proper development work was needed. I really should have quit at that point, but for whatever reason I didn’t.

I won the 3rd race of the season after fixing all the flaws of my initial concept, which sort of proved my point, just 2 races later. Great, job done? Except that the impressive development pace of the competitors quickly made me fall behind again.

So if I ever wanted to win this thing, it became clear that I had to put some serious effort, which is what I did in the off-season between 2022 and 2023.

Unfortunately I don’t have any pretty graph to show how my performance level evolved with development (like I’ve seen elsewhere), but here are a few stats that I hope you will find interesting :


Number of design iterations / CFD simulations run before each race :

2022 Race 01 (finished 5th) : 2
2022 Race 02 (finished 4th) :15
2022 Race 03 (finished 1st) : 16
2022 Race 04 (finished 3rd) : 7
2022 Race 05 (finished 2nd) : 8

Additional runs with 2022 regs : 12

2023 Race 01 (finished 1st) : 27 (21 designs + 6 ride height changes)
2023 Race 02 (finished 1st) : 12
2023 Race 03 (finished 1st) : 12 (mainly Monza-specific package)
2023 Race 04 (finished 1st) : 21
2023 Race 05 (finished 2nd) : 9

That is a grand total of 48 simulations for the 2022 car, and 93 simulations for the 2023 car.


To illustrate that, here are a couple of gifs showing the geometrical evolution of my car over those 2 years, and the Cps level underneath it. You can see the rapid improvement during 2022, the very large step at the start of 2023 (helped by the new tyres, suspensions and brake ducts)… and then the development struggle (more on that in future posts).

[yinlad]

I do love these posts. Looking forward to what you bring for 2024.

2023 Race 04 (finished 1st) : 21
2023 Race 04 (finished 1st) : 9

should read

2023 Race 04 (finished 1st) : 21
2023 Race 05 (finished 2nd) : 9

I suppose?

[G-raph]

Thanks! That was indeed a bad copy-paste. Corrected now.

[variante]

Rather amazing that you managed to reach that level of performance (especially right at the 1st race) with so few simulations. I did run about twice as many.
In my defence, i fixate a lot on thing that don't necessarily carry a lot of performance, just to learn of for fun. But still...

What i want to ask is: why did you choose that gentle convex diffuser? to better preserve the vortices coming from the fences?

[G-raph]

I usually make several changes at once to limit the number of CFD simulations. For example I could combine changes to the floor fences, the cooling outlet and the beamwing, and then try to understand the individual contributions from a single CFD run. So I might have tried as many shapes as you, but with less CFD simulations (and quicker ones since they were all on fast settings).

Your question is a great one, and the simple answer is : That's a design choice I made when I drew my first 2022 car, and I never have even evaluated anything different.

My diffuser is still a classic convex-concave-convex design, but you are right that the initial convex kickpoint has a very large radius. That is because I wanted to start the diffuser as far forward as possible, and also spread the suction onto a larger area rather than having aggressive pressure gradients.

My whole car design philosophy was to maximise loading in the front and middle part of the floor, rather than in the diffuser, for 2 reasons :

1- Because that generates relatively balanced downforce, so you don't have to go crazy with the front and rear wings. A very far forward diffuser kickpoint will help with that, as well as making the fences vortices stronger and healthier.

2- Because having too much suction in the diffuser makes controlling the diffuser edge vortices quite difficult. Hence getting the kickpoint forward and spreading it to avoid a strong peak of low pressure near the diffuser edges.


Now, having developped this car for a bit and seen your particular diffuser kickpoint design, I think there is a better solution somewhere. Especially as ironically, I struggled to get the balance rearward enough (more on that later) in 2023. I'll definitiely investigate different options for 2024.

[G-raph]

As you all know, there was a massive performance step between the last race of 2022 and the first race of 2023.

End 2022 :
Total downforce : Cl = 4,825
Total Drag : Cd = 1,599
Efficiency Cl/Cd = 3,018

Start 2023 :
Total downforce : Cl = 6,073
Total Drag : Cd = 1,592
Efficiency Cl/Cd = 3,813

That’s +25% downforce for the same drag, despite very similar floor geometries between the 2 cars!


Most of this performance improvement came from changes to the regulations :
- More realistic front and rear tyre shapes.
- Ability for each competitor to run their car at the desired ride height.
- Removal of the mandatory front and rear brake duct deflector surfaces, and allowance for each competitor to design their own.
- Re-designed mandatory front and rear suspension components.


Today, let’s talk specifically about wakes!

On an F1 car, the most problematic wakes come from the 4 tyres and the open cockpit area, as the regulations don’t allow for much geometry around them. F1 aerodynamicists’ main priority is to make sure their car doesn’t hit its own dirty air!

This post is about the most important wake of all : the Front Wheel Wake!

As it is by definition formed at the front of the car, it has the potential to cause chaos downstream, particularly to the floor, sidepods and rear wing.

