Single seater diffuser profile help

[marcush.]

As I understand the difusser can never be looked at without the floor and everything in front of it.
so if you happen to starve the floor already (by scraping the ground with the leading edge of the floor -don´t hope for being able to fill a steep diffuser .
I learned you should have a decent curve -around r80 mmradius at the transition from flat floor to difusser to avoid separation and the possible angle of difusser is depending on the airflow thats available...you maybe able to get an reflex curve working with the difusser .but that needs very good sealing and perect detail in workmanship for the floor itself...

your 55mm rigehight at difusser start is that static or dynamic height?

[mep]

From common sense I say that a vortex is usually not a good think. In your case it is not just preventing downforce, it is generating drag so you should try to avoid it. However this picture is not really a representation of a formula type diffuser because usually it is just a thin plate. This means that there is air flowing over the diffuser and this can minimise the vortex generated there. Not just that but the airflow over the diffuser can also help to suck the flow going under it slightly up and therefore keep it attached. To help increase this effect teams mound a airfoil (beam wing) over the diffuser. Important here is the interaction between those parts.
Regarding your videos:
First of all really cool work and thanks for uploading them here.
In the videos you can see that the flow stays attached at the first line of fibres (counting stream wise, from the front of the car). The third row is quite detached and the middle row is something like a transition area. Maybe you start to extend the diffuser tangential from the transition area instead of bending it further up. You might get less downforce at high speed where your flow stays attached but gain it at low speed (corners)
Interesting is also that during cornering some of the fibres get dragged under the vertical plate which shows that there is some cross flow.

[gato azul]

maybe you find this a worthwhile read.

On a side note, maybe you want to mind about an alternative fixing method for your strakes (vertical fins) in the diffuser.
If space permits it ( and I don't know, because can't see the top of the diffuser), you could mind about using
slots in the diffuser top/roof and fix the strakes on top with a lateral bolt or rivet, that would clean up the
air flow quite a bit, and you may see less flow separation where you don't want it.

Good luck

[nacnac]

Answering a few points

The static rear ride height was set around 65 mm for this test. The front around 45mm (I am restricted to a minimum 40mm ride height). I may well try and change the flow under the car from the front, this is obviously key.

I can't really change the diffuser construction much, possibly I could use counter sunk rivets the other way around but I'm not sure how much I fancy drilling them all out!

I thought it interesting how the wool tuft in the top left corner amongst the rivets always remains attached. I will next try controlling the flow in front of the rear wheels better. Perhaps I will put the results up again.

Edit: I had already found that link and have read the article, thanks though.