[KVRC ~ish] CCE LMP01

[RicME85]

My plan was to implement diffuser strakes in the next run.
Looking at your drawing, it would be possible to raise the floor in places so it was like an F1 stepped floor to implement the vortex generators.

I will measure the gap between the underside of the lower rear wing element and the top side of the rear wheel pod on pre-change and post-change models. If the wing is closer to the pod would that have an effect on the increased blue we are seeing?

[machin]

My plan was to implement diffuser strakes in the next run.
Looking at your drawing, it would be possible to raise the floor in places so it was like an F1 stepped floor to implement the vortex generators.

Might be worth trying.. as a separate run from the diffuser strake one, of course!

I will measure the gap between the underside of the lower rear wing element and the top side of the rear wheel pod on pre-change and post-change models. If the wing is closer to the pod would that have an effect on the increased blue we are seeing?

Yeah... proximity to the rear wing will have a big effect ... although the height difference doesn't look that different (difficult to tell for sure on the images though)...???

[RicME85]

Its not to do with proximity, the new wing placement is around 8mm higher from the top surface of the pod than the old one

[machin]

Can you post one of those drag-profile images (the bar chart where it shows where longitudinally the drag is being created)? Just so we can be sure the extra drag is coming from that area of the car, and not some knock-on effect further upstream?

I wonder if the higher wing means that air flow to the wing is better, therefore greater pressure reduction under the wing (as a result of acceleration of the air under the wing and the application of Bernouli) is the reason for the increased drag..???

I guess also the two flat upright surface facing directly backwards behind the wheel fairing (where the wing end-plates attach) is also slightly bigger now that the wheel fairings are taller all the way to the back of the car...?

[RicME85]

The very flat sections at the back of the car where the exhausts exit? They are slightly higher than they were due to the top being flat but not massively.

I will post those graphs shortly as I'm out but IIRC they are almost exact on each of the last 4 runs.

[RicME85]

Test 1




Test 2




Test 3

[wesley123]

The flow in the diffuser area is showing the effects of the entrainment of the rear wheel contact patch wake (I've exaggerated the blue area on the velocity plot for clarity, see below). This low velocity "cloud" spreads out and starts to "take over" the diffuser. I've found that adding diffuser strakes can help to control the spread of that low velocity "cloud" and increase downforce and decrease drag... so this might be something to have a play with amongst others.

I agree here on adding diffuser strakes. However, looking at the image I would suggest running shorter strakes. The bubble that machin explained is a thing that very much exists and I agree on containing it, however, the rest of the airflow is an effect on this bubble. Utilizing the full-length strakes machin suggested you would lack a bit of the expansion as the flow in between the wall and strake follow a "forced" turn. Running a shorter strake would allow you to contain the bubble, but keep the curve that exists in your diffuser.

Alternately, the bubble seems to be caused by the tire, thus reducing the width of the diffuser might help as well, this was a popular application on LMPs in early 00s

[RicME85]

Are you suggesting that I should start the strakes further back (RWCL?) rather than at the start of the diffuser?

[LVDH]

Very impressive improvements, esp. as they come through a forum in the internet.

... One easy fix will be to have the sections infront of the front wheels flat (and as low as possible).

I am pretty sure that that will generate some free downforce.

[RicME85]

That will come, every model with that change I had tried running previously OCCFD ended early with divergence but that wasnt run on the stable setting as Matteo suggested recently.

[wesley123]

Are you suggesting that I should start the strakes further back (RWCL?) rather than at the start of the diffuser?

Let them start from the start of the diffuser(although letting the strakes start a bit later would be interesting as well) but let them end sooner instead of continuing them to the trailing edge.

[machin]

...They are almost exact on each of the last 4 runs.

For now I would be inclined to go back to the previous rear wheel fairings and wing end plates... It is likely that a combination of all of the little changes added up to the total drag increase and in real terms they gave a negligable increase to downforce....

[RicME85]

What does the last run with the old wing and fairings look like in Stopwatch compared to the third test I posted last night?

[machin]

Probably best to look at 3 runs, and only fair if I only present the VSW Test Track figures rather than any of the official race tracks which other competitors can't access:

• Original "good" car with the original wheel fairings, wing end plates and front suspension fairings: 41.7 seconds
• Modified car with new wheel fairings ("Test 1"): 41.9 seconds (+0.2 seconds compared to previous)
• Modified car with new wheel fairings and Modified front suspension fairings ("Test 3"): 41.76 seconds (-0.14 seconds compared to previous)

So I think you'll be better off with the original rear wheel fairings but with the modified front suspension fairings... this potentially might give you a lap time of 41.56 seconds (41.7-0.14 = 41.56)... however, what we don't know is that maybe the modified front suspension and original lower rear wing may work less well together than the original configuration....!!!

That leads me to think that the safest way to proceed is to do one change, get the result, decide if it is better or not: if it is better then try another modification using the new car as the basis... if it is not better go back and use the previous car as the basis for the new modification... that way you don't lead yourself down a blind alley...

[machin]

Let them start from the start of the diffuser but let them end sooner instead of continuing them to the trailing edge.

... One easy fix will be to have the sections in front of the front wheels flat (and as low as possible).

I've just drawn these two modifications for clarity for any casual readers who might not be able to follow the thread...



Although I must admit I've never seen diffuser strakes on a real car end half way along the diffuser... and I've never tried them in CFD myself as a result....