The new tyres for 2023 produce inherently a much smaller (and more realistic) wake, so all MVRC competitors were helped by that. But I also spent a lot of time in the off-season working on the front brake duct winglet design, carefully iterating it to further reduce the size of the front wheel wake.


This GIF shows a constant X slice at the start of the floor and sidepod of Cp_total : essentially the energy level available in the flow. You can see how the front wheel wake has reduced, and how much more energy is available around the floor on my 2023 car.




(Please note this comparison is not exactly at the same location for the 2 cars, due to a change in total car length, but the conclusions are still valid).

The next post will be about the other wakes at the back of the car!

[Stu]

The reduction in the wheel wakes is phenomenal! My eyes are also drawn to the reduction in losses around the bodywork, this seems in the 2022 instance to start generating in front of the cockpit (and expands from there).
Is this caused by the size & intensity of the wake from the front wheels (and therefore solved by reducing the size & intensity of the wheel wake); or do you have some other mechanism in place to cause the change?
The losses from the open cockpit are also dramatically reduced.

I have wondered whether the move to centreline cooling in ‘the real thing’ was really about reducing the losses from the cockpit & halo by ‘ingesting’ and then controlling them rather than allowing them to destroy flows downstream.

[G-raph]

My eyes are also drawn to the reduction in losses around the bodywork, this seems in the 2022 instance to start generating in front of the cockpit (and expands from there).
Is this caused by the size & intensity of the wake from the front wheels (and therefore solved by reducing the size & intensity of the wheel wake); or do you have some other mechanism in place to cause the change?

It is difficult to be 100% sure, but I don't think this has anything to do with the front wheel wake reduction.

The re-designed mandatory Front Suspension parts (much better aligned to the flow) and the mesh refinement on them for 2023 (as part of the ride height adjustement tool) are the main reason for this loss reduction.
Having said that I have also improved the junction between the front wing and the nose, and the high sidepod leading edge with the various vanes in front of it are also turning these front wing and front suspension wakes down and away from the cockpit much more effectively.

The losses from the open cockpit are also dramatically reduced.

That's mainly because my 2022 car was very poorly designed in this area, so there was some easy clean-up steps to take for 2023.

I have wondered whether the move to centreline cooling in ‘the real thing’ was really about reducing the losses from the cockpit & halo by ‘ingesting’ and then controlling them rather than allowing them to destroy flows downstream.

I don't think centreline cooling reduces cockpit losses in any way, but yes it is about guiding these losses towards a benign region in-between the upper rear wing and the beamwing, where you would also exit as much cooling flow as possible.
I'll talk in a little bit more detail about cooling in my next post, so hopefully you'll see why the real F1 cars are using centreline cooling.

[G-raph]

Wakes – part 2, with less words and more pictures!


I also spent a lot of time in the off-season working on the car’s upper bodywork, with the target of delivering clean flow and downwash to the rear wing and beamwing, as my 2022 car was lacking in that aspect compared to other competitors.
The difficulty is to manage the wake from the open cockpit area, and to send the low energy cooling flow to the right place.

- The new sidepods induce more downwah generally towards the back.
- The much tidier engine cover and details around the driver have reduced the cockpit wake.
- The cooling outlet has been moved as outboard as possible, aiming to send cooling losses outside of the rear wing.
- And of course, the massive airbox sails are here to enhance these effects.

The first GIF show streamlines of the cooling flow, with an added illustration of the airbox sail vorticity. You can see how these cooling losses are just missing the rear wing on the 2023 car, which was not the case in 2022.



The second GIF is an X-slice of total pressure just ahead of the rear wing. You can see how much more energy is available to the rear wing in 2023, and the trace of the rotating flow induced by the airbox sails vortices!



(Please note these comparisons are not exactly at the same locations for the 2 cars, due to a change in total car length, but the conclusions are still valid).

Finally, another wake that is important to take care of is the rear wheel wake, as it can interact with the diffuser and reduce its effectiveness. The new tyres shape was an improvement, but the biggest benefit came from designing our own rear brake duct winglets.

You could already see in the previous GIF that the rear wheel wake has not been able to enter into the diffuser at all on the 2023 car.
This third GIF is another X-slice behind the car, confirming all of what was described above.




In conclusion, along with the front wheel wake improvement shown in my previous post, the improved management of the cockpit, cooling and rear wheel wakes have contributed to a large step in aerodynamic performance from 2022 to 2023.

I hope you found this interesting, as always please get in touch if you have any question or observation.

I have wondered whether the move to centreline cooling in ‘the real thing’ was really about reducing the losses from the cockpit & halo by ‘ingesting’ and then controlling them rather than allowing them to destroy flows downstream.

I think the move to centreline cooling is a necessity for F1 teams, to keep the low energy cooling flow in a benign region between the rear wing and beamwing in most (or ideally all) conditions.

