Exhaust Blown Floor - Forward Exhaust Exit

[malcolm]

Ok, I'll try another way.

Say there are golf balls under the car as it is driving over them at 200 mph. The exhaust would push them outward, and then the cross-flow (and the flow inward toward the diffuser, if the air does that) would then begin to push the golf ball inwards, either merely slowing it down or even in toward the diffuser; however, since it has more mass than the air, it would take a while for it get pushed inward by the air, and might just end up following an entirely different trajectory.

Now, applying the dust, it is still heavier than air, so it will not follow the same trajectory as airflow. It's that simple. It might be close to the same trajectory, depending how light the particles are, but it will not be the same.

Here's the important part:

For anything to get pushed by air, obviously the air is travelling at a different velocity (speed with a direction vector). It can't work any other way.

[Formula None]

Gasses cannot pull objects.

Que?

[shelly]

@n_smikle: why do you count air under the car and out of the car in two different categories? as there is no reason to do it, so I am not missing anything.
As for the push pull, I have already written that I do not understand what the point is: can you explain what you mean by pull, and why it is not possible?
Apart from this, I think we all agree that air comes into the diffuser from the sides also, so we can skip the push-pull point or treat it as a sidee isssue.

I'll try to explain my point so that it is more clear: exhausts accelerate dust to the outside, then both the exhaust and the dust are exposed to the airflow, which acts on them with different effects due to their different inertia.
Lighter exhausts will follow a tighter path.
Concrete dust is far too heavy to follow ambient air. You need particles half a micron in diameter to have a good tracking performance, that's a order of magnitude smaller than concrete dust.
Even then, hot exhausts are still three times lighter, so to trace them you would need even smaller particles.

@strad: you have to learn how to behave. After that, you have to learn how to discuss

[marekk]

And Cement dust, have anybody here ever opened a bag of cement? It is lighter than baby powder - you can reasonably expect it to give a good trace of the exhaust. It is not like the exhaust is in a solid walled tube - you have bodies of air around it that push on it - and guess what.... the push wasn't hard enough to curl the exhaust nor the cement dust under the car. So there is only one reasonable conclusion...

Did yesterday some repairs in the garden and can confirm - cement dust is really fine.
That said, it's still > 10 microns in diameter, compared to 0,0006 microns for carbon dioxide molecules. That's 16,000 times more.

There is big difference between pushing and pulling in fluids - just try to blow out the candle by sucking the air (be carefull ).

As mentioned in previous post - we have to wait for some oil smoke from broken engine (0,03 micron - still 100 times heavier then exhaust gases) to have a clue about real flows.

[PlatinumZealot]

Gasses cannot pull objects.

Que?

Let me educate you... are you ready or you want to read up on vaccum pumps then retract that?

I have done a lot of work with REAL vacuum pumps.

OK... I will educate you for the sake of embarrassment..
I will draw a simple free body diagram... Just for you.

This is always why I say, the FUNDAMENTALS are key.... some people misunderstand the fundamentals, I never thought you would, Formula none.

[ringo]

Ok, I'll try another way.

Say there are golf balls under the car as it is driving over them at 200 mph. The exhaust would push them outward, and then the cross-flow (and the flow inward toward the diffuser, if the air does that) would then begin to push the golf ball inwards, either merely slowing it down or even in toward the diffuser; however, since it has more mass than the air, it would take a while for it get pushed inward by the air, and might just end up following an entirely different trajectory.

Now, applying the dust, it is still heavier than air, so it will not follow the same trajectory as airflow. It's that simple. It might be close to the same trajectory, depending how light the particles are, but it will not be the same.

Here's the important part:

For anything to get pushed by air, obviously the air is travelling at a different velocity (speed with a direction vector). It can't work any other way.

This is grasping for straws.

It's time to take snap shots of the video now and post them in the thread.
Let's hear the explanations.

Cause i never heard of this dissonance between particles and a propellant.

