Aero Function of the Floor

[hardingfv32]

I think I appreciate the how the the generation of down-force by the floor has been generally portrayed. The flow velocity is increase and low pressure generated. I am disregarding the rear diffuser assembly for this discuss. Just discussing the operation of the floor in isolation from the rear diffuser IF possible.

With the current 2-3 degree floor rake of most cars, the floor looks like a diffuser with the volume constantly expanding from the leading edge to the rear diffuser assembly. There is almost no funnel at the front to force flow under the splitter. Looks like the splitter directs most flow above the floor entrance. Just the chamfer on the plank and maybe 15 mm ground clearance to let air under the floor. No apparent nozzle.

So how does the underside of the floor function as an aero application?

Brian

[rough_wood]

A common missconception is that the flow is compressed. The flow is not compressed from both a technical standpoint, and from the standpoint you may be thinking of.

First of all, think about compressing something. What it does is increases the pressure, which is not what you want to do on the underside of the car! You want to sort of decompress the air, and to do this you want to speed up the air. You do this by conserving the mass flow rate under the car, decreasing the cross sectional area the flow can traverse, and then by necessity the flow will speed up in order to follow the conservation of mass.

Really the underside of the floor functions more as a Venturi. If you would like, I can answer this in more detail.

[hardingfv32]

I correct my statement to remove the word compression.

I understand the desire to use the venturi example, but how does the fit with how we know the floor is shaped and positioned (rake)?

Is the current raked flat floor/plank with a roughly a 5 mm radius at the very front good enough to be an effective venturi opening (nozzle)? There are some critical shape requirements for an effective venturi when all is said and done. Is this the case that something is better than nothing?

Brian

[shelly]

I repost here my picture




It is a mspaint sketch of a floor in bottom view, colored with cp - pressure coefficient. It is not detailed nor precise, but I think it summarizes a lot of things, even if it has to be taken with a pinch of salt.


We can see the general low pressure that acts on the floor and the lower pressure zones due to radiuses and vortices - which are visible via their low pressure trace.

I think there is a lot to discuss starting form this image

[hardingfv32]

I saw your image posted earlier. This mainly represents the side pod floor, is that correct? In general except for the ground clearance aspect it would seem useful. Looking at the image it would seem the big pressure reduction numbers are at the very front of the floor. Off coarse I am just talking about the floor.

The one thing that makes me nervous about your image is the vortex activities. I am think the vortex activity is much more limited at the front of the splitter that is 15 mm from the track surface.

Brian

[marekk]

The one thing that makes me nervous about your image is the vortex activities. I am think the vortex activity is much more limited at the front of the splitter that is 15 mm from the track surface.

Brian

Can't see anything wrong in vortex cores with less then 15 mm of diameter in this place. That's about the number i would expect.
That said, i don'r really understand how they manage to keep the cores near the ground, when all the flows form FW go up.

[shelly]

@brian> under the sidepod the floor clearance is at least 60mm

@marekk> the vortex are generated by ttray, bargboard, diffuser fin, diffuser footplate

[marekk]

@brian> under the sidepod the floor clearance is at least 60mm

@marekk> the vortex are generated by ttray, bargboard, diffuser fin, diffuser footplate

And FW elements. At those speeds ballpark figure for vortex core would be around 5-6% of generating elements chord - so les then 15mm is perfect for me.
I've posted some time ago in other thread pictures with vortexes under the floor, so no problem with beliving there is enough space:-)

Back to original question.
At 2-3 degree rake it's just a wing with negative AoA. Barn door type, very low apect ratio, highly inefficient due to bodywork, but wing anyway. With added curvature at leading edge has to produce some downforce (and drag).

[atanatizante]

I would like to ask you guys which have better aerodynamics knowledge than me if it could be utilized the Coanda effect on a F1 car? Maybe diffuser is one place?

[hardingfv32]

1) So we are talking an inverted wing in ground effect. There is some research on that topic that can be reviewed.

2) So I assume reducing the size of opening at the leading edge (ground clearance) has a limit as far as the floor's performance. The boundary layers become an issue?

IF vortices are directed at the front of the floor how does this help? Can they help get more flow under the leading edge? Interact with the boundary layers?

Brian

[shelly]

@marekk: can you retrieve the picture of the floor?
I agree with you on the inverted wing (told you so in another forum some time ago).
The vortex from the front wing are not the most important under the floor: bargeboard and ttray are the main vortex generators for the front floor.

@brian: look at my picture: the voritces that go under the floor directly produce downforce, because the low pressure of their core acts against the flat floor.
I represented this effect with the blue longitudinal streaks. The other two transversal blue streaks are the front and rear suction peaks on the curvature radii of the leading edge and kink line.

[machin]

This from a 2009 double diffuser CAD model that was put through CFD:-



It confirms that the most downforce (low pressure) is generated at the "kink" line in the diffuser.

I don't have any barge boards on this model, so no real vortex generating bodywork... but one thing always confuses me about the talk of vortexs and underfloor pressure:- If the core of the Vortex is directed at the leading edge of the floor, won't it equally act on the upper and lower surfaces until it dissipates?

I'm having trouble visualising it....

[shelly]

The vortex gets squeezed under the floor, it acts only on the lower surface of the floor.
in your picture front downforce production is also visible, even if the suction peak is not strong

[machin]

Another question if I may: if the vortex core is lower than normal atomsphere is the outer edge higher than atmosphere?

If 'yes', doesn't it also impact on the underside of the floor?

Cheers!

[Just_a_fan]

Another question if I may: if the vortex core is lower than normal atomsphere is the outer edge higher than atmosphere?

If 'yes', doesn't it also impact on the underside of the floor?

Cheers!

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