Parametric Racecar Aerokit design [MVRC]

[machin]

2) I am not sure, but I think that the external geometry of TF's front wing seems to be designed to seal the sides of the floor instead of feeding them. It would be a good thing (I tried to copy it during the season) if coupled with a geometry that could feed the central part of the floor (ex. high nose), on the contrary (even not my philosophy) Variante's choice to improve airflow from the sides gives better results.

Interesting.... In what "form" do you propose the "seal" is created? A vortex? Or by significant out-wash that counteracts any tendency for flow to get drawn in from the sides?

The wheel fairing shape is quite similar on Aratz's and Variante's cars, but Aratz has the detailed foot plate and Variante has those unique "dive plane" additions...and of course Variante has his radiused floor edge...

[CAEdevice]

2) I am not sure, but I think that the external geometry of TF's front wing seems to be designed to seal the sides of the floor instead of feeding them. It would be a good thing (I tried to copy it during the season) if coupled with a geometry that could feed the central part of the floor (ex. high nose), on the contrary (even not my philosophy) Variante's choice to improve airflow from the sides gives better results.

Interesting.... In what "form" do you propose the "seal" is created? A vortex? Or by significant out-wash that counteracts any tendency for flow to get drawn in from the sides?

The wheel fairing shape is quite similar on Aratz's and Variante's cars, but Aratz has the detailed foot plate and Variante has those unique "dive plane" additions...and of course Variante has his radiused floor edge...

Yes, the detailed foot plate should be there to generate a vortex. I tested it but it reduced the floor efficiency with my design.

The winglets you can see on my car (front wheels cover) also generate a vortex, but placed above the floor plane. Honestly I am not completely sure about the way it works, but it influences floor and diffuser side channels efficiency.

I also tried something like a rounded floor but it did not worked.

[variante]

The question from me is what fundamentally is different between Variante's car and Aratz's; they both have big front diffusers with the majority of the air coming off that going through the side-pod and Heat Exchanger area. Both cars have full-width sidepods, and yet Variante's car is pulling a lot more flow into the diffuser from the sides of the floor.... but nothing looks "wrong" with Aratz's diffuser from the images we have....

The magic of aerodynamics...
The images TF released are very small, but what I think is happening is that TF is using a too aggressive diffuser (great ramp angle, small transition radius). This solution may actually work, but it would need to be coupled with some big vortices helping the flow to stay attached to all the surfaces and goin through the imposed expansion.

On the contrary, TF's diffuser is receiving air from the front, with a wrong angle for the strakes, therefore those are not capable of generating the necessary vortices, thus no further air is sucked by the diffuser, which stalls immediately.
If he manages to start that chain reaction, he will gain a lot of downforce very quickly (and I'm pretty sure he managed to do that in the past, with great performances achieved).

The other details (radiused floor, optimized strakes,...) do help, but are secondary.

Ok, maybe it's high time to update my thread to give a full explanation about the functioning of that diffuser.

BTW: Studing the CFD images, I realised that the diffuser that Variante designed for the last race is far better than any other one (except JJR's that I could not evaluate), it just would need some more air from the front wing to perfectly work. We are going to have much fun next year.

But it looks like yours is producing more downforce! Sure, the bigger and lower rear wing does help, but I think your diffuser is actually more optimized.

Variante has those unique "dive plane" additions...

Honestly those things are there only to quickly produce some more downforce at the front. They actually decrease the efficiency of the car by a good margin.

[AratzH]

I am sure the problem is not from the diffuser. I will take a look later (I writing from the smartphone).

Update: TF images are too small although looking at them with the workstation, but here are my hypothesis.

1) The front wing, chassis shape and the absence of a "counter pressure" (caused by the hx inlets that in TF are located elsewhere) makes all the air from the front wing pass above the car

2) I am not sure, but I think that the external geometry of TF's front wing seems to be designed to seal the sides of the floor instead of feeding them. It would be a good thing (I tried to copy it during the season) if coupled with a geometry that could feed the central part of the floor (ex. high nose), on the contrary (even not my philosophy) Variante's choice to improve airflow from the sides gives better results.

