Aero Function of the Floor

[hardingfv32]

Shelly

I appreciate what you are illustrating, but it only represent your belief of what the vortices are doing.

I am with Machin, I still don't understand how a vortex at the inlet/leading edge help. I appreciate the low pressure and/or sealing benefits of vortices on the sides, but are these desired at the inlet?

Also, can you think of any machine/system that might operate with vortices under similar conditions. I need something to feed my searches about using the low pressure core of a vortex and I am drawing a blank.

Brian

[machin]

Does anyone here have any cfd plots showing these vortices acting on the floor?

[hardingfv32]

Wouldn't the outer edge of the vortex be at or just less than the local ambient?[/quote]

I think you are correct.

If we route the vortex under the floor would we not expect to only see the pressures on the perimeter of the vortex? It is a system and if we try to access the core wouldn't the vortex terminate?

Brian

[hardingfv32]

Does anyone here have any cfd plots showing these vortices acting on the floor?

I have not found any studies or articles on the subject, but then I would not expect much directly on point.

We need to find some other field of study, mechanism, or system that is more common that uses vortices in a "somewhat" similar manner and extrapolate from that informations.

Any ideas?

Brian

[Just_a_fan]

Wouldn't the outer edge of the vortex be at or just less than the local ambient?

I think you are correct.

If we route the vortex under the floor would we not expect to only see the pressures on the perimeter of the vortex? It is a system and if we try to access the core wouldn't the vortex terminate?

Brian[/quote]
But if the vortex is at a lower pressure than the flow around it, it will act to seal the main part of the floor from flow that might otherwise want to enter from the sides e.g. "dirty" air from the tyres, edge of the floor etc. The vortex itself wouldn't be generating large increases in downforce directly but it would be allowing the rest of the system to work more efficiently.

[hardingfv32]

"But if the vortex is at a lower pressure than the flow around it, it will act to seal the main part of the floor from flow that might otherwise want to enter from the sides e.g. "dirty" air from the tyres, edge of the floor etc. The vortex itself wouldn't be generating large increases in downforce directly but it would be allowing the rest of the system to work more efficiently."

Yes, I agree.... but the question is, what happens when we apply those same vortex benefits to the entrance of the floor/floor inlet?

Brian

[shelly]

I post now a quick answer to some of the issues emrged /i will try to be more complete later.
Examples of vortex acting against a surface to make force are delta wings or jet fighter strakes. The difference is that with a delta is the outer edge of the wing creating the vortex, whereas with a f1 front floor vortices are generated by the ttray and bargeboard and then go under the floor

[Just_a_fan]

It's all about energy and preventing separation of the flow. On an aircraft wing, the vortices are used to delay separation of the flow. In a ground effect situation, the development of flow separation is likely to lead to choking of the flow below the vehicle. By delaying seaparation one reduces boundary layer depth. Once the diffuser starts to affect the flow, separation is reduced (unless it occurs in the diffuser itself). Or not?

[hardingfv32]

Being very precise and discussing only the leading edge of the floor with about 15 mm ground clearance:

A) I want vortices laced flow entering the gap below the leading edge?

B) I want the leading edge to generate vortices in the flow entering the gap below the leading edge?

If I am NOT concern with flow separation do I want vortices before or after the inlet?

Brian

[allstaruk08]

hello people i have a small understanding of aerodynamics but if you have vortices laced flow entering the gap below the leading edge, on the R31 wouldn't the exhaust gases get in the way of the vortices massively ?? the exhaust pretty much blows along the whole leading edges each side of the plank.

[MIKEY_!]

allstar: There's several other threads for that one mate. (it's a lot of reading, good luck)

I am under the impression that the vortex not only helps with flow separation but the faster moving air of the vortex will create the desired DF through Bernoulli's principle.

[hardingfv32]

allstar: There's several other threads for that one mate. (it's a lot of reading, good luck)

I am under the impression that the vortex not only helps with flow separation but the faster moving air of the vortex will create the desired DF through Bernoulli's principle.

Please explain your impression. What direction is the "faster moving air of the vortex" traveling at: circular in true vortex fashion or in line with the normal air flow trajectory?

Brian

[MIKEY_!]

I think the idea is that that though the vortex air flow is moving rearward at the same speed as the regular flow the vortex also has it's circular (rotational) flow which means overall it is faster moving.

[hardingfv32]

I think I am appreciating that the vortices can generate low pressure after some delta wing research.

Does that mean our goal is to get as many vortices under the side pod floors and central floor as possible? Maybe under all aero systems on the car?

Is flow under the central floor leading edge require other than to produce vortices?

Brian

[shelly]

@just a fan: strakes on fighters are high aoa devices. In a certain sense they prevent separtation - but they porduce lift, the so called vortex lift.

In f1 they are after vortex downforce. The vortex has a very low pressure (related to crntripetale acceleration to force air along a curved helical path). If you get a vortex to run unedr a downfacing surface you get downforce directly, in the same way as you get lift on strakes or delta wing.

Then as mikey says, if you increase the velocity of the vortex along its axis you strech and narrow the vortex tube; there is a theorem by helmoltz that says that says that this will increase the vorticity (conservation of angular momentum, like a ice skater that accelerates her rotation when closes the arms). That's why I think the ebd is so effective, because it accelerates an existing vortex. Also the leadinf edge vortices are accelerated by the accelartion around the leading edge.

So if you manage to accelerate the vortex, you get a narrower vortex and a even lower pressure peak. The influence of low pressure peaks is local.

So from a certain point of view, the more vortices under the floor the batter; the problem is that vortices are very dissipative and introduce a loss of energy in the flow. So too many vortices is bad; it's a compromise I think.

There are some vortices that are let's say "unavoidable" feature of the flow: once they are generated, why not exploit them? But generating a lot of vortices aiming for downforce is not very efficient.

We can see one nice example of "unavoidable" on the rebull last front wing: at the transition between the mandated central wing section and the outer part of the wing there is a vortex, because the two adjacent section are very different in size and generate different loading; thus rbr have chosen to make a small rounde curl on the mainplane to house that vortex, take a gain in downforce from its low pressure before it is released downstream.