2011 Formula One diffuser shenanigans

The FIA likes to try to slow down Formula One cars by reducing available downforce.  They do this for a couple reasons: first, for safety (less downforce means lower cornering speeds; lower cornering speeds mean less-violent crashes when someone gets it wrong); and second, for “better racing” (less downforce means less traction, thus more opportunities for drivers to make mistakes; all this is supposed to produce more passing opportunities).  Rather than simply introduce negative lift criteria in well-defined tests the way they vet each car’s crash structure, though, the FIA tries to reduce downforce by changing the technical regulations.  And when you keep dicking with the regulations, you keep handing the sport’s best designers opportunities to claw back the downforce you thought you got rid of.

In 2009, of course, this was done by cutting holes in the underbody and creating a second diffuser section by shaping the rear crash structure.  These double diffusers were shrilly and vehemently protested by every team that didn’t have one until they managed to add one to their car.  It turns out that a double diffuser is a bit harder to make work than everyone first expected: one reason why BrawnGP did so well while Williams and Toyota failed to impress is that the BGP01’s front wing was superbly designed to play nicely with the car’s diffuser.  It took the teams playing catch-up — particularly McLaren — quite a few race weekends to get their front wings right; once they did, BrawnGP’s advantage essentially disappeared.

For 2010, double diffusers were de rigueur across the field, which means that clever folks like Adrian Newey went looking for other ways to make them more effective.  Newey came up with a rather clever exhaust-blown diffuser, funneling hot exhaust gases through slots in the diffuser roof to speed up flow under the car and thus increase downforce.  This is not a new idea — it was quite common in the turbo era — but making it work properly involved a lot of testing and some delicate ignition mapping to maintain hot exhaust flow off-throttle.  Again, once Red Bull’s advantage was understood it was widely copied, but it took the teams playing catch-up a few weekends to get it right.

And now we’re in 2011, and double diffusers have been banned (we think).  The amount of cutting you can do to the diffuser in general has been heavily restricted, making last year’s blown diffusers obsolete.  So are we now returning to a simpler time where airflow under the car is a small part of the overall aero package?  Not hardly.  Adrian Newey, remember?  Not only has he spent the last year and a half figuring out ways to break the 2011 aero regs, but everyone else knows he’s going to break the regs wide open and has spent the last year and a half figuring out ways to keep up with him.

Which is damn good news for dilettante aero nerds like me.  There’s some cool shit going on in Valencia.

Pride of place goes to Renault.  Rather than try to exploit the starter hole or bend exhaust flow into the diffuser exit via carefully-sculpted gurneys, they simply piped the damn exhaust secondaries out the front of the car to inject flow at the diffuser intake.

That’s just awesome.

One discovers whilst reading about Renault’s solution that long exhaust secondaries — those’re the pipes between the header collectors and the exits — generally favour low-RPM torque, and there’s very little about a modern F1 engine that’s “low-RPM”.  Renault have apparently devised a new engine mapping that compensates for long secondary pipes.

Note that Renault is the engine supplier for Red Bull.


The RB7’s blown diffuser works differently: it injects exhaust directly into the diffuser at its outside edges, which are permitted to have slots cut in them within 5cm of the floor boundary.  This entails long, flattened, faired-in secondaries to get the exhaust where it needs to go; these may block off some flow through the rear suspension (I rather doubt it, considering the attention to detail Red Bull lavishes on its cars’ packaging), but any incidental stagnation it creates would apply even more static pressure atop the floor.  Downforce!

Finally, Ferrari have exploited the starter hole by placing the F150’s exhausts low and close to the car’s centreline.  This directs some of the exhaust flow over the centre section of the diffuser, where it can slip into the starter hole and energize centre-section flow.

I doubt they’re getting as much energy into the diffuser as Renault or Red Bull, but they probably don’t have to worry as much about engine mapping either.

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anarchocapitalist agitprop

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