03-17-2011, 06:08 PM
There’s some cool science here …
Fun fact: An NHRA dragster develops 600lbs of downforce from it’s upturned exhausts at full throttle.
This new Renault has them pointing DOWN. The Aero Boffins must really like their numbers to pull this stunt.
Let’s look at them …
An F1 exhaust cannot be worth 600lbs. Dragsters run on nitromethane which has 8 times the explosive capacity of gasoline. F1 exhaust must be a number closer to 60lbs then.
Renault is then proposing – dependent on throttle position – there will be from zero to sixty pounds of uplift ahead of the car’s centers of gravity and aero pressure. The further ahead of center, the greater leverage the exhaust flow has on car balance.
Let’s imagine such an effect along with Kubica and Petrov through the not-quite-flat Maggots/Becketts Complex … in car’s which, at the limit, need only the force equivalent of a single finger to tip them into a spin … the contra-flow with the airstream making it a whole different kettle of fish from the variable downforce problem presented by rear facing exhausts …
Unless, they really do point FORWARDS. This solves the contra-flow problem.
Nor, as you might at first think, is it a problem to have outlets facing into the incoming airflow. The flow differential is no contest in favor of the outgoing hot exhaust gases at 800 liters/sec. (Math: 300 revs/sec x 2.64 liters = 792 l/sec.) Blowtorch in a breeze … even at 320kph.
The drag penalty is almost zero because the forward facing pipe is always pressurized, blocking incoming flow (as in: trying to fill an already full cup – the incoming flow is blocked.)
You still have to account for the hot exhaust gases being channeled underneath the sidepods. Thermal convection and radiator inflow draft would seem to naturally pull the stream upwards.
Unless, the flow energizes not the underside flow, but the sidepod undercut flow. Acting outwards, not down. This would make it primarily a drag reduction trick, not a downforce production trick.
In which case: Yeah baby, please cut my drag at full throttle!
Conundrums like these is why the Aero Boffins use the fastest computers in captivity to back up what otherwise would be wild-ass guesses. (Behold the proto-singularity!
We’ll find out as testing unfolds.
… and there’s your cool science.
To try at home: (Worth the bother
If you care to feel a “variable downforce effect” with you own fingertips, do the following experiment. No super-computer required.
Go to your kitchen.
Take an ordinary teaspoon (you know, one conveniently shaped like an upturned wing when viewed in profile
At the sink, run the tap.
Holding the handle between thumb and forefinger, slowly move the spoon bottom toward the waterflow.
When the bottom hits the flow, you’ll feel the spoon be sucked in.
Magically, you’ll have downforce at your fingertips. If you bob the the spoon bottom in the flow you’ll feel the “downforce” vary. If you just let it hang, pulled in by the flow interaction alone, you’ll feel a fluid finding it’s own equilibrium.
Extra credit: Take a moment to feel the lift-to-drag ratio of your teaspoon. It’s the difference between the pull-down of the waterflow and the pull-in to the waterflow on the spoon. If you feel compelled to try every spoon in the house, looking for the best lift-to-drag ratio, you have a taste of what motivates an aero boffin.
Taken from a blog post not my thoughts this stuff is above my head.
~2013 Porsche 911 Carrera
~2013 Mini Cooper GP SOLD
~2013 Porsche Boxster S SOLD
~2011 E90 M3 AW SOLD