Exhaust Blown Floor - Forward Exhaust Exit

[Richard]

Richard you said the exhaust kicks up the dust(and as seen in the video), So can we all agree that the initial velocity of the gas is outwards and away from the car?

Yes, at the point of impact. The dust probably doesn't tell us if it is the bottom of an anticlockwise vortex (viewed from the front) flicking the dust up and outward (like a cyclone vacuum cleaner) , or a simple outward jet.

[shelly]

Richard you said the exhaust kicks up the dust(and as seen in the video), So can we all agree that the initial velocity of the gas is outwards and away from the car?

Yep

[malcolm]

1) My stance isn't that the diffuser is some mega-powerful super-vacuum that sucks marshals' hats off their heads as the car drives by.

2) People are saying that dust will follow the air/exhaust stream precisely. I disagree, as it's impossible since the air/exhaust is what is propelling said dust.

3) Even looking at those photos, ignoring the potential effects of turning, inertia of dust particles, drag forces experienced by dust particles, etc, the inner part of the exhaust stream may still end up going under the diffuser (maybe 5%...?). Sure, the majority may shoot wide of the car, but since the exhaust stream widens as it mixes with the cross-flowing air, it's not some far-fetched miracle that some exhaust could end up being drawn under the diffuser.

Also, Ringo, your jokes aren't very obvious (to me, at least), and more often than not, it seems more like an insulting sarcastic comment than a joke. Just my two cents.

[marekk]

OK.. so, this is a two part problem...

1) Proving that the exhaust gasses can turn such a tight radius - From pipe exit at 600mph at a trajectory of say 30 degrees, then in about 1 meter distance it turns back under the car..
(It has to turn because there is irrefutable proof that it is shot out sideways from the car)... Sounds crazy already.. but it can be worked out.

Still didn't got why that sounds so crazy to you.
Apart from details (don't think exhaust gases reach that far, and 600mph is a little on the high side for me) we have basicaly just two oposite forces in the game: exhaust gases momentum directed outwards, which, if we believe in ringo's numbers, will be around 40 kgm/s per side, 80 kgm/s total, and floor/diff sucktion, acting along the sides, worth at least few hundred kg.

And think about timing: at 50 m/s car speed and 10 cm pipe diameter, you blow for only 0,0002s into given point of external atmosphere , but you are sucking from it all along the floor for 0,04s. Plenty of time for atmosphere molecules rushing to fill the low pressure area under the floor to deccelerate very light (in comparision to cement dust or water droplets) exhaust particles and accelerate them back.

Could be totally wrong as well, but can't see anything crazy from the basic physics point of view.

[PlatinumZealot]

Ok, honestly I think the theory of the gasses curling under is not realistic, but I am open minded and I created this diagram for you and the supporters of the diffuser sucking in the air. You figures, i am not sure what they are based on, but put it on this diagram.. maybe a momentum diagram if you want.
I am working the maths and I will try to fill it out.. I will see I can come up with a net force needed to bend the gas, which is going 315 m/s, within a radius of about 3 meters...



Keeping in mind these pictures..

[ringo]

I think the bullet example is good even if we do not take into account reversed flow. It shows that the gases do not reach as far as the bulet. It is the same as the feather- ball example I posted.

I think you can not disagree that heavy and light particles have different trajectories in a flow field.

It's not even close. Not a good example.

Would you consider a bullet and the gases a homogenous mixture?

Let us break the argument.
Do dust go under the diffuser? No
Do exhausts and dust follow the same trajectory? No (maybe only ringo has not got it yet)
Where do exhausts go? We can discuss it, but dust gives very little answer to this question
I have understood the push-pull issue, which is blown away (pun!) if we consider negative relative pressure (so the vaccum cleaner example fits)

Draw it please. Which trajectory does it take. Trajectory is different than magnitude of trajectory. The dust follows the gas, which in fact goes further than the dust because of the magnitude of the velocity.

I think the bullet example is good even if we do not take into account reversed flow. It shows that the gases do not reach as far as the bulet. It is the same as the feather- ball example I posted.

I think you can not disagree that heavy and light particles have different trajectories in a flow field.

So the gases go further out than the cement dust then?
It's hurting the diffuser theory even more. I'm well comfortable with the conclusion, but i am curious as to how you guys visualize your own opinions.
Put in a little energy to make a diagram. I want to see what you think.

[ringo]

1) My stance isn't that the diffuser is some mega-powerful super-vacuum that sucks marshals' hats off their heads as the car drives by.

2) People are saying that dust will follow the air/exhaust stream precisely. I disagree, as it's impossible since the air/exhaust is what is propelling said dust.

3) Even looking at those photos, ignoring the potential effects of turning, inertia of dust particles, drag forces experienced by dust particles, etc, the inner part of the exhaust stream may still end up going under the diffuser (maybe 5%...?). Sure, the majority may shoot wide of the car, but since the exhaust stream widens as it mixes with the cross-flowing air, it's not some far-fetched miracle that some exhaust could end up being drawn under the diffuser.

Also, Ringo, your jokes aren't very obvious (to me, at least), and more often than not, it seems more like an insulting sarcastic comment than a joke. Just my two cents.

