Lotus E21 Renault

[Blackout]

by http://www.flickr.com/photos/allmotorsport/

[kilcoo316]

There is something worth noting in the above photograph for any amateur aerodynamicist out there.


Just how little the teams care about drag and conversely how much they care about downforce.

[bhall]

What specifically makes you say that? I mean, I know you know what you're talking about. I'm just confused.

Isn't efficiency paramount? Otherwise, what prevents teams from just cranking up the angles of attack on the front and rear wings and leaving it at that?

[kilcoo316]

Otherwise, what prevents teams from just cranking up the angles of attack on the front and rear wings and leaving it at that?

The rear wing would stall and while the front wing wouldn't quite so quickly, the aero balance would be out.

[kilcoo316]

What specifically makes you say that?

The bargeboard is a multi-element wing producing nothing but drag
- or forces towards the outside of the corner.



[well, it also creates downstream effects - but leaving that aside for a moment ]

[raymondu999]

Wouldn't the centripetal effects provided by the sidewrds "lift" be counteracted by the other bargeboard though?

[bhall]

What specifically makes you say that?

The bargeboard is a multi-element wing producing nothing but drag
- or forces towards the outside of the corner.



[well, it also creates downstream effects - but leaving that aside for a moment ]

I think those downstream effects are pretty important, yanno? There's no reason to create drag just to create drag.



For me, it looks like a more efficient use of the space in which bargeboards are permitted. By rule, they're largely confined to an area in front of the sidepods, which means, by default, they have a pretty high AoA, one that would seem to cause airflow along the rear of the bargeboard to separate if the bargeboard is too big.

Ferrari, for one, shortens the "span" - does that word still apply here? - where the AoA is highest and appears to rely on vortex generators to continue to move airflow outward. The Lotus solution seems far more elegant in that regard.



Moreover, don't slotted wings produce less drag than their solid counterparts?

Happy as hell to be educated here.

[kilcoo316]

Wouldn't the centripetal effects provided by the sidewrds "lift" be counteracted by the other bargeboard though?

Not in yaw (when it would actually matter).

Indeed, both bargeboards would likely be producing outward forces through somewhere like Becketts where yaw rates are astronomically high.

[kilcoo316]

I think those downstream effects are pretty important, yanno? There's no reason to create drag just to create drag.

They are taking the drag hit for further downforce due to the wake - hence my point on the relative importance of downforce compared to drag.

by default, they have a pretty high AoA, one that would seem to cause airflow along the rear of the bargeboard to separate if the bargeboard is too big.

Yep, but multi-elements offset flow detachment.

Moreover, don't slotted wings produce less drag than their solid counterparts?

No, but they do produce far more lift.

However, in this case, the "lift" is directed mostly backwards, so has the effective of being drag!

[bhall]

Right, so to mitigate the huge drag penalty that would otherwise be caused by the face of the sidepods were there no bargeboards at all, Lotus has bargeboards that, like all bargeboards, move airflow over them outward, and, because they're slotted, also move airflow behind them outward. They're able to do the latter, because, as you've said, the slots prevent that airflow from separating, which would ordinarily occur without slots due to the high AoA of the bargeboards. (Is my understanding more or less correct here?)

Naturally, the bargeboards produce drag, just like anything else, but it's not nearly as much drag as would be produced if free stream airflow was allowed to smack the face of the sidepods unguarded, plus there's downforce to be made downstream with the air they move, both of which are why all teams employ them to some degree.

At any rate, that's why I see the slotted bargeboards as a more efficient use of a necessary evil.

(I sincerely hope this doesn't seem argumentative. An incessant desire for clarity is one of my vices.)

[shelly]

I would not put reducing drag against teh sidepod in the group of the main functions of bargeboards.One should not think, like newton did, that air impacts against surfaces: that happens only in hypersonic flows (sin squared drag law).

In our context: tha bargeboard are flow conditioners whose primary function is probably making the front wheel wake interaction with the rest of the car weaker, by moving towards tha outside. they guide the flow around the sidepod with the help of the pod wing, give a better flow to the floor leading edge.

The bargeboard also produce two vortices, upper and lower. The upper one rolls around the sidepod in the undercut zone (we discussed it a bit above in the thread), the lower one goes on the floor leading edge, gets accelerated and flow under the floor, and then flows under the floor thus producing downforce. Significant that the team that worked on enhancing this vortex in 2011 with the forward exiting exhaust is the one using now a slotted bargeboard

[kilcoo316]

Naturally, the bargeboards produce drag, just like anything else, but it's not nearly as much drag as would be produced if free stream airflow was allowed to smack the face of the sidepods unguarded

I would say that statement is completely incorrect.

As shelly alludes to, you are thinking hypersonics (Newtonian) and not subsonics.


The radiator will have a pressure drop across it which, combined with the rad ducting geometry will determine how much massflow passes through the sidepod at any given speed/air temp - the rest will know by the pressure perturbations back upstream to divert around the sidepod. Clever design around the sidepod inlet can lead to local thrust being produced.


Again, as shelly points out, the bargeboard is there for the benefit of the floor/diffuser. Both by its immediate wake effects and by keeping the size of the chaotic turbulent eddies within the spillage flow around the sidepod inlet to a minimum.

[bhall]

Actually, I was thinking about the "face" of the sidepod as being the area underneath the inlet. That may or may not change change views on what I've said here. But, it is what I meant nonetheless. (I do not possess a degree in engineering, nor am I mechanically inclined. You can tell, huh? One of these days, though, my internal vocabulary will match real life nomenclature.)

[...]

Bargeboards play a key role in directing the flow around the front of the car, [they] effectively route the flow between the front wheels around the car, flow inside (green) of the boards is routed into the sidepod intakes and around the outside of the sidepods, while the dirtier flow (brown) on the outside of the bargeboards is kept clear of critical aerodynamic surfaces. This shaping of the flow inside the barge boards helps the flow negotiate the tricky interface between the step and sidepods.

Either way, I can see that my "knowledge" is incomplete here. Thanks, guys. +1s all around. (Don't spend it all in one place.)

[...]

The radiator will have a pressure drop across it which, combined with the rad ducting geometry will determine how much massflow passes through the sidepod at any given speed/air temp - the rest will know by the pressure perturbations back upstream to divert around the sidepod. Clever design around the sidepod inlet can lead to local thrust being produced

[...]

Very cool to see that bit, because I've had the thought elsewhere. I couldn't really get any input on it, because it seems no one pays much attention to the Ferrari this year.

[siskue2005]

Moreover, don't slotted wings produce less drag than their solid counterparts?

Happy as hell to be educated here.

True, a multi element front wing produces less drag than a single element front wing of the SAME SIZE, with almost same levels of downforce
An aero element with bigger cross sectional area produces more drag (albiet siblge element wing)
so in order to reduce the cross section there are mutli element/slotted wing which in turn produces less drag

[Forza]

Australian GP - Wednesday - 13/3/2013