You can see that I am only just able to miss the rear wing with my cooling flow, despite :
- cooling louvres more outboard than what is allowed in F1
- a massive airbox sail that F1 teams can't have
- only straight line condition to worry about

[LVDH]

Very cool posts, thank you a lot for this. It is very cool to see how these cars get developed. And as already noted, you did amazing work with a pretty limited number of simulations. I think some teams run these numbers between races.

[G-raph]

Hi again!

After covering the large performance step between 2022 and 2023, this second series of posts will focus on in-season development. Or rather the lack of, and how I started the 2023 season 1s/lap ahead of everyone but barely hung-on to a podium at the last race.

To understand how things went wrong, we will need to talk about correlation .

Correlation is a hugely important aspect of modern F1 aerodynamics, and is about how each team’s racecar performs relative to expectations from their tools, Wind Tunnel and CFD.

Why would it matter for a CFD championship such as the Mantium Challenge, you may ask?

It matters because the CFD model that I (and other competitors) use for regular development (referred as “Fast Settings”) is a much less refined (by almost 3 times the number of cells) version of the one used for the official runs (referred as “MVRC Settings”), which is itself roughly 20 times less refined than a typical F1 CFD run.

Fast settings : ~3M cells (for half a car) / 2000 iterations

MVRC settings : ~8M cells (for half a car) / 5000 iterations


You can see on the GIFs below the differences between the Fast and MVRC settings (for my Race 05 car). The more refined the mesh is, the more accurately the various flow features (wakes and vortices) are captured by the CFD model.






This has a big effect on the overall pressure field around the car, and of course the downforce results :



Fast settings (Race 05) :
Total downforce : Cl = 5,465
Total Drag : Cd = 1,591
Efficiency : Cl/Cd = 3,435
Center of Pressure : CoP = 1,974

MVRC settings (Race 05) :
Total downforce : Cl = 5,970
Total Drag : Cd = 1,594
Efficiency : Cl/Cd = 3,744
Center of Pressure : CoP = 1,913


If you wonder why I’ve quoted CoP above, that’s because it will be the topic of the next post!

[yinlad]

If you wonder why I’ve quoted CoP above, that’s because it will be the topic of the next post!

CoP shift between settings is literally the bane of my existence

[variante]

We manage the diffuser area quite differently but, interestingly, the downforce gains from fast settings to mvrc settings are the same for both of us. But I have been graced with a smaller CoP shift.

[G-raph]

CoP shift between settings is literally the bane of my existence

We manage the diffuser area quite differently but, interestingly, the downforce gains from fast settings to mvrc settings are the same for both of us. But I have been graced with a smaller CoP shift.

I guess the size of the CoP shift doesn't matter that much. It is more about its consistency, especially when you play around with floor designs.

[G-raph]

The first correlation issue I have been fighting with during the Mantium Challenge 2023 season was related to the Centre of Pressure (CoP), more commonly known as Aerodynamic Balance (AB).

There is obviously no such thing as a universally perfect balance for a F1 car, as this depends on so many things like mechanical balance, tyres, fuel load or corner type.

However, Max Taylor’s Laptime Simulator used in the Challenge has an optimum CoP of 1,92 (with the front axle being at 0 and the rear axle at 3,6) to minimise lap time. This is equivalent to 43,5% AB (meaning 43% of total downforce acting on the front axle, and 57% on the rear axle). This is in-line with how modern F1 cars operate, which ensures competitors come up with realistic designs.

During the first 3 races, my car’s balance was around 2% too far forward, because as indicated in my previous post, I couldn’t rely on the Fast Settings to evaluate balance exactly. So I had to guess based on my 2022 car, and got it wrong.

This costs me around 0,2s/lap for these first 3 races.
So for the last 2 races, I corrected the car’s balance to get that laptime back, as you can see in the overall results table :


Race 02 :
Efficiency : Cl/Cd = 3,869
Center of Pressure : CoP = 1,857
AB = 45,4%

Race 05 :
Efficiency : Cl/Cd = 3,744
Center of Pressure : CoP = 1,913
AB = 43,7%


It took me a while as I was hoping to find more rear downforce during in-season development to cure the problem, but this never came.

In the end I did this by simply reducing the front wing chord, and increasing the rear wing outboard camber, as you can see on the GIF. It looks quite small and would be difficult to spot on TV (between 2 teammates for example) if you didn’t have such a clean comparison, but it shows how finely tuned these machines are.



You can also see how this affected the pressure field on the wings themselves (ignore the rest of the car changing, it didn’t affect balance).



The front wing is a very efficient device, whilst the rear wing is not. Therefore, for maximum efficiency you would ideally have a big front wing and a small rear wing. But for that you need the rest of the car to generate the optimum balance, which unfortunately my car did not.

So I lost some efficiency in the process as you have seen above, but was it worth it? Well, that drop in efficiency costed me… you have already guessed it… around 0,2s/lap!