Saturday, March 17, 2012

Mercedes' DRS-activated F-duct

Despite the prohibition on driver-activated aerodynamics other than the DRS, Mercedes have themselves a DRS-activated F-duct ('fluidic switch'). It seems that if a fluidic switch is activated by driver-activated DRS, then that fluidic switch does not constitute driver-activated aerodynamics. Curious.

Speculation continues, however, about the exact purpose of Mercedes' F-duct. There are slots in the undersurface of the front-wing, and Craig Scarborough suggests that the purpose of the system is to blow the front-wing.

Here's another possibility, however. One of the advantages of the active-ride Williams FW14B was that it reduced drag in a straight-line. Here's how:

"We realised in the wind-tunnel that if we lowered the rear and raised the front, you could stall the diffuser and that reduced the drag of the car significantly...I can't remember the figure but that would give them something like an extra 10 kph," (Adrian Newey, p233-234 in Williams, Maurice Hamilton, 2009).

So could Mercedes be stalling the diffuser somehow? The diffuser downforce depends upon the vortices which peel off its lateral edges, hence if one could blow these edges, one might be able to stall the diffuser.

3 comments:

lightsun said...

Hello,

First of all I want to tell you that your blog is awesome. Congratulations for it.

Just wanted to comment that the idea of stalling the diffuser is currently used in fast tracks like Monza even without the use of any kind of duct (at least they told me that in a job interview as Aerodynamicist in a F1 team a few weeks ago).
From my point of view, stalling the diffuser gives a better drag reduction, and it is easier to put a small vertical duct instead of a very complicated duct from the rear to the front of the car, although the aerobalance would be critically shifted forward.

Gordon McCabe said...

Cheers muchly!

That's a fascinating insight. Do you know exactly how they stall the diffuser at places like Monza?

lightsun said...

It was simply playing with ride heights. I think that lowering the rear ride height is enough to reduce the amount of air going through the diffuser and stalling it.

Taking a look at Cooper papers about diffusers with a simplified squared model(SAE Ref 2000-01-0354), the lift coefficient falls quite fast if you reduce the Area diffuser outlet/area diffuser inlet. So in a F1 car, I think that lowering the Rear ride height it should be quite easy to make the lateral channels of the diffuser stall.