Yeah, I've been thinking of these "double inflection diffusers" (of which this is just an extreme example) in terms of velocity and momentum: where the velocity is highest (where the floor is closer to the ground) accelerating the air away from the ground (creating downforce) creates a larger momentum change than where the velocity is lowest and the air accelerates back towards the ground (the "arch" part), which must produce some lift. Hence net vertical force in the diffuser region is in the downward direction.variante wrote:Beautiful article, Mantium. Thank you for sharing.
About your diffuser: I think the reason why it works could be found in the compression/decompression process and its ground effect interactions. As the incoming air approaches the diffuser's "protuberance" it slows down in its compression stage, far away from the ground; energy "recovery" is fullfilled during the decompression stage, near to the ground. It should be also noticed that the pressure differential generally reaches higher values during the decompression phase. As a third observation, in a well designed geometry potential energy of the compression phase can be stored mostly in form of drag (instead of lift) and released in form of downforce.
I think that your current design lacks a little bit of the optimization to fully take advantage of this last point. Still it looks very promising.
A similar device is the "pelican nose" pioneered by Lotus. I believe it works in the very same way.
That was the plan for this year.julien.decharentenay wrote:@mantium It looks like you will be a serious competitor if you are going down the automated optimisation path.
Yes, I do. Adjoint is very tricky, though. I used to work with a quite good adjoint solver. Besides the big challenge of obtaining good results you have to be able to use them. Normally you run into the big problem of manufacturing. Here we are mainly constrained by the rules. CAESES is actually able to read adjoint sensitivities and use them for the geometry modification while also obeying constraints. So maybe that would be the way to go for this competition.julien.decharentenay wrote: Any experience with adjoint solver?
Same here. Earlier this year I was working on a process using SU². I hope I will have some time later this year. Next year I might be able to show some results on the car.julien.decharentenay wrote:It was one my plan for this year - but did not get the time.
OK, sounds like I did not invent anything new (as always). Could you point me to some examples or even papers?machin wrote:Yeah, I've been thinking of these "double inflection diffusers" (of which this is just an extreme example)...
I am more than happy to investigate how this thing works. Maybe we could do that as a community in the forum? That way I would not have to do all the work alone.machin wrote:If you had freedom in the rules, I was wondering if you could design a complete floor with a "wavy bottom" (!!!!), so you'd end up with a series of low pressure peaks along the whole floor and not just at the inlet and exit? Presumably at some point there would be too much pressure loss and air would start to avoid going under the floor and take some easier route instead... But that would be down to selection of the optimum "waviness" (in terms of number of waves and their radius of curvature in both the "throat" and "arch" areas).
It does sound very interesting... Can you give us a brief run-down on how the automatic optimisation works?LVDH wrote:That was the plan for this year.julien.decharentenay wrote:@mantium It looks like you will be a serious competitor if you are going down the automated optimisation path.
Yeah, I thought it probably wouldn't be possible within the rules (I really should make myself more familiar with them!)RicME85 wrote:With regards to the full length wavy bottom idea....it would be only possible in a section to the outer edge of the floor.
There are many ways of parametrizing geometries. And this is by far the most difficult part using design space exploration or optimization techniques.machin wrote: It does sound very interesting... Can you give us a brief run-down on how the automatic optimisation works?
While I always wanted a device with my name I propose "Mantium Diffuser".machin wrote:(I think LVDH (as the inventor) should come up with a name for the arrangement as "double diffuser" has been used before!)