I guess paint coming out a spray can is going in a completely different direction than the gas.
The gas kicks the paint out the can, like fred flintstone kicking out the saber tooth, and makes a full 180 turn and goes back inside. LoL
[youtube]http://www.youtube.com/watch?v=GJu8RreA ... re=related[/youtube]

[ringo]

And Cement dust, have anybody here ever opened a bag of cement? It is lighter than baby powder - you can reasonably expect it to give a good trace of the exhaust. It is not like the exhaust is in a solid walled tube - you have bodies of air around it that push on it - and guess what.... the push wasn't hard enough to curl the exhaust nor the cement dust under the car. So there is only one reasonable conclusion...

Did yesterday some repairs in the garden and can confirm - cement dust is really fine.
That said, it's still > 10 microns in diameter, compared to 0,0006 microns for carbon dioxide molecules. That's 16,000 times more.

There is big difference between pushing and pulling in fluids - just try to blow out the candle by sucking the air (be carefull ).

As mentioned in previous post - we have to wait for some oil smoke from broken engine (0,03 micron - still 100 times heavier then exhaust gases) to have a clue about real flows.

We don't have to wait for anything.

First it was common track dust, we got that in malaysia practice,
then it was rain, we got it again in china?,
then it was heat waves which are literally air molecules at their lowest density,
the we get a beautiful concrete dust trace.

It will never be good enough, because it doesn't agree with your opinion.

Forget about the oil spray, an engine failure is the worst example to use, and it wont happen this year with the renault engine.

The concrete dust is perfectly representing what is happening for us. It can't get better than that.

[Formula None]

Gasses cannot pull objects.

Que?

Let me educate you... are you ready or you want to read up on vaccum pumps then retract that?

I have done a lot of work with REAL vacuum pumps.

OK... I will educate you for the sake of embarrassment..
I will draw a simple free body diagram... Just for you.

This is always why I say, the FUNDAMENTALS are key.... some people misunderstand the fundamentals, I never thought you would, Formula none.

n_smikle, "que" is Spanish for "why." I ask why you said "gases can't pull objects" and for some reason you get very upset and say you're going to embarrass me somehow.

[PlatinumZealot]

Formula None.. I did this just for you.



Answer.. NONE..
Gasses can only produce positive pressure on the walls of their container. There is no such thing as a negative vacuum. In fact, even in the far reaches of space you will not encounter even zero vaccum.

The only way the piston will move to the left, is if another gas pushes it to the left or a solid pushes it left.. or a solid object such with a hook or some adhesive liquid.. any thing that produces a force to the left. A gas cannot produce a force to the left because the particles only produce a force normal to the walls of the container.

http://www.grc.nasa.gov/WWW/K-12/airplane/pressure.html

[Formula None]

I guess paint coming out a spray can is going in a completely different direction than the gas.
The gas kicks the paint out the can, like fred flintstone kicking out the saber tooth, and makes a full 180 turn and goes back inside. LoL

You know very well that's not the case they're making, why must you be argumentative? I think all they're saying is that dust and mist will not necessarily follow the same trajectory as airflow, due to inertia. Like how a vertical wall of spray is created by wheels in the rain, seemingly unaffected by airflow around the car. Please be an adult and not constantly offended when you are challenged by others. Just for the record, I'm not totally buying shelly & malcolms side of things either.

[PlatinumZealot]

n_smikle, "que" is Spanish for "why." I ask why you said "gases can't pull objects" and for some reason you get very upset and say you're going to embarrass me somehow.

OK..well I pounced because you posted a vacuum cleaner, and I thought you were implying that a vacuum cleaner proves that I was talking nonsense. Alrighty.. Well sorry for that.

[ringo]

Chillax man, i've got no reason for getting defensive. The FEE theory is not on the back foot, no reason to defend the fort.

That was clearly an illustrative joke. That comes to my mind when i imagine the dust getting kicked out from under the car and then the gas doubles back under and locks to the doors.

