BMW exhausts

[Shaddock]

Hi guys, this is my first post and I was just reading some old post when
I came across this thread. Here's my theory on what they could be trying to achieve.

BMW have been fairly radical this years in terms of aero and maybe this is part of there blue sky thinking. My theory: Hot gases blow onto the rear wing, heating the elements, this increases the wings elasticity allowing the wing to operate in two aero distinct states.

Would this work in practice? not sure Would a team try it ? possibly.

[Tom]

Welcome to THE forum Shaddock,

I like this idea alot, I can't remember if air pressure changes in heat but I think it does (ready to be corrected) and seeing as the hottest gases would most likely be released when the engine is working hardest down the straights, when downforce is nedded less, I suppose there could be some real gains to be made.

Remember we still don't know much about aerodynamics, it was only 20 years ago that Chapman was introducing ground effects etc.

[DaveKillens]

Hi Shaddock, welcome to THE forum. I have always believed that teams use heat to circumvent the testing procedures. They test deflection while in the garage or parc ferme, and it's my belief things such as engine and exhaust heat are directed to change the properties of things like the wings. Not that the conditions change from corner to corner, but the general heating allows parts of the wings and attachment points to allow more flexing than the rules allow.
I don't think it's a good idea to allow the exhaust to reduce the wing downforce due to RPM, that could lead to lots of problems on long, fast sweeping corners

[Shaddock]

If you discard the heating factor, at a certain loads (high speed) BMW's slot gap on the rear wing was increasing earlier in the season reducing its drag.
This may just be another way to get passed the FIA static tests for flex/rigidity of aero devices although I would imagine it would be nightmare to manufacture.

[scarbs]

Judging by the weathering on the bodywork from the exhaust, the exhaust flow soon curves back down around the tail lamp, notice the shape of the black heatsheild. So I doubt its heat directly plays on the underside of the front wing.

BTW there is a patent on a heating system for the skin of aircraft wings, this reduces the viscosity and hence thickness of the boundary layer, allowing steeper geometries to be tried without drag\stall issues.
A hotter racecar wing might also benefot from this effect, whether it be indirect heat or a heater laid into the wing itself.
I asked McLaren and Lola aerodynamicists about this they thought the effect would be negligible.

But then they woudl say that wouldn't they.

[AeroGT3]

Dcdugas, then please explain why an eductor can work the way it does? It's because the high velocity fluid coming from the central nozzle entrains the fluid surrounding it, and draw it along. This is the concept I am trying to sell.
http://www.1877eductors.com/tank.htm
Just replace the central nozzle with the exhaust pipes, and the secondary, larger bellmouth with the diffuser, or wing structure.

The exhaust isn't going that much faster than the normal wind because it isn't that focused by the time it nears the wing. Moreover it is still pointing up! It would have to go signifigantly faster than the air stream and it would have to be largely horizontal. The 500 km/h figure is highly dubious, but even if it were near that it, if it spreads from 80mm to just 160mm by the rear wing, then it would be going only 125 km/h (slower than the airstream), and it would be filling the low pressure zone under the wing element, thus negating it somewhat.

In your link they are talking about liquids which are different than gasses because gasses are compressable and liquids aren't to any appreciable degree. The effect described in that link is related to the ventury effect. However if it were possible for a focussed stream to be passing through a low pressure zone with a signifigant delta in velocity, then it could "punch through" the low pressure zone and drag surrounding air with it thus lowering the pressure even more but we are talking huge deltas (3X-4X minimum) in velocity and a very focussed stream in order to achieve the effect otherwise the low pressure zone will destroy the focus of the faster stream and increase in pressure. It has to be faster by enough to "punch through" the low pressure zone and it has to maintain its focus.

There are two principles you are totally failing to grasp. You CAN add air mass to a system and decrease pressure, so long as the mass flow out of that system adjusts to account for that influx.

And INDUCTION pump works just like the exhaust pipes would. I actually have real, tangible lab data from an induction experiment I did last year. Let me know if you want to see it. Basically, when you turn on the engine, you spew VERY fast moving exhaust gas, at VERY low pressure into a flow. The exhaust gas, or jet flow, is low enough in pressure to lower the pressure of adjacent air, and the shear layer between the slow and fast air speeds up the slow flow. It works and I can prove it with an experiment I did.

The other thing is circulation control. You may think the exhaust "dirties" the air, but it may very well clean it up. The exhaust gas flowing out has become a streamline of the flow, and the flow field around it will now change in a way that may very well help the rear wing. Google "circulation control wing" or circulation control. It is a hot aerodynamic topic and it's been introduced on things from planes, to submarines, to semi trucks.

As to whoever mentioned continuity and momentum, thanks for showing that there are people on this board with a legitimate understanding of the fundamentals!