[MVRC] Mantium Virtual Racecar Challenge 2018

[variante]

Super interesting comparison! JJR is missing tho...

Yeah, very different diffusers.
- Yours is clearly better around the center, as you are pumping much more air throught the Front Wing.
- I might have an advantage on the outboard areas, and also just after the transition edge (between flat floor and diffuser), probably because mine is less sharp than yours.
- After that, your diffuser retains the low pressure much better than mine, maybe because vortices can easily keep contact with the surface (without my abrupt upward kick) and also because of your big and well functioning Beam Wings.

Cool to see, also, that the Leading Edges of the flat floors have a similar shape (incidentally, i guess, since they work differently).

[etsmc]

The diffuser is somewhere i struggle to understand, how much should air speed change should it be faster at the exit of the diffuser than the air over the top or vise versa? How much turbulance is acceptable?
My rear wing profiles havent changed in the last 2 years and my diffuser i think the only changes this year has been to the strakes since its initial design.

The back of the car has been neglected in development but only because as always front downforce was hard to produce and keep the car balanced.

[machin]

Matteo, you make a good point; now that all cars are submitted and it is the end of the season, and indeed the end of our “LMP” era, there are no excuses not to show some nice details about your cars.

Following on from Variante’s comments I would particularly like to see a detailed comparison of ETSMC’s diffuser profile compared to one of the top cars (Variante, CAEdevice, JJR)....

[etsmc]

Im happy to play along with that. Just name the post processing image filename and i will upload it.

[CAEdevice]

- After that, your diffuser retains the low pressure much better than mine, maybe because vortices can easily keep contact with the surface (without my abrupt upward kick) and also because of your big and well functioning Beam Wings.

It is 100% an effect of the vortices, the beam wing actually works badly. I changed it 8 times in 10 simulations without being able to optimize it. I am conviced that my diffuser side channels flow suffers with the "shadow" of the front wheels (maybe some side flow could be useful to reduce this effect: I would need another year of developement with LMPx to be sure...).

[variante]

the beam wing actually works badly. I changed it 8 times in 10 simulations without being able to optimize it.

Ok, but you should see mine, which gets very slow and dirty air (also due to the Front Wing extension). Mine is also much smaller, as the diffuser leaves it no space.

I am conviced that my diffuser side channels flow suffers with the "shadow" of the front wheels (maybe some side flow could be useful to reduce this effect

Having the opposite problem, I tried to force more air through the ceter, but it was terrible. The airflow angles decreased and wheel wake ended inside the most sensitive diffuser areas (instead of going toward the center of the car).

I would particularly like to see a detailed comparison of ETSMC’s diffuser profile compared to one of the top cars

I'm a bit shy about showing the actual schematics, but I can tell you it's nothing complex... Just a concave arch ending under the suspensions (start: 25°; end: 0°), then a straight line, then a convex arch pointing to the sky (variable angle). The transition between the flat floor and the first arch is not sharp at all.
The exact shape must change depending on the airflow amount, quality and angle. So i want to tell etsmc: try different diffusers, starting with conservative shapes and angles; modify other parts of the car (on the front) to increase airflow amount and quality; modify the diffuser; repeat. At each step, observe how the flow behaves (where the wheel wake goes, how strong the vortices are,...).
My diffuser is not so optimized, and anyway it would not work on Mercury's car right away, for the mentioned reasons.

[etsmc]

Well, I picked the [casename]-005_U_-012 image as it seemed to be the only slice that didn't have a diffuser strake nearby that interrupted the profile of the diffuser. just for comparison sake, I run 30 slices on each axis in the post-processing settings.

I didn't think this shape would be too aggressive but maybe because I was trying to use the max height at the diffuser exit there is too much room for expansion and not enough flow?

[variante]

Looks like the first kick is at 30°. As i said, i use 25°. Doesn't mean that 30° doesn't work, but you need to make sure that the airflow is well energized. Try with 15°, then 20°,...

The last kick should be upwards (convex shape) to maximize expansion outside the diffuser, or neutral (straight-ish and quite horizontal) to keep vortices attached, but yours seems to be concave.

Overall it looks good, so i think the main problem is how well it is fed. Studying the airflow velocity map on the bodywork would help.

Finally, let's not forget the importance of (controlled) vortices. That goes beyond the 2D study, and depends on the Strakes design. The stronger the vortices, the more aggressive the diffuser can be.

[etsmc]

Looks like the first kick is at 30°. As i said, i use 25°. Doesn't mean that 30° doesn't work, but you need to make sure that the airflow is well energized. Try with 15°, then 20°,...

The last kick should be upwards (convex shape) to maximize expansion outside the diffuser, or neutral (straight-ish and quite horizontal) to keep vortices attached, but yours seems to be concave.

Overall it looks good, so i think the main problem is how well it is fed. Studying the airflow velocity map on the bodywork would help.

Finally, let's not forget the importance of (controlled) vortices. That goes beyond the 2D study, and depends on the Strakes design. The stronger the vortices, the more aggressive the diffuser can be.

Thanks for the tips.

I thought this was just going to be a show and tell and the development of my car was finished but now thanks to Variante I have just made a change and started a new case...

My diffuser first kick was only 21°so I have brought it down 13° kept it running at a shallower angle then kick up near the exit...

Anything else people would like to see?? wings, wing profiles suspension covers?

[Alonso Fan]

Looks like the first kick is at 30°. As i said, i use 25°. Doesn't mean that 30° doesn't work, but you need to make sure that the airflow is well energized. Try with 15°, then 20°,...

The last kick should be upwards (convex shape) to maximize expansion outside the diffuser, or neutral (straight-ish and quite horizontal) to keep vortices attached, but yours seems to be concave.

Overall it looks good, so i think the main problem is how well it is fed. Studying the airflow velocity map on the bodywork would help.

Finally, let's not forget the importance of (controlled) vortices. That goes beyond the 2D study, and depends on the Strakes design. The stronger the vortices, the more aggressive the diffuser can be.

Thanks for the tips.

I thought this was just going to be a show and tell and the development of my car was finished but now thanks to Variante I have just made a change and started a new case...

My diffuser first kick was only 21°so I have brought it down 13° kept it running at a shallower angle then kick up near the exit...

Anything else people would like to see?? wings, wing profiles suspension covers?

Front and rear wing profiles please.

I could do with some pointers

[variante]

My diffuser first kick was only 21°

I did not mean the chord angle, but the angle of tangent to the first point of your ramp (fillet excluded). I've measured yours, and it is something like 28° or 30°. Mine is 25°. The chord angle is a different and less controllable parameter, from my point of view.

Anything else people would like to see?? wings, wing profiles suspension covers?

Velocity map of the undertray (view from below/behind, possibly).

[LVDH]

Anything else people would like to see?? wings, wing profiles suspension covers?

A simulation with the rear wing much closer to the trailing edge of the diffuser.

[Ft5fTL]

Since everyone is sending some post processing images, i felt i should send some images from the car that i send for the last race:

[etsmc]

Sorry guys had to go away for a couple of days so wont get the results of the diffuser test till Wednesday.
If LVDH wants to post some of the requested images of my car its fine to show the latest images if they are ready from the pukes peak race.
Once i get back i will run a simulation with the rear wing lower.

Nice design from pure power the channel under the nose down to the floor looks interesting.

[variante]

Yeah, PurePower, that looks good. Maybe less upwash and thicker airfoils to help the Rear Wing.

Interesting use of the Mantium Diffuser. I never managed to study it properly.

@LVDH will we see the results tomorrow?