That video is just to show you that, you cannot have a propellant pushing something, in a similar medium, then suddenly the propelant decelerates, changes direction and still have the dust, or paint mysteriously flying on it's own.
And i am not talking about inertia here where the dust or paint still has some energy before it falls.
I mean lif the dust completely of the ground moving allong with the dust for about a meter then turning back under the floor. It's not possible.

Here is the pics like i promised:



that blue box gives some perspective. The wheel is 660mm tall. The width of the box to the edge of the floor is a meter or more. So the gas pushes the dust more than a meter wide. And knowing that the dust is heavier, who knows if the gas goes even wider.
Now how is the diffuser so strong that it can pull free air from a meter away?
Never saw that in my life.





explain these 2 above Mr. None.
I leave them to you.

edit: please draw where the gas turns back in, and tell me the turning radius of the gas, and tell me what phenomena is cause the exhuast to differentiate itself from ordinary free stream air. Why doesn't it mix and lose temperature after being so exposed?
If you have the time, draw a top view with the gas path. Same for Shelly, draw a top view with your idea of the gas path; knowing that we have these pictures as a guide.

[PlatinumZealot]

Ok, I'll try another way.

Say there are golf balls under the car as it is driving over them at 200 mph. The exhaust would push them outward, and then the cross-flow (and the flow inward toward the diffuser, if the air does that) would then begin to push the golf ball inwards, either merely slowing it down or even in toward the diffuser; however, since it has more mass than the air, it would take a while for it get pushed inward by the air, and might just end up following an entirely different trajectory.

Now, applying the dust, it is still heavier than air, so it will not follow the same trajectory as airflow. It's that simple. It might be close to the same trajectory, depending how light the particles are, but it will not be the same.

Here's the important part:

For anything to get pushed by air, obviously the air is travelling at a different velocity (speed with a direction vector). It can't work any other way.

Ok, I agree with the last pararagh. So this is question of the momentum of the cement dust after it intermixes with the exhaust particles then..

What is the minimum radius that the exhaust gas can move with the cement dust?

This is under the precedent that the Exhaust gases from the R31 exhaust is shot outwards (as seen in the video) then CURLS back under the floor - but you suspect, the cement dust is too heavy to curl under the floor with the gases. OK fair enough.

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.

2) The second part of the proof, is to find if at that temperature, turbulence and speed, how close can the intermingling cement dust be pushed along the radius of the exhaust stream as it goes under the floor.

Again, this is not my opinion, but I am being open minded and laying your suspicions out as if it were a problem.

[Formula None]

n_smikle, "que" is Spanish for "why." I ask why you said "gases can't pull objects" and for some reason you get very upset and say you're going to embarrass me somehow.

OK..well I pounced because you posted a vacuum cleaner, and I thought you were implying that a vacuum cleaner proves that I was talking nonsense. Alrighty.. Well sorry for that.

Well yeah I did think you were talking nonsense, it's why I asked. Or just confused about the point you were trying to make. In the context of this discussion it seems "push" or "pull" is subjective and only signifying direction of flow. So, "pulling" a dust particle under the floor (or, my little vacuum) and "pushing" the dust with the exhaust out from under the floor. Of course no one is implying that, beyond inertia, particles can magically move in a certain direction not roughly in the same trajectory as the gas. Is this what you think the counter-argument was?

[Formula None]

explain these 2 above Mr. None.
I leave them to you.

I'm not here to explain malcolm & shelly & other's ideas. Just because I don't take your ideas hook, line and sinker doesn't mean I totally buy theirs. I'm just reading this thread, trying to understand everyone's different hypothesis. You've done your cfd work, are very proud of it and lambast anyone who doubts it. When you misrepresent the counterarguments, I have to speak up. Doesn't mean I'm saying you're wrong, Ringo [...]

But if I had to guess, I'd say that the counterargument remains that the exhaust is accelerating the dust near its exit and propels it outward before being picked up by the freestream, while the exhaust itself cools, loses velocity and turns in toward the car. Not terribly convinced by this either, but I don't think they're terrible people for bringing it up.