Parametric Racecar Aerokit design [MVRC]

[machin]

Just 70-80 more CFD runs to go and I'll be there! Assuming I don't go down any wrong development paths along the way!

First a question for you Variante:

...thanks to vortices that are counter-rotating to those that are closer to the wheels....

What feature(s) should we look for on the CFD images that would tell us where the vortices are and what direction they are rotating in?

A dark blue circular region in a cross-section slice showing total pressure, I presume? How about direction?

[variante]

What feature(s) should we look for on the CFD images that would tell us where the vortices are and what direction they are rotating in?

Stronger vortices are recognizable thanks to their white or blu color (talking about pressure images, with the given color scale), coming in the shape of a slim and elongated thing along the surfaces of the car. The weaker ones need a different color scale to be detected.
The direction of rotation is a deduction...sometimes it is obvious, sometimes it is not. In fact, I'm not sure about CAEdevice's inner ones.


The best way to study vortices interactions in the most complex systems is to download ParaView 5.1.2, open the CFD case, and use the SurfaceLIC plugin on a slicing surface. Here is an example that CAEdevice publishes a while ago:

[CAEdevice]

The vortices of the central region rotate in the opposite direction in my car but I have difficulties to genereate a surfaceLIC plot with the 2017 data (Variante is right).

[machin]

So, a couple more CFD images.... The MVRC results give you the breakdown of forces on the various body parts... so I constructed the image below to give a visual representation....



Clearly the downforce distribution is way too far back.... and compare to the Monaco version of CAEDevice's car from 2016 (a very similar car layout and good for comparison):-



Clearly this car is creating a lot more downforce at both ends, particularly the front. The initial conclusion might be that CAE Device's Monaco Car simply has a much bigger front wing/diffuser (it does)... but interrogation of the surface flow on my car's front wing shows that a large proportion if it simply isn't working (note sudden loss of velocity)



So the next step is to get that surface (and the rear diffuser) working much better...

[CAEdevice]

Very good job Richard.

I think that your front wing is very near to its maximum performance. For Monaco 2017 (about the same layout) I added a second front wing above the original one. It was highly inefficient, but it added a little amount of downforce that helped in a track where efficiency is not important (I don't like extreme df tracks).

[machin]

I think that your front wing is very near to its maximum performance.

Interesting... My assessment was that the sudden change from high velocity to low/no velocity indicated flow separating part way along the wing... Would you say otherwise?

[CAEdevice]

I think that your front wing is very near to its maximum performance.

Interesting... My assessment was that the sudden change from high velocity to low/no velocity indicated flow separating part way along the wing... Would you say otherwise?

Yes it is partially caused by "classical" flow separation and partially by the presence of a slightly higher pressure region in front of the hx inlets.

I fear I am revealing too much, but I obtainded more front dowforce just increasing the flow through the hx (that is the reason I use airfoils above the rear suspension and why hx flow was often a bit above the minimum required)

[AratzH]

This is such an interesting thread. Despite my poor performance this year I would aslo like to share some colorfull pictures.


Pretty clear where the problem is... Also interesting to note that my front "diffuser" seems to be working even harder than Mateo's! Totally useless without something in the rear to compensate
I'm looking forward to next year's rules to see where to take my design.

[CAEdevice]

This is such an interesting thread. Despite my poor performance this year I would aslo like to share some colorfull pictures.
https://thumb.ibb.co/b0f596/TF_Le_Mans_ ... Cp_007.png
https://thumb.ibb.co/iLehp6/TF_Le_Mans_ ... ll_007.png
Pretty clear where the problem is... Also interesting to note that my front "diffuser" seems to be working even harder than Mateo's! Totally useless without something in the rear to compensate
I'm looking forward to next year's rules to see where to take my design.

Thanks for sharing!

Your front wing is working much better than mine, but it looks you don't have enough air in the central region of the rear diffuser. The air entering from the sides is about the same of my car, but much less than Variante's car, who chose a different philosophy.

[rjsa]

This is such an interesting thread. Despite my poor performance this year I would aslo like to share some colorfull pictures.
https://thumb.ibb.co/b0f596/TF_Le_Mans_ ... Cp_007.png
https://thumb.ibb.co/iLehp6/TF_Le_Mans_ ... ll_007.png


Pretty clear where the problem is... Also interesting to note that my front "diffuser" seems to be working even harder than Mateo's! Totally useless without something in the rear to compensate
I'm looking forward to next year's rules to see where to take my design.

That happened to me with the 2ndd order calculation introduction and also on the first 1 or 2 software updates. Every time it was due to a stalled RW.

[machin]

The air entering from the sides is about the same of my car....

You think? Again, I think you are being modest; I think it is much less on Aratz's car; there is mainly green and a tiny corner of red in front of the rear wheel fairing on the floor in the velocity plot (left image) indicating low flow....


Whereas your car has huge red/pink triangles in that area on the velocity plot (left image again) showing very high velocity into the diffuser from the space in front of the rear wheel fairing:-



Aratz's diffuser seems to be barely pulling any air through from the sides... even compared to my car, which has the two red streaks on each side of the floor:-



Aratz's result is very intriguing....

[CAEdevice]

I was not modest (or just a bit), I was talking about my low nose version. The high nose version works in a different way (if I reduce the air from the sides it improves).

I was wondering if TF considered to change the front in order to feed the diffuser.

[machin]

I was wondering if TF considered to change the front in order to feed the diffuser.

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....

[CAEdevice]

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.

[CAEdevice]

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.