malcolm wrote:
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.
Well he/she is not being clear. All i am asking for is an image. That is all.
I am reading and trying my best to understand, but an image would do just fine for me.
Is that too much to ask?
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.
Well the exhuast doesn't follow a deep curve, it's parabolic in nature. This wasproven scientifically by using equation from a research paper on mixed flows.
remember this marek?
based on a paper that was posted.
and average trajectory would be the same, as it is a mixutre. A spray paint can being used in an example. There is an average trajectory that is clearly defined in the image.
It's the same for flow vis. Will you say the engineers are using flow vis or string when it deosn't represent the flow direction?
I am not dwelling too much on this, as it sidetracks the discussion into something that isn't really an issue. dust is a good indicator of the flow direction.
You can't just make up rules and say what works and what doesn't work when there is no evidence to back it up. Can't just say concrete dust is not good enough.
Science doesn't work like that. I am going by observation and correlation. And the correlation is looking good.
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.
Yes.
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.
You loss me there. There is no support for that statement. Remember that dyson vacuum example. The air is curling and the dust is following.
Then you have these things:
[youtube]
http://www.youtube.com/watch?v=tj5uvC9cLO4[/youtube]
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.
Its from video. Thanks to strad you can download it and look for yourself.
The video is very clear. I can rewind and play all day. Much thanks to strad again.
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.
The dust isn't feeling the cross flow. Remember the air is still and the car is moving through it. The car pulls allong the air, which the is pushing the dust particles as it moves forward with the car, while the exhuasts would push the dust back.
The dust only acclerates rearward from the exhaust, not the flow around the car with is going in the opposite direction relative to the exhausts.
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.
There is no effect of the diffuser that exists outside of the floor area. The diffuser is not a pump. It is just an end "fitting" with a low restriction.
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.
I haven't seen it move inward. And you haven't either. So i can't follow what is contradicting the evidence. Though i'll listen to what you are saying.
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.
No there is a misunderstanding that you have. If i only had that scholarly article, i would post it for you to run through.
You cannot take the exhuast curving as fact, becuase it doesn't take a radius. It's a parabola that diverges from the center line of the car. It doesn't really come close to the car after it leaves the pipe. At best it will run along the car.
I would like it if you drew an image. it's hard to follow words, as anyone can say anything which sounds like it is correct. Please, I keep asking for these and no one is contributing.
T
hat'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.
It's not a proof. But i do know the trajectory is not exactly the same. What it is though is it's in the same general direction. One doesn't go the opposite direction.
So i implore you to create an image in MS paint and post it,as when you draw something, it's more difficult to force something to work, as you have more time to consider what you are doing.
