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-   -   Different between trajectory and cut polt. (http://www.cfd-online.com/Forums/floefd-floworks-flotherm/127367-different-between-trajectory-cut-polt.html)

JosephKim December 9, 2013 22:54

Different between trajectory and cut polt.
 
I confirmed my calculation result.
And I saw velocity contour in the cylinder first. That is just ok because of good velocity distribution.
And Second, I saw tracjectories just I did like velocity contour. But trajectories was not expressed well contribution that is not equal to velocity contour.

Who knows, why this status occur?

I think, I have a 2011 version of FloEFD. So this version has lack of expression about detail trajectories. Is that right?

What do you think of this? Please comment.
Thank you.
http://blog.naver.com/kwj21st

Boris_M December 10, 2013 10:07

Hi Joseph,

No, there is no lack in anyway with V11.
Trajectories are basically particles without any mass. You will define a certain amound of particles distributed over the reference surface you selected and they are then following the flow. They do not necessarily cover the full flow region because there are only some selected starting point for the particles.
That doesn't mean that in areas where there are no flow trajectories is no flow, there is just none of the particles you selected entering this area.
It is like with a candle, if you blow out the candle you can see smoke rising from the glowing wick. The smoke doesn't fill the whole room but that doesn't mean that in the areas the smoke is not exisiting that ther is no air of no flow. Just the smoke particles are not getting into that area.
Sometimes these areas are not in the core flow if you selected the inlet of the model or are in "dead water" so in some corner where there is barely any flow so particles usually don't get there.
Another example is a main traffic road where all the cars are driving (main flow) and then there is a small side road going off where no car is driving. That doesn't mean there cannot be any car or it is not allowed to drive, that road is just not interesting for the main traffic as it might lead to a dead end. So just like with the flow such a reagion is not the main path to go from inlet to outlet.

The velocity contours show the overall field of flow and the velocity of each area. If you use I think V12 you can also displac LIC or stream lines in the cut plot in addition to the contours and you will see that often in such areas there is some recirculation and only sometimes some particles which started at a certain position in the flow will pass through that or get even trapped in an never ending vortex etc.

Boris

JosephKim December 11, 2013 02:31

I see.. Thank you, Boris.
The main stream exist definitely.
http://blogfiles.naver.net/20131210_...gdh_JPEG/2.jpg
This is Velocity contour.
http://blogfiles.naver.net/20131210_...SWM_JPEG/1.jpg
And this is trajactories.

Inside of cylinder's velosity is 0.066m/s that shows good distribution. But the trajectory shows channeling.
(A-ha!, There is porous media in the Cylinder.)
Anyway as you mentioned, trajactories show channeling though, the space that has no streamline also has minor trajactories which are not expressed.

So the conclusions can be arranged.
-The Cylinder has good flow distribution. Also there are no channeling.
Right?:)
Or... this is not a straightforward problem, isn't it?

Boris_M December 16, 2013 11:17

Sorry, I cannot see any images.

Boris


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