Open ended questions about exhausts and downforce

[olefud]

Only well after it departs the car’s surface will the exhaust equalize with the atmosphere with the mentioned heating of the atmosphere as a system.
Of course, sans overrun fuel input and with extraction of energy by electrical compounding, the heating will not be of a magnitude as in days past.

currently engines have on the overrun continuously managed power settings to minimalise backdrive torque/aka engine braking (in conjuction with recovery action)
this effect will be increased in 2014
also, on the overrun, compounding would be suspended to retain turbo rpm as much as possible ?

so there would be quite a lot of exhaust heat around ?

I was thinking of past dumping in fuel with the ignition shut down. Your point about reverse compounding on overrun is well taken.

[shelly]

For me the advantage comes not only from momentum, but especially from vortex intearction = adding momentum to a vortex along its axis. The stream tube gets narrower but depression increases because of conservation of ANGULAR momentum. An accelerated vortex is much more effective for downforce generation.

[hollus]

Wouldn't the vortexes that can interact with the exhaust be on top of the floor of some other surface? They would then generate lift. I can see the exhaust momentum used to direct vortexes for the purpose of redirecting air, but not to use the internal lower pressure directly. Where are you proposing these vortexes go to?

[shelly]

It is not a redirection in my opinion, but an acceleration. The exhausts accelerate the vortex that rolls around the outer edge of the diffuser and goes under it- so the low pressure generated downforce on the footplate and on the diffuser (surfaces facing down).

[godlameroso]

For me the advantage comes not only from momentum, but especially from vortex intearction = adding momentum to a vortex along its axis. The stream tube gets narrower but depression increases because of conservation of ANGULAR momentum. An accelerated vortex is much more effective for downforce generation.

Similar to how hurricanes use convection from evaporating sea water to feed themselves into stronger and more organized systems. I had a theory that exhaust blowing was taking advantage of this, albeit instead of using hot evaporating moisture laden air in large volumes, we're using a localized extremely hot but comparatively low volume to power the vortex generated by the bodywork.

Again not as the primary goal but merely another advantage of using exhaust blowing.

[godlameroso]

Wouldn't the vortexes that can interact with the exhaust be on top of the floor of some other surface? They would then generate lift. I can see the exhaust momentum used to direct vortexes for the purpose of redirecting air, but not to use the internal lower pressure directly. Where are you proposing these vortexes go to?

They could be used to feed the underside of the brake duct winglets. Also remember you can use vortices to isolate flow going to surfaces adjacent to said vortex. This would benefit the beam wing and top side of the diffuser.

[shelly]

For me the advantage comes not only from momentum, but especially from vortex intearction = adding momentum to a vortex along its axis. The stream tube gets narrower but depression increases because of conservation of ANGULAR momentum. An accelerated vortex is much more effective for downforce generation.

Similar to how hurricanes use convection from evaporating sea water to feed themselves into stronger and more organized systems. I had a theory that exhaust blowing was taking advantage of this, albeit instead of using hot evaporating moisture laden air in large volumes, we're using a localized extremely hot but comparatively low volume to power the vortex generated by the bodywork.

Again not as the primary goal but merely another advantage of using exhaust blowing.

i just partly agree with you. In my view the thermal effect of exhaust is negligible and vortex stretching is essentialy given by speed-momentum; and I think that this is the main effect, the primary goal

[rjsa]

So you are suggesting that the hot air flow leaves the exhaust system, cross the gap on the fairing, to merge with external free flow and then enter the diffuser from the top while still keeping a speed relative to the same diffuser that is fast enough to make a difference?

[shelly]

Exahusts - in my opinion - enter from the side more than on the top of the diffuser -along the footplate edge. Yes I think there is enough momentum to make the difference, especailly at low to medium speed of the car

[rjsa]

Y u are aware that by regulation the exhaust piping points upawards and whatever exhaust flow gets to the diffuser is what was diverted by the free flow around the sidepods, right?

[shelly]

It is a fact that exhausts reach the diffuser. Then every analysis stops, and everybody hides behind phrases such as "to better seal the diffuser" - "in order to run an higher rake". I would like, like godlameroso I think, for the discussion to start from here and talk about the benefits of having exhausts there - the describe which are the phenomena that meake this universally acknowleged "seal" happen.
What is your opinion?

[wesley123]

The "power" of the exhaust simply prevents airflow from the wheels spill into the diffuser area. This effect is mostly described as a 'wall' because it sits in between 2 different zones.

Because of this 'wall' that is created teams can create more efficient diffusers and run more rake.

[shelly]

Agree with that wesly. But what is the physical cause of this wall?
For me it is momentum - the momentum the exhaust add in longitudinal direction.
But since there is a coherent vortex in that zone with a longitudinal axis - the footplate vortex - the injection of longitudinal momentum srteches it, and this is the bigger downforce effect in my opinion

[rjsa]

The exhaust flow is channeled into the diffuser which has an opening clearly visible in the first picture to capture air that comes from above the floor. Within the vertical walls.

My intuition (since there's no way I can run tests on such a setup or have the math to prove anything) says that it's the addition of hotter air to the flow being pulled from the floor ahead of the diffuser that will accelerate the flow along the venturi exit ramp - crating lower pressures at the venturi choke point, under the floor right ahead of the diffuser.

[shelly]

I think the exhausts do not go into the starter motro hole as you say, they should go between footplate and wheel instead.
The enter the diffuser spiralling in from the side / footstep