Learning Forum

[moritz.ursprung]

Hello,

is it possible to create pathlines only in a specified intervall?

For example I have a 2D geometry and start the pathlines from a line I defined. Now I want the pathlines to only run until a second line I define instead of to the end of the domain. doing so by defining the number of steps does not do the trick, because not all pathlines reach the second border after the same amount of steps.

.

[Rob]

Looking at the panel there's not a cell zone option, so it doesn't look like it's possible in Fluent. If there's an interior surface at that position have a look at massless DPM tracks if the interior is set to escape (you may need to use a porous jump for that option). 

[NickFL]

I hate to disagree with Rob here, but maybe there is a way. I would create a surface at the x-location you want to end the streamlines at using Surfaces->Isosurface of Constant X -> value. Also give this a good name. Then when creating your pathlines, use this newly created surface (actually it is a line because we are in 2D) and check the reverse box. This will seed the streamlines along the line, but move in the upstream direction until it reaches the inlet. 

[Rob]

Good idea - I was thinking on how to terminate pathlines at an arbitary point, reverse solves that by killing them at the inlet. The only drawback will be if you don't have a good release surface relative to the channels: ie you may find very few pathlines in certain channels. 

[moritz.ursprung]

 

Thanks for the hint @NickFL. I also saw the reverse option.

It works quite well for laminar flow, as is the first image I posted. Unfornutantely I also want to look at flows with lots of vortexes. 

As you can see in the image the pathlines do not only run in the direction of the inlet (which was not the starting point in the first post anyways). Also as Rob pointed out, the number of pathlines is limited.

I might still be able to use this to generate some data. I’ll just have to ignore those pathlines from vortexes downstream.

So if anyone still has an idea on how to create pathlines only between to lines/sufeaces which are not inlet or outlet, I would still be happy to hear it!

EDIT: I might get this to work with getting the data of the coordinate over the path length. Then I can calculate how long the path of every pathline between my set borders is, and retrieve all other values only within the path length of the specific pathline. I hope it's clear what I am trying to explain.

 

[NickFL]

Yes having the line in the wake of those front cylinders will cause a problem. You could select locations on the line only outside the recirculation bubble of the objects. What does your convergence look like? Also you mesh may be a bit to coarse for the scale you have there. Are you already at the limit of the student license?

One thing to keep in mind is that these upstream objects will shed vorticies and these will have certain frequency. The solver could actually trying to resolve this shedding (to determine if this is the case, look at how the residuals are behaving). One approach to elminate this would be to increase the "pseudo" timestep. Another approach would be to run it as a URANS, and then turn on the time averaging for the velocity. You could then do streamlines on that averaged velocity field. 

[Rob]

Is the bit to the right a separate cell zone? If the case & data are saved you could deactive it so it's no longer in the model. You'd want to reload the saved case & data to continue working though. 

[moritz.ursprung]

That's another good hint, thanks. Right now the hole domain is one cell zone, but I could split it, if the procedure as described above doesn't work