What is the goal in that case. Tell me.
It's an extremely poor design if this , in bold, is the ultimate form of creating downforce.
Trust me, if only 5% of the gas goes down there, then it's a failed blown diffuser as you should know. You need maximum speed and temperature in contact with the parts of the floor. Curling back, which doesn't happen, cannot give this.

Focus on the observation than trying to fix it so that the gas goes into the diffuser.
We need to be as unbiased as possible and look on what is happening in the shots.

Shown is the car going in a straight line after the turn.

The dust is still being blown very wide of the tyre, and it does not fall to the ground.
It is being carried by the exhaust gas.

Agree? Please respond directly because shelly is dodging all the questions i am asking, while i am responding to all his/her's posts.

[ringo]

My first thought on seeing the video is that the car is turning, the exhaust is kicking up the dust, and we are looking at a trace of the car's path around that bend.

We can't discount that the car is turning. The exhaust kicks up some dust, the car travels forward and turns right, so the point at which the dust is kicked up is then offset to the side of the car.

There is also some merit in the water splash analogy. The initial impact of the exhaust would be outward. However, would the dust continue on that path if the exhaust formed a vortex down the edge of the car? Is it reasonable to expect the dust to form a nice vortex like smoke in a wind tunnel, or would the dust kick up and get flung out as the vortex hit the ground?

Finally, how long had the dust lain there? Had it previously been stored in a bucket, open to the damp sea air?

Richard here is a straight:

This a snap shot from the car moving straight for quite a while.

[malcolm]

Haha, ringo, I said about 30 pages ago that I don't think it is the primary design criterion. All along, I have only taken exception to the suggestion that ALL exhaust gets blown wide. I still think that some gets in there, and may provide a small benefit.

Your CFD, while the jury may be out on the accuracy, certainly shows that the forward exhaust may create a diffuser of sorts that increases front downforce.

So what do I think? Probably an attempt at an elegant solution to increase downforce by creating a diffuser effect behind the leading edge of the splitter and front of the floor, lowering drag by filling in the wake of the front wheel, and a bit of that exhaust either ends up going through the diffuser, or it heats up some of the air that goes under it.

The photos of the dust don't really show much to me, other than where the outside of the exhaust stream is, roughly. Obviously, the outside of the dust cloud obscures the part of the cloud nearest to the car, so we can't really see if some of that dust is getting pulled inward or not. Not the greatest of visualizations, since the unimportant part obscures the important part.

[shelly]

I think the bullet example is good even if we do not take into account reversed flow. It shows that the gases do not reach as far as the bulet. It is the same as the feather- ball example I posted.

I think you can not disagree that heavy and light particles have different trajectories in a flow field.

So the gases go further out than the cement dust then?

ringo, do you read others' post or do you just reread yours? Dust is blown outward, while gases are inward. I have written it several times and all the others here agree on that.

The fact that gas and dust mix does not imply they have to stick together forever.

That pretty much closes the dust issue, leaving open the discussion on trajectory. What do you mean by "magnitude of trajectory"?

The probelem seems that you have not realized that whta you put forward as proof of your points on trajectory lend themseles to strong objections for which you have not given answer (maybe because is not there).

You call for dust and rain patterns as proof, but they are too heavy so they are not; you call for opticla distortions due to density, but they can not be visible under the shadow of the floor; you post cfd picture, but this level of detail is beyond what can be realised with homemade cfd.

So you can not rely on these things as evidence to prove your point; you should try something differnt, like smikle is doing. For exampleasking for evidence abot where does th outward momentum of the exhausts go, and expecting it to go outward if there s not some force to nullfy it and invert it. And so on.

[marekk]

Ok, honestly I think the theory of the gasses curling under is not realistic, but I am open minded and I created this diagram for you and the supporters of the diffuser sucking in the air. You figures, i am not sure what they are based on, but put it on this diagram.. maybe a momentum diagram if you want.
I am working the maths and I will try to fill it out.. I will see I can come up with a net force needed to bend the gas, which is going 315 m/s, within a radius of about 3 meters...

Don't think you should add speed of exhaust to the speed of the car. Along the axis of the car they subtract, perpendicular to the axis it doesn't change (at least at the straights).

[ringo]

He's looking at the ground speed.

So what do I think? Probably an attempt at an elegant solution to increase downforce by creating a diffuser effect behind the leading edge of the splitter and front of the floor, lowering drag by filling in the wake of the front wheel, and a bit of that exhaust either ends up going through the diffuser, or it heats up some of the air that goes under it.

That is the whole deal.
This was expounded on months ago. And it makes a lot of sense.

ringo, do you read others' post or do you just reread yours? Dust is blown outward, while gases are inward. I have written it several times and all the others here agree on that.

This is not possible IMO. I've asked you to sketch how it is possible and you have not responded. Ever used a leaf blower to blow dust?
It would be a useless tool if the dust went the opposite of the blowing direction.

Secondly it would be breaking Newton's laws if the exhuast gas go out 1 or 2m then curl in back 2m without any external forces being applied to them.
So i'm not gonna try to pick your brain for that one, unless you draw a diagram demonstrating it.

