Exhaust Blown Floor - Forward Exhaust Exit

[hardingfv32]

What would be the advantage of the exhaust flow entering the under the side-pod floor (not the diffuser)?

I was under the impression we would have skirt to the ground, if allowed by the rules, to seal the sides of the side-pod floor.

Brian

[PlatinumZealot]

Yes, one argument is the skirt. Another argument is that it blows the diffuser but more evidence points towards the creation of a delta shaped skirt from the leading edge of the floor backwards.

[marekk]

Obviously, where the exhaust gases in the end go, depends on many things, car's actual speed and tip's shape and angle being 2 most important IMO.

When you compare exhaust angle in Turkey (high speed corners) and in Canada (stop and go), they vary very significantly.

It's not like all goes sideways or all goes to the difuser, always.

It's multifunction device, sort of. Maybe this time tuned mostly to help with traction and braking by blowing out excessive water in front of rear tyres in slower parts of the track ?.
That said, i've found (after carefully looking at the available coverage of Montreal 2011) no evidence of exhaust going sideways at higher speeds.

@ringo - flows don't bend at 90 degree. Nothing with mass can change direction instantly. No need to repeat this month after month.

[ringo]

I have to as the same thing keeps popping up.

There is evidence of it going sideways at higher speeds. Many times we see the car puffing aside water through the turns. And the turns are where it is most crucial.

[PlatinumZealot]

Interesting comments from James Allison. I think this was put forward by the "skirt" supporters. Just some more evidence that a skirt is made and the DF is more forward biased.

http://www.autosport.com/news/report.php/id/92500

Although there are suggestions that the changes are aimed particularly at slowing Red Bull Racing down, Allison said on Tuesday that it will affect all teams.

"The FIA's note will cause all teams, whether or not they use a blown floor, to change their operation," said Allison.

"The headline changes for the Silverstone GP are as follows: when the driver lifts his foot fully off the throttle pedal, then the ECU maps must be set up so that the engine [to all intents and purposes] closes the throttle - previously it was possible to configure the engine maps to leave the throttle open and reduce the engine power by other means.

"Furthermore, when the driver lifts fully off the throttle, the ECU maps must be configured to cut off the fuel supply to the engine – this is intended to prevent so called 'hot blowing' where the energy of the exhaust gas is increased by combustion."

Allison, whose team pioneered the radical forward-exit exhausts this year, conceded it was difficult to know how the changes will affect the performance of its car.

"It is not easy to judge the effect of this change on our competitiveness. The loss for each blown floor car will come from two separate effects – how much downforce will you lose and, in addition, how much will the loss of this downforce upset the balance of the car.

"All blown floor cars will lose downforce under braking as a result of these new restrictions. Some teams will lose more and some teams less; it is hard to know exactly what relative loss LRGP will suffer.

"However, it is possible that we will suffer less on the balance shift side of the equation because our forward exit exhausts produce their effect quite near the middle of the car. This means that as the exhaust blow waxes and wanes, it does not really disturb the aero balance of the car too much.

"With a rearward blower, the downforce from the exhaust is all generated at the rear axle. As the new rules reduce the blowing effect on corner entry much more than corner exit, it is possible that the rearward blowers will tend to suffer more nervousness under braking and more understeer on exit as a result of the new restrictions. We will find out in Silverstone."

He also made it clear his team is against changing the rules during the season.

"We would have preferred the status quo to remain for the rest of the season," Allison added.

[hardingfv32]

"more understeer on exit as a result of the new restrictions."

Why?

Brian

[malcolm]

"more understeer on exit as a result of the new restrictions."

Why?

Brian

Presumably because the car would have to be set up with more rear grip to offset the lack of downforce on corner entry, compared to the current off-throttle blown-diffuser. Of course, when on-throttle, the car would generate more rear downforce and naturally make it want to understeer. You could minimize that with shock settings, but you'd be fighting against a distinct difference in aero balance.

But, personally, I think teams would have the ability to set up the car and incorporate a few minor updates so the ban has a minimal effect.

I doubt there will be much of a difference in the running order... I expect Red Bull to remain the quickest.

[Bob_tm]

Who can stop drivers to push both pedals under braking? First 10% of maps - more fuel, less ignition, more air with intake cam and early opened exhaust cam. A lot of exhaust and no power. Just throttle under braking instead of blue or red buttons And yes, "when the driver lifts fully off the throttle, the ECU maps must be configured to cut off the fuel supply" should work, but never used


Blown diffuser should speed up air under the car. So why some teams lose only rear downforce? I'm thinking the should loose front and rear downforce.

[ringo]

where is shelly?
[youtube]http://www.youtube.com/watch?v=5TXbL-JTTMM[/youtube]
Shelly?
Why is the amateur CFD so accurate?

Why the prediction that the downforce is produced in the middle. Was it all a lucky guess on my part?

switch sides Shelly.

Come on Shelly,

Come on!!!

