F1technical.net

strad wrote:why do you assume that is tire smoke?

Because if you watched the coverage you could see that the front right wheel was locked by a failed upright.

marekk wrote:@ ringo:

any comments on this one:



Please note: right tyre's smoke going out of diffuser center.

That is tyre smoke or general dust on the track. I was waiting for this to come up.
The engine is not smoking,so it cannot be engine exhaust.

The car is turning and constantly moving across track. It's likely that the car can move over the path of the front wheel while turning or following the racing line.

For a good representation, look on when the tyre just about failed on the stright. I don't have access to bbc video. You wont see the engine exhaust but you will see how it interacts with the tyre wake.
Try get the shot showing the right side of the car a few seconds after the failure.
The engine is up to speed and the car is still moving quickly.
I think you will see the tyre smoke deflected by the exhaust.

keep in mind as well that this is engine speed dependent, road speed, yaw etc.
Rain may be a good indicator i think.

edit: i can post a snap shot to justify an opinion as well.


why does it go so wide?

and why is there a clean area to the left of the red line, as if there is some force pushing away the smoke?

ringo wrote:

marekk wrote:@ ringo:

any comments on this one:



Please note: right tyre's smoke going out of diffuser center.

That is tyre smoke or general dust on the track. I was waiting for this to come up.
The engine is not smoking,so it cannot be engine exhaust.

Smoke.

The car is turning and constantly moving across track. It's likely that the car can move over the path of the front wheel while turning or following the racing line.

Not true. I've made this snapshot myself. It's in the middle of the long straight.
This one is even in left turn (car going away from smoke source):

I think you will see the tyre smoke deflected by the exhaust.

edit: i can post a snap shot to justify an opinion as well.


why does it go so wide?

Bargeboards + turning vanes in action. Or do you suggest, exhaust is blowing THAT high and wide ? And starts to blow just behind front wheel: ?

and why is there a clean area to the left of the red line, as if there is some force pushing away the smoke?

This force has a name. Imagination.

But the reality looks like this:




And Heidfeld did this lap in +4min - 3 times slower then usual.

In a left turn the back wheel goes towards the smoke.
Also that other picture is clearly sparks and smoke from the floor/plank. Two separate sources of smoke.

I for one was more than a little bit shocked that the Renault team didn't tell Nick to stop on track. He must have wrecked the floor of that car, let alone the front wing.

I know that the BBC commentators made some comments to the effect that "he would want to get back to the pits, get it fixed and get out again" but I wonder how secretive Renault might be about anyone getting a glimpse of the underside of their car if it had to be recovered.

n smikle wrote:In a left turn the back wheel goes towards the smoke.
Also that other picture is clearly sparks and smoke from the floor/plank. Two separate sources of smoke.

Am i talking about rear wheel ?
Never saw smoke from the plank before.

So what are you saying then?

n smikle wrote:So what are you saying then?

I see front right tyre's smoke going to the center of diffuser in left hand turn.

So contrary to what ringo said few posts back, there is no sign of virtual skirts preventing flows on the sides of the car from going under the floor and back to the diffuser..

Otherwise this smoke sourced at front right will have to go outside of right rear tyre on the straight, and even more so in left hand corner.

It may very well be smoke coming from the floor as its clearly sliding on the ground. The smoke coming from front right wheel is going outside of right rear or at least majority of it.

TURU wrote:It may very well be smoke coming from the floor as its clearly sliding on the ground. The smoke coming from front right wheel is going outside of right rear or at least majority of it.

It's just 1 frame, if you look at the whole video, there is some smoke going from the diff almost all the time.

But it could be just burning plank.

We will not know for sure until someone adds few drops of smoke generating additives to renault's fuel

marekk wrote:


Bargeboards + turning vanes in action. Or do you suggest, exhaust is blowing THAT high and wide ? And starts to blow just behind front wheel: ?

barge board and turning vane effect is not that huge.
The exhaust is not blowing that huge, that's mostly tyre smoke, but it is having an influence on it.

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 know some flow will go down there if the pipe is turned fully downsteam and engine speeds are low.



this is a full 180 degree bend and look what's happening. Is this fully effective, or it needs to bend 270 degrees?
Keep in mind renaults pipes are nowhere near the angle and are more sideways than anything.

Maybe some is going there, but not all.
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.

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.

marekk wrote:
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.

How do you think the f duct works?

I just want to see a rain race or a night race.

The f-duct injected air directly into the low pressure side of the wing. The R31's exhausts are not in close proximity to the low pressure zone behind the front wheels. I doubt they have much effect on pressure drag associated with the front wheels.

marekk wrote:
...
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.
...

Of which at least #4 would work better at lower speeds. That might go someway to explain the start of both Renaults and they pace right out of the hairpin in Malaysia.

It just makes too much sense to use the heat as well as the kinetic energy, and the heat can only become really effective under the floor.
Logic would suggest some flow under the floor and some flow pushed to the sides.

I still have to be convinced of it being either way.