Sorry for the low res images, it wasn't in purpose.
Here are some new pictures (in high resolution I hope).

https://photos.app.goo.gl/h1bdsX5sOORLtDsi1


https://photos.app.goo.gl/PgYussz2EJW2Uav42


https://photos.app.goo.gl/x4GOY8RoMAEHnSNG2


https://photos.app.goo.gl/Iz1PILYjJBHJg2Zl2

They are not exactly the same color scale, but enough to see the difference between Sepang 2016 and LM2017. Actually the outer foot plate is not the responsible for the sealing of the rear diffuser (it was present in both cars with very similar design). I suspect the issue is the vortex that seals the front tire from the front diffuser. It is very effective at sealing the front diffuser, but it keeps flowing under the floor impeding any air to enter from the sides (see the difference in the front tire wakes). I haven't confirmed this yet...

Also very weird how the mid section, that in the LM version is flat all the way from the front, also has low velocity flow at the center of the car....

[CAEdevice]

It looks that all the flow that after running under the front wing, goes above the car and not under the car.

Anyway: congratulations to all the partecipants, the level of this thread is very high, a school of racecar aerodynamics. Thanks to Machin and to everyone.

[machin]

The magic of aerodynamics...

Yes, these images from Aratz really show that small differences in the model can make really big differences to the flow regime... the chances of anyone just copying a model from pictures and getting it to work quickly are very unlikely.

Here are some new pictures

Thanks Aratz.

[machin]

Anyway: congratulations to all the partecipants, the level of this thread is very high, a school of racecar aerodynamics. Thanks ------- to everyone.

Seconded; thanks guys for giving us some great insights into your top-level cars.

[CAEdevice]

I have the suspect that I am revealing too much, but I hope it could help in order to have more competition next year.

Here is a graph showing the air flow from the sides of my car, compared to the flow that comes form the frontal section (I used some simplifications with the "monitoring surfaces" of MFlow, but the results is interesting).

[machin]

Cool. I don't know if it gives too much away; I think it just confirms what the velocity plot was showing; that you have significant (42%) diffuser flow coming from the sides. Thanks for sharing.

[CAEdevice]

Cool. I don't know if it gives too much away; I think it just confirms what the velocity plot was showing; that you have significant (42%) diffuser flow coming from the sides. Thanks for sharing.

I used it during the season to see where the side flow come from.

[machin]

Based on a comment you made a little while back I constructed this graph... it might not be totally accurate, but I think it gives an idea of the sort of work that you guys put in to get your cars to the high performance levels.

[CAEdevice]

Based on a comment you made a little while back I constructed this graph... it might not be totally accurate, but I think it gives an idea of the sort of work that you guys put in to get your cars to the high performance levels.

I confirm that numbers.

Consider that the iterations done during 2017 must be summed with the iterations dome during 2016, because the car is a direct evolution.

[machin]

Among the others, the weak points of my car are:
- side channels of the diffuser (they need to receive more air)
- air behaviour underfloor behind the front wheels

Interestingly the latest issue of Racecar Engineering (Feb 2018), has an article about trying to address both those issues.... They tried a few things, including adding fences from the floor right down to the ground just inside the inner face of the car's tyres (running right from front to back of the car)... this helped the issue at the front (+10% downforce), but with pretty much negligible effect in the rear diffuser side channels... in fact, nothing they did really made a big difference to those diffuser side channels, so they ended up filling them in and that had.... little effect on overall downforce nor drag (positive or negative!)....!!!

The Adrian Newey book has a few sections on the measures that he took to try and improve the flow in this region, including using the exhaust flow and the lower brake duct elements.....

[CAEdevice]

Among the others, the weak points of my car are:
- side channels of the diffuser (they need to receive more air)
- air behaviour underfloor behind the front wheels

Interestingly the latest issue of Racecar Engineering (Feb 2018), has an article about trying to address both those issues.... They tried a few things, including adding fences from the floor right down to the ground just inside the inner face of the car's tyres (running right from front to back of the car)... this helped the issue at the front (+10% downforce), but with pretty much negligible effect in the rear diffuser side channels... in fact, nothing they did really made a big difference to those diffuser side channels, so they ended up filling them in and that had.... little effect on overall downforce nor drag (positive or negative!)....!!!

The Adrian Newey book has a few sections on the measures that he took to try and improve the flow in this region, including using the exhaust flow and the lower brake duct elements.....

Thanks, I am waiting for RE latest issue but I usually receive it after a couple of months.

EDIT: I have just received the RE issue you ere talking about. Very interesting article, but it looks that they did not find a complete solution. They should look at MVRC next edition, maybe someone will find a way to solve the side channels staling.

[johnny comelately]

Fantasic and thank you Machin for starting this thread.
Very instructive and much needed for me.