DaveKillens wrote:Oh yea, a lot of hot air leaves those pipes with respectable velocity. When you factor in the airstream, it most probably accelerates all the air between the lower wing structure and bottom of the wing itself. I doubt if the hot airflow passes over the top of the wing. Each team have their own strategy, some aim the exhaust straight back, like Ferrari.
When BMW took over the Sauber assets, it also included a brand new, state of the art wind tunnel. Personally, I believe BMW have a very good aero package. Sometimes I look at the pictures of the BMW and remark to myself at the clean design. They definitely know what they are doing, and doing it well.
My assumption is the hot exhaust provides a high velocity airstream on the bottom of the rear wing, magnifying the low pressure zone, and downforce.
I wonder if in the future we will see shapes other than the round exhaust, and rectangular exhausts emerge.
It matters not the velocity of the air under the wing, or harkening back to another thread, the diffuser if it increases the pressure upwards from low. If that air/exhaust gas wasn't there to dirty up the flow, then the wing would be most effective. All efforts are made to minimize turbulence heading to the rear wing. That is what McLaren and BMW do with their viking horns and other teams do with airbox "wings". They "condition" the air flowing towards the rear wing. The wing works by having high pressure on top push down while simultaneously having a low pressure zone "suck" it down. Now anything that "fills" that low pressure zone would only be counter-productive by raising the pressure. Still the exhaust must be directed somewhere, and somewhere thats minimally counter-productive.
Sauber BMW does have the best tunnel in the business. It is full size and it permits two cars in tandem to be measured simultaneously. This is unique among all the tunnels used in F1. They can use this to design front wings that have less loss of effectiveness when following in the wake of another car. But one thing that any wind tunnel cannot do is to account for the exhaust gasses (unless they have started running the engines, which I have never heard of yet). And another thing that tunnels cannot measure is the effect that the thermal contribution of the radiators have downstream as they exit warmer air which is more voluminous but less dense. When you hear of teams doing straight line testing, these are among the factors that they are trying to isolate so later on they can have a "correction figure" to fit in the equation with the tunnel data. They set the car up identically as in the tunnel and then, after correcting for barometric pressure (air mass) and humidity (even more air mass) and temperature, they can isolate the exhaust and radiator influences. The first three, barometer, humidity, and temperature are all rudimentary factors with well known equations to correct their influences. How often do we read 1/4 mile times and then see in the fine print "corrected for sea level at X degrees F"?
Which brings us back to the exhaust gasses and how to deal with them. The F2002 was the first car to use the periscope design to get the flow as horizontal as possible. It also had some bodywork shrouds around the pipes that helped scavenge some of the radiator air. The F2004 had some discrete bodywork air exits near the centerling at the base of the airbox. Dealing with radiator hot air is a challenge as well. Renault in 2004 expanded upon the shark gills that the F2003GA used. But now everyone has got the chimneys working so well that gill slits are used only in extreme heat like Sepang. (The chimneys first appeared on the 1999 McLarens mid season, then disappeared mostly until the 2003 Renault.) The gill slits are frowned upon by the aero guys because they mess up the air to the rear wing some. How much more the exhaust? In this case I speculate the the BMW's hot gasses were cooking the rear suspension parts beyond what they could handle with a layer of foil, and that aero had to take a back seat to reliability. Perhaps BMW have gotten the air flowing from the front top of the sidepods flowing downward and hugging the bodywork better than others (which is HIGHLY to be desired) and thus the exhaust wasn't "skipping over" the wishbones as much as other cars.
Anyone with more experience and knowledge is most welcomed to chime in and aid me in my "hack" aerodynamic thoughts. (I dare not call it "analysis".)
Innovation over refinement is the prefered path to performance. -- Get rid of the dopey regs in F1