The fact that gas and dust mix does not imply they have to stick together forever.

That pretty much closes the dust issue, leaving open the discussion on trajectory. What do you mean by "magnitude of trajectory"?

2 things can move along the same exact line and not have the same displacement or speed. Differing magnitudes.
the particles move with the same direction, they only don't go as far as the gases.
The gases do go further outward than the cement particles.

The probelem seems that you have not realized that whta you put forward as proof of your points on trajectory lend themseles to strong objections for which you have not given answer (maybe because is not there).

No shelly it's proof. Don't try to downplay it. There have been no strong objections. In fact I am yet to see any thing put on the table that adds up.
Words don't cut it for me. Anybody can say anything.

You call for dust and rain patterns as proof, but they are too heavy so they are not; you call for opticla distortions due to density, but they can not be visible under the shadow of the floor; you post cfd picture, but this level of detail is beyond what can be realised with homemade cfd.

They are not too heavy. Only by your standard. That homemade CFD just silenced many know it all journalists. So much so they can't show their face in the thread again.
There is no such thing as homemade CFD.

So you can not rely on these things as evidence to prove your point; you should try something differnt, like smikle is doing. For exampleasking for evidence abot where does th outward momentum of the exhausts go, and expecting it to go outward if there s not some force to nullfy it and invert it. And so on.

Smikle isn't doing anything different. He's just giving you a chance to expose your reasoning. He well knows the solution.

Now i am asking you politely to provide evidence in the form of an image, and some reasoning.
I have never seen a 600 mph stream of gas take a 2m turning radius. As it involves external forces which does not exits around a formula 1 car.
I am asking that you show me this as i am willing to understand what you are putting forward.

[Richard]

What about the exhaust forming a vortex along the floor edge? That would explain the dust being kicked outward.

I can't see why Renault would go to the complication of an FEE unless it had some aero benefit (drag or downforce) that was greater than a blown diffuser.

A sideways jet doesn't seem to give any benefit, so that isn't the answer unless Renault completely lost the plot.

[Pierce89]

My first thought on seeing the video is that the car is turning, the exhaust is kicking up the dust, and we are looking at a trace of the car's path around that bend.

We can't discount that the car is turning. The exhaust kicks up some dust, the car travels forward and turns right, so the point at which the dust is kicked up is then offset to the side of the car.

There is also some merit in the water splash analogy. The initial impact of the exhaust would be outward. However, would the dust continue on that path if the exhaust formed a vortex down the edge of the car? Is it reasonable to expect the dust to form a nice vortex like smoke in a wind tunnel, or would the dust kick up and get flung out as the vortex hit the ground?

Finally, how long had the dust lain there? Had it previously been stored in a bucket, open to the damp sea air?

Richard here is a straight:

This a snap shot from the car moving straight for quite a while.

The Renault team have said the exhaust blow the floor. I know you all think that's to throw everyone off, but In the picture it looks like the exhaust and mist go back under the car to me.

[malcolm]

ringo, do you read others' post or do you just reread yours? Dust is blown outward, while gases are inward. I have written it several times and all the others here agree on that.

This is not possible IMO. I've asked you to sketch how it is possible and you have not responded. Ever used a leaf blower to blow dust?
It would be a useless tool if the dust went the opposite of the blowing direction.

Ringo, take some time to consider what Shelly actually means. You briefly read what is said, jump to a conclusion, and then begin arguing without taking a moment to consider that what was said may actually mean something else.

What was meant is that since the dust is propelled by the exhaust, there must be a velocity differential between the exhaust/air mixture and the dust in order for the dust to change direction. If there is a velocity differential, and the exhaust/air mixture follows a curve rather than a straight line, then it would be impossible for the two to follow the exact same trajectory. They may be close, or they may not be, but blurry snapshots of cement dust clouds does not make for concrete scientific evidence (pardon the pun) as to how similar the trajectories are.

Thought experiment: The exhaust is leaving the exhaust with a lateral component of velocity of 400 km/h, while the dust is stationary on the ground. The drag force of each dust particle speeds up the dust as the exhaust slows down after exiting the end of the exhaust pipe. As the exhaust mixes with the cross-flowing air, it will begin to accelerate rearward. As the dust begins to feel the longitudinal drag force from the cross-flow, it will also begin to accelerate rearward, although at a different rate. If the exhaust/air mixture then feels the effects of the diffuser, some of it will then begin to accelerate inward. Of course, the dust will then begin to feel that drag force, and will accelerate inward.

Note that I have said nothing of velocity of the dust, just acceleration.

Even though the dust is first accelerated outward, then rearward, then inward, it may still have a lateral component of velocity that it outward, due to the inertia of the dust particle.

Essentially, what I am saying is that it is the differential in velocity between the exhaust/air mixture and the dust that accelerates each dust particle due to its drag force. Therefore, the exhaust/air mixture would HAVE to turn a tighter radius than the dust, as the dust cannot accelerate without that differential in velocity.

That's not a proof that all exhaust goes under the diffuser, just merely a proof that the trajectory of the exhaust and the dust is NOT the EXACT same.