ringo wrote:
Tell me though, why do you want the flow to go under the diffuser?
It's effect will be minimal compared to the other solutions that have the pipes right by the diffuser where it can get maximum energy.
I am willing to accept any logical explanation, but there isn't much facts to support the diffuser being blown.
It could well be, but there is no evidence for it.
I find that blowing wide has multiple benefits that positvely improve the diffuser as opposed to desperately blow the diffuser, and not even do it effectively.
We have to wait for the finel evidence, where is this exhaust realy going - our speculations are just this... speculations.
But we can talk about facts.
1. Total energy of exhaust gases is around 500-600kW.
2. For a total mass flow of 0,45kg/s, even at 200m/s (which is way to high in my view), kinetic energy of flow is 9kW, less then 2% of total energy. At 100m/s it's just 2,25kW
3. The rest is heat.
As you can see in your simulation, exhaust gases quickly cool down, by mixing with external flow, heat transfer to the tarmac and floor, radiation.
If exhaust goes under the floor and to the diffuser, one can have following gains:
1. Kinetic energy (exhaust has momentum more or less perpendicular to longitudal axis) is used to "widen" flow lines from leading edge to diffuser. This means more area covered, longer paths/more time to accelerate flow and more downforce.
2. Heat exchange/mixing with external flow means higher gas temp under te floor. Hot gases have less density and inertia, so they accelerate better then cold ones, achiving higher speeds - this is less static pressure and more downforce.
3. Hot gases under the floor and in diffuser decrease boudary layers thickness and prevent flow separation (especially in highly loaded diffuser).
4. Mixed flow cools down partially due to heat transfer and radiation - gases contract as they cool down. Created void is low pressure, so more downforce. As the gases around rush to fill this void, they accelerate - more downforce.
How much of the energy of exhaust one can realy use to do this work, depends on many factors, current speed of the car (external flow) being most important one. Slower car means more time for exhaust under the floor to cool down, so better efficiency.
I'm quite sure not all of exhaust goes under the car - it's almost impossible to have such control over the flows, and they can deliberate try to direct some part of it to the rear tyres, where less dense and more turbulent air will be of real advantage. This vertical wall inside the pipe could be used for this - flow speed around a curved pipe is not uniform, if you place this separator at right place, you can have 2 flows with different speeds.
I don't think one can significantly decrease drag by blowing all exhaust gases into low pressure wake behind front tyres - volume/mass flow of exhaust is simply to small compared to amount of air displaced by the tire, and at high speeds of the car, when drag reduction will give biggest gains, even more so.
Hopefully one day they fill to much oil in the tank and we will see.