[shelly]

ringo, if you had read my posts you would know that I have always said that one of the main advantages of fee is front suction peak increase.

So you have no reason to behave like this now; I advise you to read the posts instead.

[ringo]

Heh i was just kidding shelly.
That name always reminded me of this old skit. I just needed an excuse to post it.

It couldn't apply to you precisely, as i would be the fat guy in the suit persuading everyone to dump the blown diffuser theory.


Slowly but surely we are learning and confirming the details of this exhuast setup.
As silverstone comes along we will see which technique suffers most.

I would say the rear diffuser blowing will suffer the most as it works on a slightly different principle.

When i get the time, i will find the exhuast temperature with low fuel injection and 10% throttle and compare both front and rear hot blowing.

[ringo]

@ringo: it is not haer say against evidence. But if you do not want to discuss because you can not put on the table something more solid than "it's in the images", then ok.

You have not recognized a F1 areodynamicist (SLC) even when he posted on this forum, so probably even if you get to chat with another one, you will question their opinion if it forces you to rethink your approach.

@expensive: biggest role in deflection is played by the flow on the side of the car, travelling at a little higher sped than he car's.
Then there is low pressure under the floor, and even lower pressure in the kink line region.

Shelly i was responding to this, not your other posts.
It is a wrong assumption.

Everything shouldn't be falling into place if i was reading pretty images like Rorschach cards.

I must also tell you that sucking air under the car is not the right thing to do anywhere behind the diffuser throat.

The diffuser is an open system. There is conservation of mass flow.

mass flow in ---> mass flow accumalation ----> mass flow out.

Under an F1 floor you don't want any accumulation under the floor. Everything that goes in needs to come out. And the exhuast is actualy to promote the revers of accumulation.
It is actually trying to increase out flow rate over the in flow rate. This means the sytstem may no longer be steady state and the sytem boundary moves.

There is a lot to it, but it doesn't make sense i throw it all out, just for it to be hit back from some hear say.

[shelly]

I think that exhaust gases follow aa bow trayectory, and enter the floor by the sides before the kink line, increasing downforce. This effect aadds to increased front suction peak.
Do gases go 100% under the floor? Do they partially/totally go outwards, on rear wheels or wider?
As I wrote before, wa can not conclude on exhaust trajectory using PC CFD (or worse EFD).
ringo, you must not mix the two things up: the effect on front suction peak is obvious/evident, the rearward trajectory is difficult to predict.

There is nothing "falling into place". What do you think is a wrong assumption on my side? And what do you think is hearsay?

About sucking air form the sides:
- if you suck it in before the kink line, you will get more mass flow rate, an increased suction peak on the line, thus increased downforce
-if you suck it in in the diffuser from the footplate, you can get some downforce from the vortex on the footplate edge

Yes there is a lot to it

[ringo]

No you don't want air entering the sides of the floor.

There is a misconception that fans have, when they hear "feed" air under diffuser and "feed" the floor.

The teams are forcing air under the floor, you really want less air as possible.

What you don't want is the air to enter faster than it leaves the floor.

If that happens then it becomes a case of accumulation, and then stagnation.

When air is fed under the car, it is really just to prevent stagnation and circulation from occuring.

You don't put air under the car increase downforce, as ideally the opposite is better.

To get an idea of what i mean, let's say air enters the floor at 2 kg/s.

And then it leaves at 1 kg/s.

What is happening is that 1kg of air is staying in the sytem every second. It will reach a point in time where the floor effectively chokes, or certain parts of the floor is chocked and the floor behaves like a restriction.

So i never prescribed to the idea of injecting air under the floor. It never creates downforce.
You only inject when it is required, and you only inject ahead of the diffuser throat, no where else.

[ringo]

I think that exhaust gases follow aa bow trayectory, and enter the floor by the sides before the kink line, increasing downforce. This effect aadds to increased front suction peak.
Do gases go 100% under the floor? Do they partially/totally go outwards, on rear wheels or wider?
As I wrote before, wa can not conclude on exhaust trajectory using PC CFD (or worse EFD).
ringo, you must not mix the two things up: the effect on front suction peak is obvious/evident, the rearward trajectory is difficult to predict.

There is nothing "falling into place". What do you think is a wrong assumption on my side? And what do you think is hearsay?

About sucking air form the sides:
- if you suck it in before the kink line, you will get more mass flow rate, an increased suction peak on the line, thus increased downforce
-if you suck it in in the diffuser from the footplate, you can get some downforce from the vortex on the footplate edge

Yes there is a lot to it

The car does not "suck" air from the sides. Look on any picture of an F1 car in the rain.
This is not a tunnel floor. It is a flat floor. Old time rules of thumb cannot apply to these cars today.

The air actually diverges from the splitter backwards. The body of the car pumps the air to the sides, so there is no migration inwards to the diffuser.
Nothing from the outside will cross the flow lines and get sucked into the diffuser.